text: # orm/mapper.py
  # Copyright (C) 2005-2017 the SQLAlchemy authors and contributors
  # <see AUTHORS file>
  #
  # This module is part of SQLAlchemy and is released under
  # the MIT License: http://www.opensource.org/licenses/mit-license.php
  
  """Logic to map Python classes to and from selectables.
  
  Defines the :class:`~sqlalchemy.orm.mapper.Mapper` class, the central
  configurational unit which associates a class with a database table.
  
  This is a semi-private module; the main configurational API of the ORM is
  available in :class:`~sqlalchemy.orm.`.
  
  """
  from __future__ import absolute_import
  
  import types
  import weakref
  from itertools import chain
  from collections import deque
  
  from .. import sql, util, log, exc as sa_exc, event, schema, inspection
  from ..sql import expression, visitors, operators, util as sql_util
  from . import instrumentation, attributes, exc as orm_exc, loading
  from . import properties
  from . import util as orm_util
  from .interfaces import MapperProperty, InspectionAttr, _MappedAttribute
  
  from .base import _class_to_mapper, _state_mapper, class_mapper, \
      state_str, _INSTRUMENTOR
  from .path_registry import PathRegistry
  
  import sys
  
  
  _mapper_registry = weakref.WeakKeyDictionary()
  _already_compiling = False
  
  _memoized_configured_property = util.group_expirable_memoized_property()
  
  
  # a constant returned by _get_attr_by_column to indicate
  # this mapper is not handling an attribute for a particular
  # column
  NO_ATTRIBUTE = util.symbol('NO_ATTRIBUTE')
  
  # lock used to synchronize the "mapper configure" step
  _CONFIGURE_MUTEX = util.threading.RLock()
  
  
  @inspection._self_inspects
  @log.class_logger
  class Mapper(InspectionAttr):
      """Define the correlation of class attributes to database table
      columns.
  
      The :class:`.Mapper` object is instantiated using the
      :func:`~sqlalchemy.orm.mapper` function.    For information
      about instantiating new :class:`.Mapper` objects, see
      that function's documentation.
  
  
      When :func:`.mapper` is used
      explicitly to link a user defined class with table
      metadata, this is referred to as *classical mapping*.
      Modern SQLAlchemy usage tends to favor the
      :mod:`sqlalchemy.ext.declarative` extension for class
      configuration, which
      makes usage of :func:`.mapper` behind the scenes.
  
      Given a particular class known to be mapped by the ORM,
      the :class:`.Mapper` which maintains it can be acquired
      using the :func:`.inspect` function::
  
          from sqlalchemy import inspect
  
          mapper = inspect(MyClass)
  
      A class which was mapped by the :mod:`sqlalchemy.ext.declarative`
      extension will also have its mapper available via the ``__mapper__``
      attribute.
  
  
      """
  
      _new_mappers = False
  
      def __init__(self,
                   class_,
                   local_table=None,
                   properties=None,
                   primary_key=None,
                   non_primary=False,
                   inherits=None,
                   inherit_condition=None,
                   inherit_foreign_keys=None,
                   extension=None,
                   order_by=False,
                   always_refresh=False,
                   version_id_col=None,
                   version_id_generator=None,
                   polymorphic_on=None,
                   _polymorphic_map=None,
                   polymorphic_identity=None,
                   concrete=False,
                   with_polymorphic=None,
                   allow_partial_pks=True,
                   batch=True,
                   column_prefix=None,
                   include_properties=None,
                   exclude_properties=None,
                   passive_updates=True,
                   passive_deletes=False,
                   confirm_deleted_rows=True,
                   eager_defaults=False,
                   legacy_is_orphan=False,
                   _compiled_cache_size=100,
                   ):
          r"""Return a new :class:`~.Mapper` object.
  
          This function is typically used behind the scenes
          via the Declarative extension.   When using Declarative,
          many of the usual :func:`.mapper` arguments are handled
          by the Declarative extension itself, including ``class_``,
          ``local_table``, ``properties``, and  ``inherits``.
          Other options are passed to :func:`.mapper` using
          the ``__mapper_args__`` class variable::
  
             class MyClass(Base):
                 __tablename__ = 'my_table'
                 id = Column(Integer, primary_key=True)
                 type = Column(String(50))
                 alt = Column("some_alt", Integer)
  
                 __mapper_args__ = {
                     'polymorphic_on' : type
                 }
  
  
          Explicit use of :func:`.mapper`
          is often referred to as *classical mapping*.  The above
          declarative example is equivalent in classical form to::
  
              my_table = Table("my_table", metadata,
                  Column('id', Integer, primary_key=True),
                  Column('type', String(50)),
                  Column("some_alt", Integer)
              )
  
              class MyClass(object):
                  pass
  
              mapper(MyClass, my_table,
                  polymorphic_on=my_table.c.type,
                  properties={
                      'alt':my_table.c.some_alt
                  })
  
          .. seealso::
  
              :ref:`classical_mapping` - discussion of direct usage of
              :func:`.mapper`
  
          :param class\_: The class to be mapped.  When using Declarative,
            this argument is automatically passed as the declared class
            itself.
  
          :param local_table: The :class:`.Table` or other selectable
             to which the class is mapped.  May be ``None`` if
             this mapper inherits from another mapper using single-table
             inheritance.   When using Declarative, this argument is
             automatically passed by the extension, based on what
             is configured via the ``__table__`` argument or via the
             :class:`.Table` produced as a result of the ``__tablename__``
             and :class:`.Column` arguments present.
  
          :param always_refresh: If True, all query operations for this mapped
             class will overwrite all data within object instances that already
             exist within the session, erasing any in-memory changes with
             whatever information was loaded from the database. Usage of this
             flag is highly discouraged; as an alternative, see the method
             :meth:`.Query.populate_existing`.
  
          :param allow_partial_pks: Defaults to True.  Indicates that a
             composite primary key with some NULL values should be considered as
             possibly existing within the database. This affects whether a
             mapper will assign an incoming row to an existing identity, as well
             as if :meth:`.Session.merge` will check the database first for a
             particular primary key value. A "partial primary key" can occur if
             one has mapped to an OUTER JOIN, for example.
  
          :param batch: Defaults to ``True``, indicating that save operations
             of multiple entities can be batched together for efficiency.
             Setting to False indicates
             that an instance will be fully saved before saving the next
             instance.  This is used in the extremely rare case that a
             :class:`.MapperEvents` listener requires being called
             in between individual row persistence operations.
  
          :param column_prefix: A string which will be prepended
             to the mapped attribute name when :class:`.Column`
             objects are automatically assigned as attributes to the
             mapped class.  Does not affect explicitly specified
             column-based properties.
  
             See the section :ref:`column_prefix` for an example.
  
          :param concrete: If True, indicates this mapper should use concrete
             table inheritance with its parent mapper.
  
             See the section :ref:`concrete_inheritance` for an example.
  
          :param confirm_deleted_rows: defaults to True; when a DELETE occurs
            of one more rows based on specific primary keys, a warning is
            emitted when the number of rows matched does not equal the number
            of rows expected.  This parameter may be set to False to handle the
            case where database ON DELETE CASCADE rules may be deleting some of
            those rows automatically.  The warning may be changed to an
            exception in a future release.
  
            .. versionadded:: 0.9.4 - added
               :paramref:`.mapper.confirm_deleted_rows` as well as conditional
               matched row checking on delete.
  
          :param eager_defaults: if True, the ORM will immediately fetch the
            value of server-generated default values after an INSERT or UPDATE,
            rather than leaving them as expired to be fetched on next access.
            This can be used for event schemes where the server-generated values
            are needed immediately before the flush completes.   By default,
            this scheme will emit an individual ``SELECT`` statement per row
            inserted or updated, which note can add significant performance
            overhead.  However, if the
            target database supports :term:`RETURNING`, the default values will
            be returned inline with the INSERT or UPDATE statement, which can
            greatly enhance performance for an application that needs frequent
            access to just-generated server defaults.
  
            .. versionchanged:: 0.9.0 The ``eager_defaults`` option can now
               make use of :term:`RETURNING` for backends which support it.
  
          :param exclude_properties: A list or set of string column names to
            be excluded from mapping.
  
            See :ref:`include_exclude_cols` for an example.
  
          :param extension: A :class:`.MapperExtension` instance or
             list of :class:`.MapperExtension` instances which will be applied
             to all operations by this :class:`.Mapper`.  **Deprecated.**
             Please see :class:`.MapperEvents`.
  
          :param include_properties: An inclusive list or set of string column
            names to map.
  
            See :ref:`include_exclude_cols` for an example.
  
          :param inherits: A mapped class or the corresponding :class:`.Mapper`
            of one indicating a superclass to which this :class:`.Mapper`
            should *inherit* from.   The mapped class here must be a subclass
            of the other mapper's class.   When using Declarative, this argument
            is passed automatically as a result of the natural class
            hierarchy of the declared classes.
  
            .. seealso::
  
              :ref:`inheritance_toplevel`
  
          :param inherit_condition: For joined table inheritance, a SQL
             expression which will
             define how the two tables are joined; defaults to a natural join
             between the two tables.
  
          :param inherit_foreign_keys: When ``inherit_condition`` is used and
             the columns present are missing a :class:`.ForeignKey`
             configuration, this parameter can be used to specify which columns
             are "foreign".  In most cases can be left as ``None``.
  
          :param legacy_is_orphan: Boolean, defaults to ``False``.
            When ``True``, specifies that "legacy" orphan consideration
            is to be applied to objects mapped by this mapper, which means
            that a pending (that is, not persistent) object is auto-expunged
            from an owning :class:`.Session` only when it is de-associated
            from *all* parents that specify a ``delete-orphan`` cascade towards
            this mapper.  The new default behavior is that the object is
            auto-expunged when it is de-associated with *any* of its parents
            that specify ``delete-orphan`` cascade.  This behavior is more
            consistent with that of a persistent object, and allows behavior to
            be consistent in more scenarios independently of whether or not an
            orphanable object has been flushed yet or not.
  
            See the change note and example at :ref:`legacy_is_orphan_addition`
            for more detail on this change.
  
            .. versionadded:: 0.8 - the consideration of a pending object as
              an "orphan" has been modified to more closely match the
              behavior as that of persistent objects, which is that the object
              is expunged from the :class:`.Session` as soon as it is
              de-associated from any of its orphan-enabled parents.  Previously,
              the pending object would be expunged only if de-associated
              from all of its orphan-enabled parents. The new flag
              ``legacy_is_orphan`` is added to :func:`.orm.mapper` which
              re-establishes the legacy behavior.
  
          :param non_primary: Specify that this :class:`.Mapper` is in addition
            to the "primary" mapper, that is, the one used for persistence.
            The :class:`.Mapper` created here may be used for ad-hoc
            mapping of the class to an alternate selectable, for loading
            only.
  
            :paramref:`.Mapper.non_primary` is not an often used option, but
            is useful in some specific :func:`.relationship` cases.
  
            .. seealso::
  
                :ref:`relationship_non_primary_mapper`
  
          :param order_by: A single :class:`.Column` or list of :class:`.Column`
             objects for which selection operations should use as the default
             ordering for entities.  By default mappers have no pre-defined
             ordering.
  
             .. deprecated:: 1.1 The :paramref:`.Mapper.order_by` parameter
                is deprecated.   Use :meth:`.Query.order_by` to determine the
                ordering of a result set.
  
          :param passive_deletes: Indicates DELETE behavior of foreign key
             columns when a joined-table inheritance entity is being deleted.
             Defaults to ``False`` for a base mapper; for an inheriting mapper,
             defaults to ``False`` unless the value is set to ``True``
             on the superclass mapper.
  
             When ``True``, it is assumed that ON DELETE CASCADE is configured
             on the foreign key relationships that link this mapper's table
             to its superclass table, so that when the unit of work attempts
             to delete the entity, it need only emit a DELETE statement for the
             superclass table, and not this table.
  
             When ``False``, a DELETE statement is emitted for this mapper's
             table individually.  If the primary key attributes local to this
             table are unloaded, then a SELECT must be emitted in order to
             validate these attributes; note that the primary key columns
             of a joined-table subclass are not part of the "primary key" of
             the object as a whole.
  
             Note that a value of ``True`` is **always** forced onto the
             subclass mappers; that is, it's not possible for a superclass
             to specify passive_deletes without this taking effect for
             all subclass mappers.
  
             .. versionadded:: 1.1
  
             .. seealso::
  
                 :ref:`passive_deletes` - description of similar feature as
                 used with :func:`.relationship`
  
                 :paramref:`.mapper.passive_updates` - supporting ON UPDATE
                 CASCADE for joined-table inheritance mappers
  
          :param passive_updates: Indicates UPDATE behavior of foreign key
             columns when a primary key column changes on a joined-table
             inheritance mapping.   Defaults to ``True``.
  
             When True, it is assumed that ON UPDATE CASCADE is configured on
             the foreign key in the database, and that the database will handle
             propagation of an UPDATE from a source column to dependent columns
             on joined-table rows.
  
             When False, it is assumed that the database does not enforce
             referential integrity and will not be issuing its own CASCADE
             operation for an update.  The unit of work process will
             emit an UPDATE statement for the dependent columns during a
             primary key change.
  
             .. seealso::
  
                 :ref:`passive_updates` - description of a similar feature as
                 used with :func:`.relationship`
  
                 :paramref:`.mapper.passive_deletes` - supporting ON DELETE
                 CASCADE for joined-table inheritance mappers
  
          :param polymorphic_on: Specifies the column, attribute, or
            SQL expression used to determine the target class for an
            incoming row, when inheriting classes are present.
  
            This value is commonly a :class:`.Column` object that's
            present in the mapped :class:`.Table`::
  
              class Employee(Base):
                  __tablename__ = 'employee'
  
                  id = Column(Integer, primary_key=True)
                  discriminator = Column(String(50))
  
                  __mapper_args__ = {
                      "polymorphic_on":discriminator,
                      "polymorphic_identity":"employee"
                  }
  
            It may also be specified
            as a SQL expression, as in this example where we
            use the :func:`.case` construct to provide a conditional
            approach::
  
              class Employee(Base):
                  __tablename__ = 'employee'
  
                  id = Column(Integer, primary_key=True)
                  discriminator = Column(String(50))
  
                  __mapper_args__ = {
                      "polymorphic_on":case([
                          (discriminator == "EN", "engineer"),
                          (discriminator == "MA", "manager"),
                      ], else_="employee"),
                      "polymorphic_identity":"employee"
                  }
  
            It may also refer to any attribute
            configured with :func:`.column_property`, or to the
            string name of one::
  
                  class Employee(Base):
                      __tablename__ = 'employee'
  
                      id = Column(Integer, primary_key=True)
                      discriminator = Column(String(50))
                      employee_type = column_property(
                          case([
                              (discriminator == "EN", "engineer"),
                              (discriminator == "MA", "manager"),
                          ], else_="employee")
                      )
  
                      __mapper_args__ = {
                          "polymorphic_on":employee_type,
                          "polymorphic_identity":"employee"
                      }
  
            .. versionchanged:: 0.7.4
                ``polymorphic_on`` may be specified as a SQL expression,
                or refer to any attribute configured with
                :func:`.column_property`, or to the string name of one.
  
            When setting ``polymorphic_on`` to reference an
            attribute or expression that's not present in the
            locally mapped :class:`.Table`, yet the value
            of the discriminator should be persisted to the database,
            the value of the
            discriminator is not automatically set on new
            instances; this must be handled by the user,
            either through manual means or via event listeners.
            A typical approach to establishing such a listener
            looks like::
  
                  from sqlalchemy import event
                  from sqlalchemy.orm import object_mapper
  
                  @event.listens_for(Employee, "init", propagate=True)
                  def set_identity(instance, *arg, **kw):
                      mapper = object_mapper(instance)
                      instance.discriminator = mapper.polymorphic_identity
  
            Where above, we assign the value of ``polymorphic_identity``
            for the mapped class to the ``discriminator`` attribute,
            thus persisting the value to the ``discriminator`` column
            in the database.
  
            .. warning::
  
               Currently, **only one discriminator column may be set**, typically
               on the base-most class in the hierarchy. "Cascading" polymorphic
               columns are not yet supported.
  
            .. seealso::
  
              :ref:`inheritance_toplevel`
  
          :param polymorphic_identity: Specifies the value which
            identifies this particular class as returned by the
            column expression referred to by the ``polymorphic_on``
            setting.  As rows are received, the value corresponding
            to the ``polymorphic_on`` column expression is compared
            to this value, indicating which subclass should
            be used for the newly reconstructed object.
  
          :param properties: A dictionary mapping the string names of object
             attributes to :class:`.MapperProperty` instances, which define the
             persistence behavior of that attribute.  Note that :class:`.Column`
             objects present in
             the mapped :class:`.Table` are automatically placed into
             ``ColumnProperty`` instances upon mapping, unless overridden.
             When using Declarative, this argument is passed automatically,
             based on all those :class:`.MapperProperty` instances declared
             in the declared class body.
  
          :param primary_key: A list of :class:`.Column` objects which define
             the primary key to be used against this mapper's selectable unit.
             This is normally simply the primary key of the ``local_table``, but
             can be overridden here.
  
          :param version_id_col: A :class:`.Column`
             that will be used to keep a running version id of rows
             in the table.  This is used to detect concurrent updates or
             the presence of stale data in a flush.  The methodology is to
             detect if an UPDATE statement does not match the last known
             version id, a
             :class:`~sqlalchemy.orm.exc.StaleDataError` exception is
             thrown.
             By default, the column must be of :class:`.Integer` type,
             unless ``version_id_generator`` specifies an alternative version
             generator.
  
             .. seealso::
  
                :ref:`mapper_version_counter` - discussion of version counting
                and rationale.
  
          :param version_id_generator: Define how new version ids should
            be generated.  Defaults to ``None``, which indicates that
            a simple integer counting scheme be employed.  To provide a custom
            versioning scheme, provide a callable function of the form::
  
                def generate_version(version):
                    return next_version
  
            Alternatively, server-side versioning functions such as triggers,
            or programmatic versioning schemes outside of the version id
            generator may be used, by specifying the value ``False``.
            Please see :ref:`server_side_version_counter` for a discussion
            of important points when using this option.
  
            .. versionadded:: 0.9.0 ``version_id_generator`` supports
               server-side version number generation.
  
            .. seealso::
  
               :ref:`custom_version_counter`
  
               :ref:`server_side_version_counter`
  
  
          :param with_polymorphic: A tuple in the form ``(<classes>,
              <selectable>)`` indicating the default style of "polymorphic"
              loading, that is, which tables are queried at once. <classes> is
              any single or list of mappers and/or classes indicating the
              inherited classes that should be loaded at once. The special value
              ``'*'`` may be used to indicate all descending classes should be
              loaded immediately. The second tuple argument <selectable>
              indicates a selectable that will be used to query for multiple
              classes.
  
              .. seealso::
  
                :ref:`with_polymorphic` - discussion of polymorphic querying
                techniques.
  
          """
  
          self.class_ = util.assert_arg_type(class_, type, 'class_')
  
          self.class_manager = None
  
          self._primary_key_argument = util.to_list(primary_key)
          self.non_primary = non_primary
  
          if order_by is not False:
              self.order_by = util.to_list(order_by)
              util.warn_deprecated(
                  "Mapper.order_by is deprecated."
                  "Use Query.order_by() in order to affect the ordering of ORM "
                  "result sets.")
  
          else:
              self.order_by = order_by
  
          self.always_refresh = always_refresh
  
          if isinstance(version_id_col, MapperProperty):
              self.version_id_prop = version_id_col
              self.version_id_col = None
          else:
              self.version_id_col = version_id_col
          if version_id_generator is False:
              self.version_id_generator = False
          elif version_id_generator is None:
              self.version_id_generator = lambda x: (x or 0) + 1
          else:
              self.version_id_generator = version_id_generator
  
          self.concrete = concrete
          self.single = False
          self.inherits = inherits
          self.local_table = local_table
          self.inherit_condition = inherit_condition
          self.inherit_foreign_keys = inherit_foreign_keys
          self._init_properties = properties or {}
          self._delete_orphans = []
          self.batch = batch
          self.eager_defaults = eager_defaults
          self.column_prefix = column_prefix
          self.polymorphic_on = expression._clause_element_as_expr(
              polymorphic_on)
          self._dependency_processors = []
          self.validators = util.immutabledict()
          self.passive_updates = passive_updates
          self.passive_deletes = passive_deletes
          self.legacy_is_orphan = legacy_is_orphan
          self._clause_adapter = None
          self._requires_row_aliasing = False
          self._inherits_equated_pairs = None
          self._memoized_values = {}
          self._compiled_cache_size = _compiled_cache_size
          self._reconstructor = None
          self._deprecated_extensions = util.to_list(extension or [])
          self.allow_partial_pks = allow_partial_pks
  
          if self.inherits and not self.concrete:
              self.confirm_deleted_rows = False
          else:
              self.confirm_deleted_rows = confirm_deleted_rows
  
          self._set_with_polymorphic(with_polymorphic)
  
          if isinstance(self.local_table, expression.SelectBase):
              raise sa_exc.InvalidRequestError(
                  "When mapping against a select() construct, map against "
                  "an alias() of the construct instead."
                  "This because several databases don't allow a "
                  "SELECT from a subquery that does not have an alias."
              )
  
          if self.with_polymorphic and \
              isinstance(self.with_polymorphic[1],
                         expression.SelectBase):
              self.with_polymorphic = (self.with_polymorphic[0],
                                       self.with_polymorphic[1].alias())
  
          # our 'polymorphic identity', a string name that when located in a
          #  result set row indicates this Mapper should be used to construct
          # the object instance for that row.
          self.polymorphic_identity = polymorphic_identity
  
          # a dictionary of 'polymorphic identity' names, associating those
          # names with Mappers that will be used to construct object instances
          # upon a select operation.
          if _polymorphic_map is None:
              self.polymorphic_map = {}
          else:
              self.polymorphic_map = _polymorphic_map
  
          if include_properties is not None:
              self.include_properties = util.to_set(include_properties)
          else:
              self.include_properties = None
          if exclude_properties:
              self.exclude_properties = util.to_set(exclude_properties)
          else:
              self.exclude_properties = None
  
          self.configured = False
  
          # prevent this mapper from being constructed
          # while a configure_mappers() is occurring (and defer a
          # configure_mappers() until construction succeeds)
          _CONFIGURE_MUTEX.acquire()
          try:
              self.dispatch._events._new_mapper_instance(class_, self)
              self._configure_inheritance()
              self._configure_legacy_instrument_class()
              self._configure_class_instrumentation()
              self._configure_listeners()
              self._configure_properties()
              self._configure_polymorphic_setter()
              self._configure_pks()
              Mapper._new_mappers = True
              self._log("constructed")
              self._expire_memoizations()
          finally:
              _CONFIGURE_MUTEX.release()
  
      # major attributes initialized at the classlevel so that
      # they can be Sphinx-documented.
  
      is_mapper = True
      """Part of the inspection API."""
  
      @property
      def mapper(self):
          """Part of the inspection API.
  
          Returns self.
  
          """
          return self
  
      @property
      def entity(self):
          r"""Part of the inspection API.
  
          Returns self.class\_.
  
          """
          return self.class_
  
      local_table = None
      """The :class:`.Selectable` which this :class:`.Mapper` manages.
  
      Typically is an instance of :class:`.Table` or :class:`.Alias`.
      May also be ``None``.
  
      The "local" table is the
      selectable that the :class:`.Mapper` is directly responsible for
      managing from an attribute access and flush perspective.   For
      non-inheriting mappers, the local table is the same as the
      "mapped" table.   For joined-table inheritance mappers, local_table
      will be the particular sub-table of the overall "join" which
      this :class:`.Mapper` represents.  If this mapper is a
      single-table inheriting mapper, local_table will be ``None``.
  
      .. seealso::
  
          :attr:`~.Mapper.mapped_table`.
  
      """
  
      mapped_table = None
      """The :class:`.Selectable` to which this :class:`.Mapper` is mapped.
  
      Typically an instance of :class:`.Table`, :class:`.Join`, or
      :class:`.Alias`.
  
      The "mapped" table is the selectable that
      the mapper selects from during queries.   For non-inheriting
      mappers, the mapped table is the same as the "local" table.
      For joined-table inheritance mappers, mapped_table references the
      full :class:`.Join` representing full rows for this particular
      subclass.  For single-table inheritance mappers, mapped_table
      references the base table.
  
      .. seealso::
  
          :attr:`~.Mapper.local_table`.
  
      """
  
      inherits = None
      """References the :class:`.Mapper` which this :class:`.Mapper`
      inherits from, if any.
  
      This is a *read only* attribute determined during mapper construction.
      Behavior is undefined if directly modified.
  
      """
  
      configured = None
      """Represent ``True`` if this :class:`.Mapper` has been configured.
  
      This is a *read only* attribute determined during mapper construction.
      Behavior is undefined if directly modified.
  
      .. seealso::
  
          :func:`.configure_mappers`.
  
      """
  
      concrete = None
      """Represent ``True`` if this :class:`.Mapper` is a concrete
      inheritance mapper.
  
      This is a *read only* attribute determined during mapper construction.
      Behavior is undefined if directly modified.
  
      """
  
      tables = None
      """An iterable containing the collection of :class:`.Table` objects
      which this :class:`.Mapper` is aware of.
  
      If the mapper is mapped to a :class:`.Join`, or an :class:`.Alias`
      representing a :class:`.Select`, the individual :class:`.Table`
      objects that comprise the full construct will be represented here.
  
      This is a *read only* attribute determined during mapper construction.
      Behavior is undefined if directly modified.
  
      """
  
      primary_key = None
      """An iterable containing the collection of :class:`.Column` objects
      which comprise the 'primary key' of the mapped table, from the
      perspective of this :class:`.Mapper`.
  
      This list is against the selectable in :attr:`~.Mapper.mapped_table`. In
      the case of inheriting mappers, some columns may be managed by a
      superclass mapper.  For example, in the case of a :class:`.Join`, the
      primary key is determined by all of the primary key columns across all
      tables referenced by the :class:`.Join`.
  
      The list is also not necessarily the same as the primary key column
      collection associated with the underlying tables; the :class:`.Mapper`
      features a ``primary_key`` argument that can override what the
      :class:`.Mapper` considers as primary key columns.
  
      This is a *read only* attribute determined during mapper construction.
      Behavior is undefined if directly modified.
  
      """
  
      class_ = None
      """The Python class which this :class:`.Mapper` maps.
  
      This is a *read only* attribute determined during mapper construction.
      Behavior is undefined if directly modified.
  
      """
  
      class_manager = None
      """The :class:`.ClassManager` which maintains event listeners
      and class-bound descriptors for this :class:`.Mapper`.
  
      This is a *read only* attribute determined during mapper construction.
      Behavior is undefined if directly modified.
  
      """
  
      single = None
      """Represent ``True`` if this :class:`.Mapper` is a single table
      inheritance mapper.
  
      :attr:`~.Mapper.local_table` will be ``None`` if this flag is set.
  
      This is a *read only* attribute determined during mapper construction.
      Behavior is undefined if directly modified.
  
      """
  
      non_primary = None
      """Represent ``True`` if this :class:`.Mapper` is a "non-primary"
      mapper, e.g. a mapper that is used only to selet rows but not for
      persistence management.
  
      This is a *read only* attribute determined during mapper construction.
      Behavior is undefined if directly modified.
  
      """
  
      polymorphic_on = None
      """The :class:`.Column` or SQL expression specified as the
      ``polymorphic_on`` argument
      for this :class:`.Mapper`, within an inheritance scenario.
  
      This attribute is normally a :class:`.Column` instance but
      may also be an expression, such as one derived from
      :func:`.cast`.
  
      This is a *read only* attribute determined during mapper construction.
      Behavior is undefined if directly modified.
  
      """
  
      polymorphic_map = None
      """A mapping of "polymorphic identity" identifiers mapped to
      :class:`.Mapper` instances, within an inheritance scenario.
  
      The identifiers can be of any type which is comparable to the
      type of column represented by :attr:`~.Mapper.polymorphic_on`.
  
      An inheritance chain of mappers will all reference the same
      polymorphic map object.  The object is used to correlate incoming
      result rows to target mappers.
  
      This is a *read only* attribute determined during mapper construction.
      Behavior is undefined if directly modified.
  
      """
  
      polymorphic_identity = None
      """Represent an identifier which is matched against the
      :attr:`~.Mapper.polymorphic_on` column during result row loading.
  
      Used only with inheritance, this object can be of any type which is
      comparable to the type of column represented by
      :attr:`~.Mapper.polymorphic_on`.
  
      This is a *read only* attribute determined during mapper construction.
      Behavior is undefined if directly modified.
  
      """
  
      base_mapper = None
      """The base-most :class:`.Mapper` in an inheritance chain.
  
      In a non-inheriting scenario, this attribute will always be this
      :class:`.Mapper`.   In an inheritance scenario, it references
      the :class:`.Mapper` which is parent to all other :class:`.Mapper`
      objects in the inheritance chain.
  
      This is a *read only* attribute determined during mapper construction.
      Behavior is undefined if directly modified.
  
      """
  
      columns = None
      """A collection of :class:`.Column` or other scalar expression
      objects maintained by this :class:`.Mapper`.
  
      The collection behaves the same as that of the ``c`` attribute on
      any :class:`.Table` object, except that only those columns included in
      this mapping are present, and are keyed based on the attribute name
      defined in the mapping, not necessarily the ``key`` attribute of the
      :class:`.Column` itself.   Additionally, scalar expressions mapped
      by :func:`.column_property` are also present here.
  
      This is a *read only* attribute determined during mapper construction.
      Behavior is undefined if directly modified.
  
      """
  
      validators = None
      """An immutable dictionary of attributes which have been decorated
      using the :func:`~.orm.validates` decorator.
  
      The dictionary contains string attribute names as keys
      mapped to the actual validation method.
  
      """
  
      c = None
      """A synonym for :attr:`~.Mapper.columns`."""
  
      @util.memoized_property
      def _path_registry(self):
          return PathRegistry.per_mapper(self)
  
      def _configure_inheritance(self):
          """Configure settings related to inherting and/or inherited mappers
          being present."""
  
          # a set of all mappers which inherit from this one.
          self._inheriting_mappers = util.WeakSequence()
  
          if self.inherits:
              if isinstance(self.inherits, type):
                  self.inherits = class_mapper(self.inherits, configure=False)
              if not issubclass(self.class_, self.inherits.class_):
                  raise sa_exc.ArgumentError(
                      "Class '%s' does not inherit from '%s'" %
                      (self.class_.__name__, self.inherits.class_.__name__))
              if self.non_primary != self.inherits.non_primary:
                  np = not self.non_primary and "primary" or "non-primary"
                  raise sa_exc.ArgumentError(
                      "Inheritance of %s mapper for class '%s' is "
                      "only allowed from a %s mapper" %
                      (np, self.class_.__name__, np))
              # inherit_condition is optional.
              if self.local_table is None:
                  self.local_table = self.inherits.local_table
                  self.mapped_table = self.inherits.mapped_table
                  self.single = True
              elif self.local_table is not self.inherits.local_table:
                  if self.concrete:
                      self.mapped_table = self.local_table
                      for mapper in self.iterate_to_root():
                          if mapper.polymorphic_on is not None:
                              mapper._requires_row_aliasing = True
                  else:
                      if self.inherit_condition is None:
                          # figure out inherit condition from our table to the
                          # immediate table of the inherited mapper, not its
                          # full table which could pull in other stuff we don't
                          # want (allows test/inheritance.InheritTest4 to pass)
                          self.inherit_condition = sql_util.join_condition(
                              self.inherits.local_table,
                              self.local_table)
                      self.mapped_table = sql.join(
                          self.inherits.mapped_table,
                          self.local_table,
                          self.inherit_condition)
  
                      fks = util.to_set(self.inherit_foreign_keys)
                      self._inherits_equated_pairs = \
                          sql_util.criterion_as_pairs(
                              self.mapped_table.onclause,
                              consider_as_foreign_keys=fks)
              else:
                  self.mapped_table = self.local_table
  
              if self.polymorphic_identity is not None and not self.concrete:
                  self._identity_class = self.inherits._identity_class
              else:
                  self._identity_class = self.class_
  
              if self.version_id_col is None:
                  self.version_id_col = self.inherits.version_id_col
                  self.version_id_generator = self.inherits.version_id_generator
              elif self.inherits.version_id_col is not None and \
                      self.version_id_col is not self.inherits.version_id_col:
                  util.warn(
                      "Inheriting version_id_col '%s' does not match inherited "
                      "version_id_col '%s' and will not automatically populate "
                      "the inherited versioning column. "
                      "version_id_col should only be specified on "
                      "the base-most mapper that includes versioning." %
                      (self.version_id_col.description,
                       self.inherits.version_id_col.description)
                  )
  
              if self.order_by is False and \
                      not self.concrete and \
                      self.inherits.order_by is not False:
                  self.order_by = self.inherits.order_by
  
              self.polymorphic_map = self.inherits.polymorphic_map
              self.batch = self.inherits.batch
              self.inherits._inheriting_mappers.append(self)
              self.base_mapper = self.inherits.base_mapper
              self.passive_updates = self.inherits.passive_updates
              self.passive_deletes = self.inherits.passive_deletes or \
                  self.passive_deletes
              self._all_tables = self.inherits._all_tables
  
              if self.polymorphic_identity is not None:
                  if self.polymorphic_identity in self.polymorphic_map:
                      util.warn(
                          "Reassigning polymorphic association for identity %r "
                          "from %r to %r: Check for duplicate use of %r as "
                          "value for polymorphic_identity." %
                          (self.polymorphic_identity,
                           self.polymorphic_map[self.polymorphic_identity],
                           self, self.polymorphic_identity)
                      )
                  self.polymorphic_map[self.polymorphic_identity] = self
  
          else:
              self._all_tables = set()
              self.base_mapper = self
              self.mapped_table = self.local_table
              if self.polymorphic_identity is not None:
                  self.polymorphic_map[self.polymorphic_identity] = self
              self._identity_class = self.class_
  
          if self.mapped_table is None:
              raise sa_exc.ArgumentError(
                  "Mapper '%s' does not have a mapped_table specified."
                  % self)
  
      def _set_with_polymorphic(self, with_polymorphic):
          if with_polymorphic == '*':
              self.with_polymorphic = ('*', None)
          elif isinstance(with_polymorphic, (tuple, list)):
              if isinstance(
                      with_polymorphic[0], util.string_types + (tuple, list)):
                  self.with_polymorphic = with_polymorphic
              else:
                  self.with_polymorphic = (with_polymorphic, None)
          elif with_polymorphic is not None:
              raise sa_exc.ArgumentError("Invalid setting for with_polymorphic")
          else:
              self.with_polymorphic = None
  
          if isinstance(self.local_table, expression.SelectBase):
              raise sa_exc.InvalidRequestError(
                  "When mapping against a select() construct, map against "
                  "an alias() of the construct instead."
                  "This because several databases don't allow a "
                  "SELECT from a subquery that does not have an alias."
              )
  
          if self.with_polymorphic and \
              isinstance(self.with_polymorphic[1],
                         expression.SelectBase):
              self.with_polymorphic = (self.with_polymorphic[0],
                                       self.with_polymorphic[1].alias())
          if self.configured:
              self._expire_memoizations()
  
      def _set_concrete_base(self, mapper):
          """Set the given :class:`.Mapper` as the 'inherits' for this
          :class:`.Mapper`, assuming this :class:`.Mapper` is concrete
          and does not already have an inherits."""
  
          assert self.concrete
          assert not self.inherits
          assert isinstance(mapper, Mapper)
          self.inherits = mapper
          self.inherits.polymorphic_map.update(self.polymorphic_map)
          self.polymorphic_map = self.inherits.polymorphic_map
          for mapper in self.iterate_to_root():
              if mapper.polymorphic_on is not None:
                  mapper._requires_row_aliasing = True
          self.batch = self.inherits.batch
          for mp in self.self_and_descendants:
              mp.base_mapper = self.inherits.base_mapper
          self.inherits._inheriting_mappers.append(self)
          self.passive_updates = self.inherits.passive_updates
          self._all_tables = self.inherits._all_tables
          for key, prop in mapper._props.items():
              if key not in self._props and \
                  not self._should_exclude(key, key, local=False,
                                           column=None):
                  self._adapt_inherited_property(key, prop, False)
  
      def _set_polymorphic_on(self, polymorphic_on):
          self.polymorphic_on = polymorphic_on
          self._configure_polymorphic_setter(True)
  
      def _configure_legacy_instrument_class(self):
  
          if self.inherits:
              self.dispatch._update(self.inherits.dispatch)
              super_extensions = set(
                  chain(*[m._deprecated_extensions
                          for m in self.inherits.iterate_to_root()]))
          else:
              super_extensions = set()
  
          for ext in self._deprecated_extensions:
              if ext not in super_extensions:
                  ext._adapt_instrument_class(self, ext)
  
      def _configure_listeners(self):
          if self.inherits:
              super_extensions = set(
                  chain(*[m._deprecated_extensions
                          for m in self.inherits.iterate_to_root()]))
          else:
              super_extensions = set()
  
          for ext in self._deprecated_extensions:
              if ext not in super_extensions:
                  ext._adapt_listener(self, ext)
  
      def _configure_class_instrumentation(self):
          """If this mapper is to be a primary mapper (i.e. the
          non_primary flag is not set), associate this Mapper with the
          given class_ and entity name.
  
          Subsequent calls to ``class_mapper()`` for the class_/entity
          name combination will return this mapper.  Also decorate the
          `__init__` method on the mapped class to include optional
          auto-session attachment logic.
  
          """
  
          manager = attributes.manager_of_class(self.class_)
  
          if self.non_primary:
              if not manager or not manager.is_mapped:
                  raise sa_exc.InvalidRequestError(
                      "Class %s has no primary mapper configured.  Configure "
                      "a primary mapper first before setting up a non primary "
                      "Mapper." % self.class_)
              self.class_manager = manager
              self._identity_class = manager.mapper._identity_class
              _mapper_registry[self] = True
              return
  
          if manager is not None:
              assert manager.class_ is self.class_
              if manager.is_mapped:
                  raise sa_exc.ArgumentError(
                      "Class '%s' already has a primary mapper defined. "
                      "Use non_primary=True to "
                      "create a non primary Mapper.  clear_mappers() will "
                      "remove *all* current mappers from all classes." %
                      self.class_)
              # else:
                  # a ClassManager may already exist as
                  # ClassManager.instrument_attribute() creates
                  # new managers for each subclass if they don't yet exist.
  
          _mapper_registry[self] = True
  
          # note: this *must be called before instrumentation.register_class*
          # to maintain the documented behavior of instrument_class
          self.dispatch.instrument_class(self, self.class_)
  
          if manager is None:
              manager = instrumentation.register_class(self.class_)
  
          self.class_manager = manager
  
          manager.mapper = self
          manager.deferred_scalar_loader = util.partial(
              loading.load_scalar_attributes, self)
  
          # The remaining members can be added by any mapper,
          # e_name None or not.
          if manager.info.get(_INSTRUMENTOR, False):
              return
  
          event.listen(manager, 'first_init', _event_on_first_init, raw=True)
          event.listen(manager, 'init', _event_on_init, raw=True)
  
          for key, method in util.iterate_attributes(self.class_):
              if isinstance(method, types.FunctionType):
                  if hasattr(method, '__sa_reconstructor__'):
                      self._reconstructor = method
                      event.listen(manager, 'load', _event_on_load, raw=True)
                  elif hasattr(method, '__sa_validators__'):
                      validation_opts = method.__sa_validation_opts__
                      for name in method.__sa_validators__:
                          if name in self.validators:
                              raise sa_exc.InvalidRequestError(
                                  "A validation function for mapped "
                                  "attribute %r on mapper %s already exists." %
                                  (name, self))
                          self.validators = self.validators.union(
                              {name: (method, validation_opts)}
                          )
  
          manager.info[_INSTRUMENTOR] = self
  
      @classmethod
      def _configure_all(cls):
          """Class-level path to the :func:`.configure_mappers` call.
          """
          configure_mappers()
  
      def dispose(self):
          # Disable any attribute-based compilation.
          self.configured = True
  
          if hasattr(self, '_configure_failed'):
              del self._configure_failed
  
          if not self.non_primary and \
              self.class_manager is not None and \
              self.class_manager.is_mapped and \
                  self.class_manager.mapper is self:
              instrumentation.unregister_class(self.class_)
  
      def _configure_pks(self):
          self.tables = sql_util.find_tables(self.mapped_table)
  
          self._pks_by_table = {}
          self._cols_by_table = {}
  
          all_cols = util.column_set(chain(*[
              col.proxy_set for col in
              self._columntoproperty]))
  
          pk_cols = util.column_set(c for c in all_cols if c.primary_key)
  
          # identify primary key columns which are also mapped by this mapper.
          tables = set(self.tables + [self.mapped_table])
          self._all_tables.update(tables)
          for t in tables:
              if t.primary_key and pk_cols.issuperset(t.primary_key):
                  # ordering is important since it determines the ordering of
                  # mapper.primary_key (and therefore query.get())
                  self._pks_by_table[t] = \
                      util.ordered_column_set(t.primary_key).\
                      intersection(pk_cols)
              self._cols_by_table[t] = \
                  util.ordered_column_set(t.c).\
                  intersection(all_cols)
  
          # if explicit PK argument sent, add those columns to the
          # primary key mappings
          if self._primary_key_argument:
              for k in self._primary_key_argument:
                  if k.table not in self._pks_by_table:
                      self._pks_by_table[k.table] = util.OrderedSet()
                  self._pks_by_table[k.table].add(k)
  
          # otherwise, see that we got a full PK for the mapped table
          elif self.mapped_table not in self._pks_by_table or \
                  len(self._pks_by_table[self.mapped_table]) == 0:
              raise sa_exc.ArgumentError(
                  "Mapper %s could not assemble any primary "
                  "key columns for mapped table '%s'" %
                  (self, self.mapped_table.description))
          elif self.local_table not in self._pks_by_table and \
                  isinstance(self.local_table, schema.Table):
              util.warn("Could not assemble any primary "
                        "keys for locally mapped table '%s' - "
                        "no rows will be persisted in this Table."
                        % self.local_table.description)
  
          if self.inherits and \
                  not self.concrete and \
                  not self._primary_key_argument:
              # if inheriting, the "primary key" for this mapper is
              # that of the inheriting (unless concrete or explicit)
              self.primary_key = self.inherits.primary_key
          else:
              # determine primary key from argument or mapped_table pks -
              # reduce to the minimal set of columns
              if self._primary_key_argument:
                  primary_key = sql_util.reduce_columns(
                      [self.mapped_table.corresponding_column(c) for c in
                       self._primary_key_argument],
                      ignore_nonexistent_tables=True)
              else:
                  primary_key = sql_util.reduce_columns(
                      self._pks_by_table[self.mapped_table],
                      ignore_nonexistent_tables=True)
  
              if len(primary_key) == 0:
                  raise sa_exc.ArgumentError(
                      "Mapper %s could not assemble any primary "
                      "key columns for mapped table '%s'" %
                      (self, self.mapped_table.description))
  
              self.primary_key = tuple(primary_key)
              self._log("Identified primary key columns: %s", primary_key)
  
          # determine cols that aren't expressed within our tables; mark these
          # as "read only" properties which are refreshed upon INSERT/UPDATE
          self._readonly_props = set(
              self._columntoproperty[col]
              for col in self._columntoproperty
              if self._columntoproperty[col] not in self._identity_key_props and
              (not hasattr(col, 'table') or
                  col.table not in self._cols_by_table))
  
      def _configure_properties(self):
          # Column and other ClauseElement objects which are mapped
          self.columns = self.c = util.OrderedProperties()
  
          # object attribute names mapped to MapperProperty objects
          self._props = util.OrderedDict()
  
          # table columns mapped to lists of MapperProperty objects
          # using a list allows a single column to be defined as
          # populating multiple object attributes
          self._columntoproperty = _ColumnMapping(self)
  
          # load custom properties
          if self._init_properties:
              for key, prop in self._init_properties.items():
                  self._configure_property(key, prop, False)
  
          # pull properties from the inherited mapper if any.
          if self.inherits:
              for key, prop in self.inherits._props.items():
                  if key not in self._props and \
                      not self._should_exclude(key, key, local=False,
                                               column=None):
                      self._adapt_inherited_property(key, prop, False)
  
          # create properties for each column in the mapped table,
          # for those columns which don't already map to a property
          for column in self.mapped_table.columns:
              if column in self._columntoproperty:
                  continue
  
              column_key = (self.column_prefix or '') + column.key
  
              if self._should_exclude(
                  column.key, column_key,
                  local=self.local_table.c.contains_column(column),
                  column=column
              ):
                  continue
  
              # adjust the "key" used for this column to that
              # of the inheriting mapper
              for mapper in self.iterate_to_root():
                  if column in mapper._columntoproperty:
                      column_key = mapper._columntoproperty[column].key
  
              self._configure_property(column_key,
                                       column,
                                       init=False,
                                       setparent=True)
  
      def _configure_polymorphic_setter(self, init=False):
          """Configure an attribute on the mapper representing the
          'polymorphic_on' column, if applicable, and not
          already generated by _configure_properties (which is typical).
  
          Also create a setter function which will assign this
          attribute to the value of the 'polymorphic_identity'
          upon instance construction, also if applicable.  This
          routine will run when an instance is created.
  
          """
          setter = False
  
          if self.polymorphic_on is not None:
              setter = True
  
              if isinstance(self.polymorphic_on, util.string_types):
                  # polymorphic_on specified as a string - link
                  # it to mapped ColumnProperty
                  try:
                      self.polymorphic_on = self._props[self.polymorphic_on]
                  except KeyError:
                      raise sa_exc.ArgumentError(
                          "Can't determine polymorphic_on "
                          "value '%s' - no attribute is "
                          "mapped to this name." % self.polymorphic_on)
  
              if self.polymorphic_on in self._columntoproperty:
                  # polymorphic_on is a column that is already mapped
                  # to a ColumnProperty
                  prop = self._columntoproperty[self.polymorphic_on]
              elif isinstance(self.polymorphic_on, MapperProperty):
                  # polymorphic_on is directly a MapperProperty,
                  # ensure it's a ColumnProperty
                  if not isinstance(self.polymorphic_on,
                                    properties.ColumnProperty):
                      raise sa_exc.ArgumentError(
                          "Only direct column-mapped "
                          "property or SQL expression "
                          "can be passed for polymorphic_on")
                  prop = self.polymorphic_on
              elif not expression._is_column(self.polymorphic_on):
                  # polymorphic_on is not a Column and not a ColumnProperty;
                  # not supported right now.
                  raise sa_exc.ArgumentError(
                      "Only direct column-mapped "
                      "property or SQL expression "
                      "can be passed for polymorphic_on"
                  )
              else:
                  # polymorphic_on is a Column or SQL expression and
                  # doesn't appear to be mapped. this means it can be 1.
                  # only present in the with_polymorphic selectable or
                  # 2. a totally standalone SQL expression which we'd
                  # hope is compatible with this mapper's mapped_table
                  col = self.mapped_table.corresponding_column(
                      self.polymorphic_on)
                  if col is None:
                      # polymorphic_on doesn't derive from any
                      # column/expression isn't present in the mapped
                      # table. we will make a "hidden" ColumnProperty
                      # for it. Just check that if it's directly a
                      # schema.Column and we have with_polymorphic, it's
                      # likely a user error if the schema.Column isn't
                      # represented somehow in either mapped_table or
                      # with_polymorphic.   Otherwise as of 0.7.4 we
                      # just go with it and assume the user wants it
                      # that way (i.e. a CASE statement)
                      setter = False
                      instrument = False
                      col = self.polymorphic_on
                      if isinstance(col, schema.Column) and (
                              self.with_polymorphic is None or
                              self.with_polymorphic[1].
                              corresponding_column(col) is None):
                          raise sa_exc.InvalidRequestError(
                              "Could not map polymorphic_on column "
                              "'%s' to the mapped table - polymorphic "
                              "loads will not function properly"
                              % col.description)
                  else:
                      # column/expression that polymorphic_on derives from
                      # is present in our mapped table
                      # and is probably mapped, but polymorphic_on itself
                      # is not.  This happens when
                      # the polymorphic_on is only directly present in the
                      # with_polymorphic selectable, as when use
                      # polymorphic_union.
                      # we'll make a separate ColumnProperty for it.
                      instrument = True
                  key = getattr(col, 'key', None)
                  if key:
                      if self._should_exclude(col.key, col.key, False, col):
                          raise sa_exc.InvalidRequestError(
                              "Cannot exclude or override the "
                              "discriminator column %r" %
                              col.key)
                  else:
                      self.polymorphic_on = col = \
                          col.label("_sa_polymorphic_on")
                      key = col.key
  
                  prop = properties.ColumnProperty(col, _instrument=instrument)
                  self._configure_property(key, prop, init=init, setparent=True)
  
              # the actual polymorphic_on should be the first public-facing
              # column in the property
              self.polymorphic_on = prop.columns[0]
              polymorphic_key = prop.key
  
          else:
              # no polymorphic_on was set.
              # check inheriting mappers for one.
              for mapper in self.iterate_to_root():
                  # determine if polymorphic_on of the parent
                  # should be propagated here.   If the col
                  # is present in our mapped table, or if our mapped
                  # table is the same as the parent (i.e. single table
                  # inheritance), we can use it
                  if mapper.polymorphic_on is not None:
                      if self.mapped_table is mapper.mapped_table:
                          self.polymorphic_on = mapper.polymorphic_on
                      else:
                          self.polymorphic_on = \
                              self.mapped_table.corresponding_column(
                                  mapper.polymorphic_on)
                      # we can use the parent mapper's _set_polymorphic_identity
                      # directly; it ensures the polymorphic_identity of the
                      # instance's mapper is used so is portable to subclasses.
                      if self.polymorphic_on is not None:
                          self._set_polymorphic_identity = \
                              mapper._set_polymorphic_identity
                          self._validate_polymorphic_identity = \
                              mapper._validate_polymorphic_identity
                      else:
                          self._set_polymorphic_identity = None
                      return
  
          if setter:
              def _set_polymorphic_identity(state):
                  dict_ = state.dict
                  state.get_impl(polymorphic_key).set(
                      state, dict_,
                      state.manager.mapper.polymorphic_identity,
                      None)
  
              def _validate_polymorphic_identity(mapper, state, dict_):
                  if polymorphic_key in dict_ and \
                          dict_[polymorphic_key] not in \
                          mapper._acceptable_polymorphic_identities:
                      util.warn_limited(
                          "Flushing object %s with "
                          "incompatible polymorphic identity %r; the "
                          "object may not refresh and/or load correctly",
                          (state_str(state), dict_[polymorphic_key])
                      )
  
              self._set_polymorphic_identity = _set_polymorphic_identity
              self._validate_polymorphic_identity = \
                  _validate_polymorphic_identity
          else:
              self._set_polymorphic_identity = None
  
      _validate_polymorphic_identity = None
  
      @_memoized_configured_property
      def _version_id_prop(self):
          if self.version_id_col is not None:
              return self._columntoproperty[self.version_id_col]
          else:
              return None
  
      @_memoized_configured_property
      def _acceptable_polymorphic_identities(self):
          identities = set()
  
          stack = deque([self])
          while stack:
              item = stack.popleft()
              if item.mapped_table is self.mapped_table:
                  identities.add(item.polymorphic_identity)
                  stack.extend(item._inheriting_mappers)
  
          return identities
  
      @_memoized_configured_property
      def _prop_set(self):
          return frozenset(self._props.values())
  
      def _adapt_inherited_property(self, key, prop, init):
          if not self.concrete:
              self._configure_property(key, prop, init=False, setparent=False)
          elif key not in self._props:
              self._configure_property(
                  key,
                  properties.ConcreteInheritedProperty(),
                  init=init, setparent=True)
  
      def _configure_property(self, key, prop, init=True, setparent=True):
          self._log("_configure_property(%s, %s)", key, prop.__class__.__name__)
  
          if not isinstance(prop, MapperProperty):
              prop = self._property_from_column(key, prop)
  
          if isinstance(prop, properties.ColumnProperty):
              col = self.mapped_table.corresponding_column(prop.columns[0])
  
              # if the column is not present in the mapped table,
              # test if a column has been added after the fact to the
              # parent table (or their parent, etc.) [ticket:1570]
              if col is None and self.inherits:
                  path = [self]
                  for m in self.inherits.iterate_to_root():
                      col = m.local_table.corresponding_column(prop.columns[0])
                      if col is not None:
                          for m2 in path:
                              m2.mapped_table._reset_exported()
                          col = self.mapped_table.corresponding_column(
                              prop.columns[0])
                          break
                      path.append(m)
  
              # subquery expression, column not present in the mapped
              # selectable.
              if col is None:
                  col = prop.columns[0]
  
                  # column is coming in after _readonly_props was
                  # initialized; check for 'readonly'
                  if hasattr(self, '_readonly_props') and \
                      (not hasattr(col, 'table') or
                          col.table not in self._cols_by_table):
                      self._readonly_props.add(prop)
  
              else:
                  # if column is coming in after _cols_by_table was
                  # initialized, ensure the col is in the right set
                  if hasattr(self, '_cols_by_table') and \
                          col.table in self._cols_by_table and \
                          col not in self._cols_by_table[col.table]:
                      self._cols_by_table[col.table].add(col)
  
              # if this properties.ColumnProperty represents the "polymorphic
              # discriminator" column, mark it.  We'll need this when rendering
              # columns in SELECT statements.
              if not hasattr(prop, '_is_polymorphic_discriminator'):
                  prop._is_polymorphic_discriminator = \
                      (col is self.polymorphic_on or
                       prop.columns[0] is self.polymorphic_on)
  
              self.columns[key] = col
              for col in prop.columns + prop._orig_columns:
                  for col in col.proxy_set:
                      self._columntoproperty[col] = prop
  
          prop.key = key
  
          if setparent:
              prop.set_parent(self, init)
  
          if key in self._props and \
                  getattr(self._props[key], '_mapped_by_synonym', False):
              syn = self._props[key]._mapped_by_synonym
              raise sa_exc.ArgumentError(
                  "Can't call map_column=True for synonym %r=%r, "
                  "a ColumnProperty already exists keyed to the name "
                  "%r for column %r" % (syn, key, key, syn)
              )
  
          if key in self._props and \
                  not isinstance(prop, properties.ColumnProperty) and \
                  not isinstance(
                      self._props[key],
                      (
                          properties.ColumnProperty,
                          properties.ConcreteInheritedProperty)
                  ):
              util.warn("Property %s on %s being replaced with new "
                        "property %s; the old property will be discarded" % (
                            self._props[key],
                            self,
                            prop,
                        ))
              oldprop = self._props[key]
              self._path_registry.pop(oldprop, None)
  
          self._props[key] = prop
  
          if not self.non_primary:
              prop.instrument_class(self)
  
          for mapper in self._inheriting_mappers:
              mapper._adapt_inherited_property(key, prop, init)
  
          if init:
              prop.init()
              prop.post_instrument_class(self)
  
          if self.configured:
              self._expire_memoizations()
  
      def _property_from_column(self, key, prop):
          """generate/update a :class:`.ColumnProprerty` given a
          :class:`.Column` object. """
  
          # we were passed a Column or a list of Columns;
          # generate a properties.ColumnProperty
          columns = util.to_list(prop)
          column = columns[0]
          if not expression._is_column(column):
              raise sa_exc.ArgumentError(
                  "%s=%r is not an instance of MapperProperty or Column"
                  % (key, prop))
  
          prop = self._props.get(key, None)
  
          if isinstance(prop, properties.ColumnProperty):
              if (
                  not self._inherits_equated_pairs or
                  (prop.columns[0], column) not in self._inherits_equated_pairs
              ) and \
                      not prop.columns[0].shares_lineage(column) and \
                      prop.columns[0] is not self.version_id_col and \
                      column is not self.version_id_col:
                  warn_only = prop.parent is not self
                  msg = ("Implicitly combining column %s with column "
                         "%s under attribute '%s'.  Please configure one "
                         "or more attributes for these same-named columns "
                         "explicitly." % (prop.columns[-1], column, key))
                  if warn_only:
                      util.warn(msg)
                  else:
                      raise sa_exc.InvalidRequestError(msg)
  
              # existing properties.ColumnProperty from an inheriting
              # mapper. make a copy and append our column to it
              prop = prop.copy()
              prop.columns.insert(0, column)
              self._log("inserting column to existing list "
                        "in properties.ColumnProperty %s" % (key))
              return prop
          elif prop is None or isinstance(prop,
                                          properties.ConcreteInheritedProperty):
              mapped_column = []
              for c in columns:
                  mc = self.mapped_table.corresponding_column(c)
                  if mc is None:
                      mc = self.local_table.corresponding_column(c)
                      if mc is not None:
                          # if the column is in the local table but not the
                          # mapped table, this corresponds to adding a
                          # column after the fact to the local table.
                          # [ticket:1523]
                          self.mapped_table._reset_exported()
                      mc = self.mapped_table.corresponding_column(c)
                      if mc is None:
                          raise sa_exc.ArgumentError(
                              "When configuring property '%s' on %s, "
                              "column '%s' is not represented in the mapper's "
                              "table. Use the `column_property()` function to "
                              "force this column to be mapped as a read-only "
                              "attribute." % (key, self, c))
                  mapped_column.append(mc)
              return properties.ColumnProperty(*mapped_column)
          else:
              raise sa_exc.ArgumentError(
                  "WARNING: when configuring property '%s' on %s, "
                  "column '%s' conflicts with property '%r'. "
                  "To resolve this, map the column to the class under a "
                  "different name in the 'properties' dictionary.  Or, "
                  "to remove all awareness of the column entirely "
                  "(including its availability as a foreign key), "
                  "use the 'include_properties' or 'exclude_properties' "
                  "mapper arguments to control specifically which table "
                  "columns get mapped." %
                  (key, self, column.key, prop))
  
      def _post_configure_properties(self):
          """Call the ``init()`` method on all ``MapperProperties``
          attached to this mapper.
  
          This is a deferred configuration step which is intended
          to execute once all mappers have been constructed.
  
          """
  
          self._log("_post_configure_properties() started")
          l = [(key, prop) for key, prop in self._props.items()]
          for key, prop in l:
              self._log("initialize prop %s", key)
  
              if prop.parent is self and not prop._configure_started:
                  prop.init()
  
              if prop._configure_finished:
                  prop.post_instrument_class(self)
  
          self._log("_post_configure_properties() complete")
          self.configured = True
  
      def add_properties(self, dict_of_properties):
          """Add the given dictionary of properties to this mapper,
          using `add_property`.
  
          """
          for key, value in dict_of_properties.items():
              self.add_property(key, value)
  
      def add_property(self, key, prop):
          """Add an individual MapperProperty to this mapper.
  
          If the mapper has not been configured yet, just adds the
          property to the initial properties dictionary sent to the
          constructor.  If this Mapper has already been configured, then
          the given MapperProperty is configured immediately.
  
          """
          self._init_properties[key] = prop
          self._configure_property(key, prop, init=self.configured)
  
      def _expire_memoizations(self):
          for mapper in self.iterate_to_root():
              _memoized_configured_property.expire_instance(mapper)
  
      @property
      def _log_desc(self):
          return "(" + self.class_.__name__ + \
              "|" + \
              (self.local_table is not None and
                  self.local_table.description or
                  str(self.local_table)) +\
              (self.non_primary and
               "|non-primary" or "") + ")"
  
      def _log(self, msg, *args):
          self.logger.info(
              "%s " + msg, *((self._log_desc,) + args)
          )
  
      def _log_debug(self, msg, *args):
          self.logger.debug(
              "%s " + msg, *((self._log_desc,) + args)
          )
  
      def __repr__(self):
          return '<Mapper at 0x%x; %s>' % (
              id(self), self.class_.__name__)
  
      def __str__(self):
          return "Mapper|%s|%s%s" % (
              self.class_.__name__,
              self.local_table is not None and
              self.local_table.description or None,
              self.non_primary and "|non-primary" or ""
          )
  
      def _is_orphan(self, state):
          orphan_possible = False
          for mapper in self.iterate_to_root():
              for (key, cls) in mapper._delete_orphans:
                  orphan_possible = True
  
                  has_parent = attributes.manager_of_class(cls).has_parent(
                      state, key, optimistic=state.has_identity)
  
                  if self.legacy_is_orphan and has_parent:
                      return False
                  elif not self.legacy_is_orphan and not has_parent:
                      return True
  
          if self.legacy_is_orphan:
              return orphan_possible
          else:
              return False
  
      def has_property(self, key):
          return key in self._props
  
      def get_property(self, key, _configure_mappers=True):
          """return a MapperProperty associated with the given key.
          """
  
          if _configure_mappers and Mapper._new_mappers:
              configure_mappers()
  
          try:
              return self._props[key]
          except KeyError:
              raise sa_exc.InvalidRequestError(
                  "Mapper '%s' has no property '%s'" % (self, key))
  
      def get_property_by_column(self, column):
          """Given a :class:`.Column` object, return the
          :class:`.MapperProperty` which maps this column."""
  
          return self._columntoproperty[column]
  
      @property
      def iterate_properties(self):
          """return an iterator of all MapperProperty objects."""
          if Mapper._new_mappers:
              configure_mappers()
          return iter(self._props.values())
  
      def _mappers_from_spec(self, spec, selectable):
          """given a with_polymorphic() argument, return the set of mappers it
          represents.
  
          Trims the list of mappers to just those represented within the given
          selectable, if present. This helps some more legacy-ish mappings.
  
          """
          if spec == '*':
              mappers = list(self.self_and_descendants)
          elif spec:
              mappers = set()
              for m in util.to_list(spec):
                  m = _class_to_mapper(m)
                  if not m.isa(self):
                      raise sa_exc.InvalidRequestError(
                          "%r does not inherit from %r" %
                          (m, self))
  
                  if selectable is None:
                      mappers.update(m.iterate_to_root())
                  else:
                      mappers.add(m)
              mappers = [m for m in self.self_and_descendants if m in mappers]
          else:
              mappers = []
  
          if selectable is not None:
              tables = set(sql_util.find_tables(selectable,
                                                include_aliases=True))
              mappers = [m for m in mappers if m.local_table in tables]
          return mappers
  
      def _selectable_from_mappers(self, mappers, innerjoin):
          """given a list of mappers (assumed to be within this mapper's
          inheritance hierarchy), construct an outerjoin amongst those mapper's
          mapped tables.
  
          """
          from_obj = self.mapped_table
          for m in mappers:
              if m is self:
                  continue
              if m.concrete:
                  raise sa_exc.InvalidRequestError(
                      "'with_polymorphic()' requires 'selectable' argument "
                      "when concrete-inheriting mappers are used.")
              elif not m.single:
                  if innerjoin:
                      from_obj = from_obj.join(m.local_table,
                                               m.inherit_condition)
                  else:
                      from_obj = from_obj.outerjoin(m.local_table,
                                                    m.inherit_condition)
  
          return from_obj
  
      @_memoized_configured_property
      def _single_table_criterion(self):
          if self.single and \
                  self.inherits and \
                  self.polymorphic_on is not None:
              return self.polymorphic_on.in_(
                  m.polymorphic_identity
                  for m in self.self_and_descendants)
          else:
              return None
  
      @_memoized_configured_property
      def _with_polymorphic_mappers(self):
          if Mapper._new_mappers:
              configure_mappers()
          if not self.with_polymorphic:
              return []
          return self._mappers_from_spec(*self.with_polymorphic)
  
      @_memoized_configured_property
      def _with_polymorphic_selectable(self):
          if not self.with_polymorphic:
              return self.mapped_table
  
          spec, selectable = self.with_polymorphic
          if selectable is not None:
              return selectable
          else:
              return self._selectable_from_mappers(
                  self._mappers_from_spec(spec, selectable),
                  False)
  
      with_polymorphic_mappers = _with_polymorphic_mappers
      """The list of :class:`.Mapper` objects included in the
      default "polymorphic" query.
  
      """
  
      @_memoized_configured_property
      def _insert_cols_evaluating_none(self):
          return dict(
              (
                  table,
                  frozenset(
                      col.key for col in columns
                      if col.type.should_evaluate_none
                  )
              )
              for table, columns in self._cols_by_table.items()
          )
  
      @_memoized_configured_property
      def _insert_cols_as_none(self):
          return dict(
              (
                  table,
                  frozenset(
                      col.key for col in columns
                      if not col.primary_key and
                      not col.server_default and not col.default
                      and not col.type.should_evaluate_none)
              )
              for table, columns in self._cols_by_table.items()
          )
  
      @_memoized_configured_property
      def _propkey_to_col(self):
          return dict(
              (
                  table,
                  dict(
                      (self._columntoproperty[col].key, col)
                      for col in columns
                  )
              )
              for table, columns in self._cols_by_table.items()
          )
  
      @_memoized_configured_property
      def _pk_keys_by_table(self):
          return dict(
              (
                  table,
                  frozenset([col.key for col in pks])
              )
              for table, pks in self._pks_by_table.items()
          )
  
      @_memoized_configured_property
      def _pk_attr_keys_by_table(self):
          return dict(
              (
                  table,
                  frozenset([self._columntoproperty[col].key for col in pks])
              )
              for table, pks in self._pks_by_table.items()
          )
  
      @_memoized_configured_property
      def _server_default_cols(self):
          return dict(
              (
                  table,
                  frozenset([
                      col.key for col in columns
                      if col.server_default is not None])
              )
              for table, columns in self._cols_by_table.items()
          )
  
      @_memoized_configured_property
      def _server_default_plus_onupdate_propkeys(self):
          result = set()
  
          for table, columns in self._cols_by_table.items():
              for col in columns:
                  if (
                          (
                              col.server_default is not None or
                              col.server_onupdate is not None
                          ) and col in self._columntoproperty
                  ):
                      result.add(self._columntoproperty[col].key)
  
          return result
  
      @_memoized_configured_property
      def _server_onupdate_default_cols(self):
          return dict(
              (
                  table,
                  frozenset([
                      col.key for col in columns
                      if col.server_onupdate is not None])
              )
              for table, columns in self._cols_by_table.items()
          )
  
      @property
      def selectable(self):
          """The :func:`.select` construct this :class:`.Mapper` selects from
          by default.
  
          Normally, this is equivalent to :attr:`.mapped_table`, unless
          the ``with_polymorphic`` feature is in use, in which case the
          full "polymorphic" selectable is returned.
  
          """
          return self._with_polymorphic_selectable
  
      def _with_polymorphic_args(self, spec=None, selectable=False,
                                 innerjoin=False):
          if self.with_polymorphic:
              if not spec:
                  spec = self.with_polymorphic[0]
              if selectable is False:
                  selectable = self.with_polymorphic[1]
          elif selectable is False:
              selectable = None
          mappers = self._mappers_from_spec(spec, selectable)
          if selectable is not None:
              return mappers, selectable
          else:
              return mappers, self._selectable_from_mappers(mappers,
                                                            innerjoin)
  
      @_memoized_configured_property
      def _polymorphic_properties(self):
          return list(self._iterate_polymorphic_properties(
              self._with_polymorphic_mappers))
  
      def _iterate_polymorphic_properties(self, mappers=None):
          """Return an iterator of MapperProperty objects which will render into
          a SELECT."""
          if mappers is None:
              mappers = self._with_polymorphic_mappers
  
          if not mappers:
              for c in self.iterate_properties:
                  yield c
          else:
              # in the polymorphic case, filter out discriminator columns
              # from other mappers, as these are sometimes dependent on that
              # mapper's polymorphic selectable (which we don't want rendered)
              for c in util.unique_list(
                  chain(*[
                      list(mapper.iterate_properties) for mapper in
                      [self] + mappers
                  ])
              ):
                  if getattr(c, '_is_polymorphic_discriminator', False) and \
                          (self.polymorphic_on is None or
                           c.columns[0] is not self.polymorphic_on):
                      continue
                  yield c
  
      @_memoized_configured_property
      def attrs(self):
          """A namespace of all :class:`.MapperProperty` objects
          associated this mapper.
  
          This is an object that provides each property based on
          its key name.  For instance, the mapper for a
          ``User`` class which has ``User.name`` attribute would
          provide ``mapper.attrs.name``, which would be the
          :class:`.ColumnProperty` representing the ``name``
          column.   The namespace object can also be iterated,
          which would yield each :class:`.MapperProperty`.
  
          :class:`.Mapper` has several pre-filtered views
          of this attribute which limit the types of properties
          returned, inclding :attr:`.synonyms`, :attr:`.column_attrs`,
          :attr:`.relationships`, and :attr:`.composites`.
  
          .. warning::
  
              The :attr:`.Mapper.attrs` accessor namespace is an
              instance of :class:`.OrderedProperties`.  This is
              a dictionary-like object which includes a small number of
              named methods such as :meth:`.OrderedProperties.items`
              and :meth:`.OrderedProperties.values`.  When
              accessing attributes dynamically, favor using the dict-access
              scheme, e.g. ``mapper.attrs[somename]`` over
              ``getattr(mapper.attrs, somename)`` to avoid name collisions.
  
          .. seealso::
  
              :attr:`.Mapper.all_orm_descriptors`
  
          """
          if Mapper._new_mappers:
              configure_mappers()
          return util.ImmutableProperties(self._props)
  
      @_memoized_configured_property
      def all_orm_descriptors(self):
          """A namespace of all :class:`.InspectionAttr` attributes associated
          with the mapped class.
  
          These attributes are in all cases Python :term:`descriptors`
          associated with the mapped class or its superclasses.
  
          This namespace includes attributes that are mapped to the class
          as well as attributes declared by extension modules.
          It includes any Python descriptor type that inherits from
          :class:`.InspectionAttr`.  This includes
          :class:`.QueryableAttribute`, as well as extension types such as
          :class:`.hybrid_property`, :class:`.hybrid_method` and
          :class:`.AssociationProxy`.
  
          To distinguish between mapped attributes and extension attributes,
          the attribute :attr:`.InspectionAttr.extension_type` will refer
          to a constant that distinguishes between different extension types.
  
          When dealing with a :class:`.QueryableAttribute`, the
          :attr:`.QueryableAttribute.property` attribute refers to the
          :class:`.MapperProperty` property, which is what you get when
          referring to the collection of mapped properties via
          :attr:`.Mapper.attrs`.
  
          .. warning::
  
              The :attr:`.Mapper.all_orm_descriptors` accessor namespace is an
              instance of :class:`.OrderedProperties`.  This is
              a dictionary-like object which includes a small number of
              named methods such as :meth:`.OrderedProperties.items`
              and :meth:`.OrderedProperties.values`.  When
              accessing attributes dynamically, favor using the dict-access
              scheme, e.g. ``mapper.all_orm_descriptors[somename]`` over
              ``getattr(mapper.all_orm_descriptors, somename)`` to avoid name
              collisions.
  
          .. versionadded:: 0.8.0
  
          .. seealso::
  
              :attr:`.Mapper.attrs`
  
          """
          return util.ImmutableProperties(
              dict(self.class_manager._all_sqla_attributes()))
  
      @_memoized_configured_property
      def synonyms(self):
          """Return a namespace of all :class:`.SynonymProperty`
          properties maintained by this :class:`.Mapper`.
  
          .. seealso::
  
              :attr:`.Mapper.attrs` - namespace of all :class:`.MapperProperty`
              objects.
  
          """
          return self._filter_properties(properties.SynonymProperty)
  
      @_memoized_configured_property
      def column_attrs(self):
          """Return a namespace of all :class:`.ColumnProperty`
          properties maintained by this :class:`.Mapper`.
  
          .. seealso::
  
              :attr:`.Mapper.attrs` - namespace of all :class:`.MapperProperty`
              objects.
  
          """
          return self._filter_properties(properties.ColumnProperty)
  
      @_memoized_configured_property
      def relationships(self):
          """A namespace of all :class:`.RelationshipProperty` properties
          maintained by this :class:`.Mapper`.
  
          .. warning::
  
              the :attr:`.Mapper.relationships` accessor namespace is an
              instance of :class:`.OrderedProperties`.  This is
              a dictionary-like object which includes a small number of
              named methods such as :meth:`.OrderedProperties.items`
              and :meth:`.OrderedProperties.values`.  When
              accessing attributes dynamically, favor using the dict-access
              scheme, e.g. ``mapper.relationships[somename]`` over
              ``getattr(mapper.relationships, somename)`` to avoid name
              collisions.
  
          .. seealso::
  
              :attr:`.Mapper.attrs` - namespace of all :class:`.MapperProperty`
              objects.
  
          """
          return self._filter_properties(properties.RelationshipProperty)
  
      @_memoized_configured_property
      def composites(self):
          """Return a namespace of all :class:`.CompositeProperty`
          properties maintained by this :class:`.Mapper`.
  
          .. seealso::
  
              :attr:`.Mapper.attrs` - namespace of all :class:`.MapperProperty`
              objects.
  
          """
          return self._filter_properties(properties.CompositeProperty)
  
      def _filter_properties(self, type_):
          if Mapper._new_mappers:
              configure_mappers()
          return util.ImmutableProperties(util.OrderedDict(
              (k, v) for k, v in self._props.items()
              if isinstance(v, type_)
          ))
  
      @_memoized_configured_property
      def _get_clause(self):
          """create a "get clause" based on the primary key.  this is used
          by query.get() and many-to-one lazyloads to load this item
          by primary key.
  
          """
          params = [(primary_key, sql.bindparam(None, type_=primary_key.type))
                    for primary_key in self.primary_key]
          return sql.and_(*[k == v for (k, v) in params]), \
              util.column_dict(params)
  
      @_memoized_configured_property
      def _equivalent_columns(self):
          """Create a map of all *equivalent* columns, based on
          the determination of column pairs that are equated to
          one another based on inherit condition.  This is designed
          to work with the queries that util.polymorphic_union
          comes up with, which often don't include the columns from
          the base table directly (including the subclass table columns
          only).
  
          The resulting structure is a dictionary of columns mapped
          to lists of equivalent columns, i.e.
  
          {
              tablea.col1:
                  set([tableb.col1, tablec.col1]),
              tablea.col2:
                  set([tabled.col2])
          }
  
          """
          result = util.column_dict()
  
          def visit_binary(binary):
              if binary.operator == operators.eq:
                  if binary.left in result:
                      result[binary.left].add(binary.right)
                  else:
                      result[binary.left] = util.column_set((binary.right,))
                  if binary.right in result:
                      result[binary.right].add(binary.left)
                  else:
                      result[binary.right] = util.column_set((binary.left,))
          for mapper in self.base_mapper.self_and_descendants:
              if mapper.inherit_condition is not None:
                  visitors.traverse(
                      mapper.inherit_condition, {},
                      {'binary': visit_binary})
  
          return result
  
      def _is_userland_descriptor(self, obj):
          if isinstance(obj, (_MappedAttribute,
                              instrumentation.ClassManager,
                              expression.ColumnElement)):
              return False
          else:
              return True
  
      def _should_exclude(self, name, assigned_name, local, column):
          """determine whether a particular property should be implicitly
          present on the class.
  
          This occurs when properties are propagated from an inherited class, or
          are applied from the columns present in the mapped table.
  
          """
  
          # check for class-bound attributes and/or descriptors,
          # either local or from an inherited class
          if local:
              if self.class_.__dict__.get(assigned_name, None) is not None \
                      and self._is_userland_descriptor(
                      self.class_.__dict__[assigned_name]):
                  return True
          else:
              if getattr(self.class_, assigned_name, None) is not None \
                      and self._is_userland_descriptor(
                      getattr(self.class_, assigned_name)):
                  return True
  
          if self.include_properties is not None and \
                  name not in self.include_properties and \
                  (column is None or column not in self.include_properties):
              self._log("not including property %s" % (name))
              return True
  
          if self.exclude_properties is not None and \
                  (
                      name in self.exclude_properties or
                      (column is not None and column in self.exclude_properties)
                  ):
              self._log("excluding property %s" % (name))
              return True
  
          return False
  
      def common_parent(self, other):
          """Return true if the given mapper shares a
          common inherited parent as this mapper."""
  
          return self.base_mapper is other.base_mapper
  
      def _canload(self, state, allow_subtypes):
          s = self.primary_mapper()
          if self.polymorphic_on is not None or allow_subtypes:
              return _state_mapper(state).isa(s)
          else:
              return _state_mapper(state) is s
  
      def isa(self, other):
          """Return True if the this mapper inherits from the given mapper."""
  
          m = self
          while m and m is not other:
              m = m.inherits
          return bool(m)
  
      def iterate_to_root(self):
          m = self
          while m:
              yield m
              m = m.inherits
  
      @_memoized_configured_property
      def self_and_descendants(self):
          """The collection including this mapper and all descendant mappers.
  
          This includes not just the immediately inheriting mappers but
          all their inheriting mappers as well.
  
          """
          descendants = []
          stack = deque([self])
          while stack:
              item = stack.popleft()
              descendants.append(item)
              stack.extend(item._inheriting_mappers)
          return util.WeakSequence(descendants)
  
      def polymorphic_iterator(self):
          """Iterate through the collection including this mapper and
          all descendant mappers.
  
          This includes not just the immediately inheriting mappers but
          all their inheriting mappers as well.
  
          To iterate through an entire hierarchy, use
          ``mapper.base_mapper.polymorphic_iterator()``.
  
          """
          return iter(self.self_and_descendants)
  
      def primary_mapper(self):
          """Return the primary mapper corresponding to this mapper's class key
          (class)."""
  
          return self.class_manager.mapper
  
      @property
      def primary_base_mapper(self):
          return self.class_manager.mapper.base_mapper
  
      def _result_has_identity_key(self, result, adapter=None):
          pk_cols = self.primary_key
          if adapter:
              pk_cols = [adapter.columns[c] for c in pk_cols]
          for col in pk_cols:
              if not result._has_key(col):
                  return False
          else:
              return True
  
      def identity_key_from_row(self, row, adapter=None):
          """Return an identity-map key for use in storing/retrieving an
          item from the identity map.
  
          :param row: A :class:`.RowProxy` instance.  The columns which are
           mapped by this :class:`.Mapper` should be locatable in the row,
           preferably via the :class:`.Column` object directly (as is the case
           when a :func:`.select` construct is executed), or via string names of
           the form ``<tablename>_<colname>``.
  
          """
          pk_cols = self.primary_key
          if adapter:
              pk_cols = [adapter.columns[c] for c in pk_cols]
  
          return self._identity_class, \
              tuple(row[column] for column in pk_cols)
  
      def identity_key_from_primary_key(self, primary_key):
          """Return an identity-map key for use in storing/retrieving an
          item from an identity map.
  
          :param primary_key: A list of values indicating the identifier.
  
          """
          return self._identity_class, tuple(primary_key)
  
      def identity_key_from_instance(self, instance):
          """Return the identity key for the given instance, based on
          its primary key attributes.
  
          If the instance's state is expired, calling this method
          will result in a database check to see if the object has been deleted.
          If the row no longer exists,
          :class:`~sqlalchemy.orm.exc.ObjectDeletedError` is raised.
  
          This value is typically also found on the instance state under the
          attribute name `key`.
  
          """
          return self.identity_key_from_primary_key(
              self.primary_key_from_instance(instance))
  
      def _identity_key_from_state(self, state):
          dict_ = state.dict
          manager = state.manager
          return self._identity_class, tuple([
              manager[self._columntoproperty[col].key].
              impl.get(state, dict_, attributes.PASSIVE_RETURN_NEVER_SET)
              for col in self.primary_key
          ])
  
      def primary_key_from_instance(self, instance):
          """Return the list of primary key values for the given
          instance.
  
          If the instance's state is expired, calling this method
          will result in a database check to see if the object has been deleted.
          If the row no longer exists,
          :class:`~sqlalchemy.orm.exc.ObjectDeletedError` is raised.
  
          """
          state = attributes.instance_state(instance)
          return self._primary_key_from_state(state, attributes.PASSIVE_OFF)
  
      def _primary_key_from_state(
              self, state, passive=attributes.PASSIVE_RETURN_NEVER_SET):
          dict_ = state.dict
          manager = state.manager
          return [
              manager[prop.key].
              impl.get(state, dict_, passive)
              for prop in self._identity_key_props
          ]
  
      @_memoized_configured_property
      def _identity_key_props(self):
          return [self._columntoproperty[col] for col in self.primary_key]
  
      @_memoized_configured_property
      def _all_pk_props(self):
          collection = set()
          for table in self.tables:
              collection.update(self._pks_by_table[table])
          return collection
  
      @_memoized_configured_property
      def _should_undefer_in_wildcard(self):
          cols = set(self.primary_key)
          if self.polymorphic_on is not None:
              cols.add(self.polymorphic_on)
          return cols
  
      @_memoized_configured_property
      def _primary_key_propkeys(self):
          return set([prop.key for prop in self._all_pk_props])
  
      def _get_state_attr_by_column(
              self, state, dict_, column,
              passive=attributes.PASSIVE_RETURN_NEVER_SET):
          prop = self._columntoproperty[column]
          return state.manager[prop.key].impl.get(state, dict_, passive=passive)
  
      def _set_committed_state_attr_by_column(self, state, dict_, column, value):
          prop = self._columntoproperty[column]
          state.manager[prop.key].impl.set_committed_value(state, dict_, value)
  
      def _set_state_attr_by_column(self, state, dict_, column, value):
          prop = self._columntoproperty[column]
          state.manager[prop.key].impl.set(state, dict_, value, None)
  
      def _get_committed_attr_by_column(self, obj, column):
          state = attributes.instance_state(obj)
          dict_ = attributes.instance_dict(obj)
          return self._get_committed_state_attr_by_column(
              state, dict_, column, passive=attributes.PASSIVE_OFF)
  
      def _get_committed_state_attr_by_column(
              self, state, dict_, column,
              passive=attributes.PASSIVE_RETURN_NEVER_SET):
  
          prop = self._columntoproperty[column]
          return state.manager[prop.key].impl.\
              get_committed_value(state, dict_, passive=passive)
  
      def _optimized_get_statement(self, state, attribute_names):
          """assemble a WHERE clause which retrieves a given state by primary
          key, using a minimized set of tables.
  
          Applies to a joined-table inheritance mapper where the
          requested attribute names are only present on joined tables,
          not the base table.  The WHERE clause attempts to include
          only those tables to minimize joins.
  
          """
          props = self._props
  
          tables = set(chain(
              *[sql_util.find_tables(c, check_columns=True)
                for key in attribute_names
                for c in props[key].columns]
          ))
  
          if self.base_mapper.local_table in tables:
              return None
  
          class ColumnsNotAvailable(Exception):
              pass
  
          def visit_binary(binary):
              leftcol = binary.left
              rightcol = binary.right
              if leftcol is None or rightcol is None:
                  return
  
              if leftcol.table not in tables:
                  leftval = self._get_committed_state_attr_by_column(
                      state, state.dict,
                      leftcol,
                      passive=attributes.PASSIVE_NO_INITIALIZE)
                  if leftval in orm_util._none_set:
                      raise ColumnsNotAvailable()
                  binary.left = sql.bindparam(None, leftval,
                                              type_=binary.right.type)
              elif rightcol.table not in tables:
                  rightval = self._get_committed_state_attr_by_column(
                      state, state.dict,
                      rightcol,
                      passive=attributes.PASSIVE_NO_INITIALIZE)
                  if rightval in orm_util._none_set:
                      raise ColumnsNotAvailable()
                  binary.right = sql.bindparam(None, rightval,
                                               type_=binary.right.type)
  
          allconds = []
  
          try:
              start = False
              for mapper in reversed(list(self.iterate_to_root())):
                  if mapper.local_table in tables:
                      start = True
                  elif not isinstance(mapper.local_table,
                                      expression.TableClause):
                      return None
                  if start and not mapper.single:
                      allconds.append(visitors.cloned_traverse(
                          mapper.inherit_condition,
                          {},
                          {'binary': visit_binary}
                      )
                      )
          except ColumnsNotAvailable:
              return None
  
          cond = sql.and_(*allconds)
  
          cols = []
          for key in attribute_names:
              cols.extend(props[key].columns)
          return sql.select(cols, cond, use_labels=True)
  
      def cascade_iterator(self, type_, state, halt_on=None):
          """Iterate each element and its mapper in an object graph,
          for all relationships that meet the given cascade rule.
  
          :param type_:
            The name of the cascade rule (i.e. ``"save-update"``, ``"delete"``,
            etc.).
  
            .. note::  the ``"all"`` cascade is not accepted here.  For a generic
               object traversal function, see :ref:`faq_walk_objects`.
  
          :param state:
            The lead InstanceState.  child items will be processed per
            the relationships defined for this object's mapper.
  
          :return: the method yields individual object instances.
  
          .. seealso::
  
              :ref:`unitofwork_cascades`
  
              :ref:`faq_walk_objects` - illustrates a generic function to
              traverse all objects without relying on cascades.
  
          """
          visited_states = set()
          prp, mpp = object(), object()
  
          visitables = deque([(deque(self._props.values()), prp,
                               state, state.dict)])
  
          while visitables:
              iterator, item_type, parent_state, parent_dict = visitables[-1]
              if not iterator:
                  visitables.pop()
                  continue
  
              if item_type is prp:
                  prop = iterator.popleft()
                  if type_ not in prop.cascade:
                      continue
                  queue = deque(prop.cascade_iterator(
                      type_, parent_state, parent_dict,
                      visited_states, halt_on))
                  if queue:
                      visitables.append((queue, mpp, None, None))
              elif item_type is mpp:
                  instance, instance_mapper, corresponding_state, \
                      corresponding_dict = iterator.popleft()
                  yield instance, instance_mapper, \
                      corresponding_state, corresponding_dict
                  visitables.append((deque(instance_mapper._props.values()),
                                     prp, corresponding_state,
                                     corresponding_dict))
  
      @_memoized_configured_property
      def _compiled_cache(self):
          return util.LRUCache(self._compiled_cache_size)
  
      @_memoized_configured_property
      def _sorted_tables(self):
          table_to_mapper = {}
  
          for mapper in self.base_mapper.self_and_descendants:
              for t in mapper.tables:
                  table_to_mapper.setdefault(t, mapper)
  
          extra_dependencies = []
          for table, mapper in table_to_mapper.items():
              super_ = mapper.inherits
              if super_:
                  extra_dependencies.extend([
                      (super_table, table)
                      for super_table in super_.tables
                  ])
  
          def skip(fk):
              # attempt to skip dependencies that are not
              # significant to the inheritance chain
              # for two tables that are related by inheritance.
              # while that dependency may be important, it's technically
              # not what we mean to sort on here.
              parent = table_to_mapper.get(fk.parent.table)
              dep = table_to_mapper.get(fk.column.table)
              if parent is not None and \
                  dep is not None and \
                  dep is not parent and \
                      dep.inherit_condition is not None:
                  cols = set(sql_util._find_columns(dep.inherit_condition))
                  if parent.inherit_condition is not None:
                      cols = cols.union(sql_util._find_columns(
                          parent.inherit_condition))
                      return fk.parent not in cols and fk.column not in cols
                  else:
                      return fk.parent not in cols
              return False
  
          sorted_ = sql_util.sort_tables(table_to_mapper,
                                         skip_fn=skip,
                                         extra_dependencies=extra_dependencies)
  
          ret = util.OrderedDict()
          for t in sorted_:
              ret[t] = table_to_mapper[t]
          return ret
  
      def _memo(self, key, callable_):
          if key in self._memoized_values:
              return self._memoized_values[key]
          else:
              self._memoized_values[key] = value = callable_()
              return value
  
      @util.memoized_property
      def _table_to_equated(self):
          """memoized map of tables to collections of columns to be
          synchronized upwards to the base mapper."""
  
          result = util.defaultdict(list)
  
          for table in self._sorted_tables:
              cols = set(table.c)
              for m in self.iterate_to_root():
                  if m._inherits_equated_pairs and \
                          cols.intersection(
                              util.reduce(set.union,
                                          [l.proxy_set for l, r in
                                           m._inherits_equated_pairs])
                          ):
                      result[table].append((m, m._inherits_equated_pairs))
  
          return result
  
  
  def configure_mappers():
      """Initialize the inter-mapper relationships of all mappers that
      have been constructed thus far.
  
      This function can be called any number of times, but in
      most cases is invoked automatically, the first time mappings are used,
      as well as whenever mappings are used and additional not-yet-configured
      mappers have been constructed.
  
      Points at which this occur include when a mapped class is instantiated
      into an instance, as well as when the :meth:`.Session.query` method
      is used.
  
      The :func:`.configure_mappers` function provides several event hooks
      that can be used to augment its functionality.  These methods include:
  
      * :meth:`.MapperEvents.before_configured` - called once before
        :func:`.configure_mappers` does any work; this can be used to establish
        additional options, properties, or related mappings before the operation
        proceeds.
  
      * :meth:`.MapperEvents.mapper_configured` - called as each indivudal
        :class:`.Mapper` is configured within the process; will include all
        mapper state except for backrefs set up by other mappers that are still
        to be configured.
  
      * :meth:`.MapperEvents.after_configured` - called once after
        :func:`.configure_mappers` is complete; at this stage, all
        :class:`.Mapper` objects that are known  to SQLAlchemy will be fully
        configured.  Note that the calling application may still have other
        mappings that haven't been produced yet, such as if they are in modules
        as yet unimported.
  
      """
  
      if not Mapper._new_mappers:
          return
  
      _CONFIGURE_MUTEX.acquire()
      try:
          global _already_compiling
          if _already_compiling:
              return
          _already_compiling = True
          try:
  
              # double-check inside mutex
              if not Mapper._new_mappers:
                  return
  
              Mapper.dispatch._for_class(Mapper).before_configured()
              # initialize properties on all mappers
              # note that _mapper_registry is unordered, which
              # may randomly conceal/reveal issues related to
              # the order of mapper compilation
  
              for mapper in list(_mapper_registry):
                  if getattr(mapper, '_configure_failed', False):
                      e = sa_exc.InvalidRequestError(
                          "One or more mappers failed to initialize - "
                          "can't proceed with initialization of other "
                          "mappers. Triggering mapper: '%s'. "
                          "Original exception was: %s"
                          % (mapper, mapper._configure_failed))
                      e._configure_failed = mapper._configure_failed
                      raise e
                  if not mapper.configured:
                      try:
                          mapper._post_configure_properties()
                          mapper._expire_memoizations()
                          mapper.dispatch.mapper_configured(
                              mapper, mapper.class_)
                      except Exception:
                          exc = sys.exc_info()[1]
                          if not hasattr(exc, '_configure_failed'):
                              mapper._configure_failed = exc
                          raise
  
              Mapper._new_mappers = False
          finally:
              _already_compiling = False
      finally:
          _CONFIGURE_MUTEX.release()
      Mapper.dispatch._for_class(Mapper).after_configured()
  
  
  def reconstructor(fn):
      """Decorate a method as the 'reconstructor' hook.
  
      Designates a method as the "reconstructor", an ``__init__``-like
      method that will be called by the ORM after the instance has been
      loaded from the database or otherwise reconstituted.
  
      The reconstructor will be invoked with no arguments.  Scalar
      (non-collection) database-mapped attributes of the instance will
      be available for use within the function.  Eagerly-loaded
      collections are generally not yet available and will usually only
      contain the first element.  ORM state changes made to objects at
      this stage will not be recorded for the next flush() operation, so
      the activity within a reconstructor should be conservative.
  
      """
      fn.__sa_reconstructor__ = True
      return fn
  
  
  def validates(*names, **kw):
      r"""Decorate a method as a 'validator' for one or more named properties.
  
      Designates a method as a validator, a method which receives the
      name of the attribute as well as a value to be assigned, or in the
      case of a collection, the value to be added to the collection.
      The function can then raise validation exceptions to halt the
      process from continuing (where Python's built-in ``ValueError``
      and ``AssertionError`` exceptions are reasonable choices), or can
      modify or replace the value before proceeding. The function should
      otherwise return the given value.
  
      Note that a validator for a collection **cannot** issue a load of that
      collection within the validation routine - this usage raises
      an assertion to avoid recursion overflows.  This is a reentrant
      condition which is not supported.
  
      :param \*names: list of attribute names to be validated.
      :param include_removes: if True, "remove" events will be
       sent as well - the validation function must accept an additional
       argument "is_remove" which will be a boolean.
  
       .. versionadded:: 0.7.7
      :param include_backrefs: defaults to ``True``; if ``False``, the
       validation function will not emit if the originator is an attribute
       event related via a backref.  This can be used for bi-directional
       :func:`.validates` usage where only one validator should emit per
       attribute operation.
  
       .. versionadded:: 0.9.0
  
      .. seealso::
  
        :ref:`simple_validators` - usage examples for :func:`.validates`
  
      """
      include_removes = kw.pop('include_removes', False)
      include_backrefs = kw.pop('include_backrefs', True)
  
      def wrap(fn):
          fn.__sa_validators__ = names
          fn.__sa_validation_opts__ = {
              "include_removes": include_removes,
              "include_backrefs": include_backrefs
          }
          return fn
      return wrap
  
  
  def _event_on_load(state, ctx):
      instrumenting_mapper = state.manager.info[_INSTRUMENTOR]
      if instrumenting_mapper._reconstructor:
          instrumenting_mapper._reconstructor(state.obj())
  
  
  def _event_on_first_init(manager, cls):
      """Initial mapper compilation trigger.
  
      instrumentation calls this one when InstanceState
      is first generated, and is needed for legacy mutable
      attributes to work.
      """
  
      instrumenting_mapper = manager.info.get(_INSTRUMENTOR)
      if instrumenting_mapper:
          if Mapper._new_mappers:
              configure_mappers()
  
  
  def _event_on_init(state, args, kwargs):
      """Run init_instance hooks.
  
      This also includes mapper compilation, normally not needed
      here but helps with some piecemeal configuration
      scenarios (such as in the ORM tutorial).
  
      """
  
      instrumenting_mapper = state.manager.info.get(_INSTRUMENTOR)
      if instrumenting_mapper:
          if Mapper._new_mappers:
              configure_mappers()
          if instrumenting_mapper._set_polymorphic_identity:
              instrumenting_mapper._set_polymorphic_identity(state)
  
  
  class _ColumnMapping(dict):
      """Error reporting helper for mapper._columntoproperty."""
  
      __slots__ = 'mapper',
  
      def __init__(self, mapper):
          self.mapper = mapper
  
      def __missing__(self, column):
          prop = self.mapper._props.get(column)
          if prop:
              raise orm_exc.UnmappedColumnError(
                  "Column '%s.%s' is not available, due to "
                  "conflicting property '%s':%r" % (
                      column.table.name, column.name, column.key, prop))
          raise orm_exc.UnmappedColumnError(
              "No column %s is configured on mapper %s..." %
              (column, self.mapper))
  