text: # orm/query.py
  # Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Michael Bayer mike_mp@zzzcomputing.com
  #
  # This module is part of SQLAlchemy and is released under
  # the MIT License: http://www.opensource.org/licenses/mit-license.php
  
  """The Query class and support.
  
  Defines the :class:`.Query` class, the central 
  construct used by the ORM to construct database queries.
  
  The :class:`.Query` class should not be confused with the
  :class:`.Select` class, which defines database 
  SELECT operations at the SQL (non-ORM) level.  ``Query`` differs from 
  ``Select`` in that it returns ORM-mapped objects and interacts with an 
  ORM session, whereas the ``Select`` construct interacts directly with the 
  database to return iterable result sets.
  
  """
  
  from itertools import chain
  from operator import itemgetter
  
  from sqlalchemy import sql, util, log, schema
  from sqlalchemy import exc as sa_exc
  from sqlalchemy.orm import exc as orm_exc
  from sqlalchemy.sql import util as sql_util
  from sqlalchemy.sql import expression, visitors, operators
  from sqlalchemy.orm import (
      attributes, interfaces, mapper, object_mapper, evaluator,
      )
  from sqlalchemy.orm.util import (
      AliasedClass, ORMAdapter, _entity_descriptor, _entity_info,
      _is_aliased_class, _is_mapped_class, _orm_columns, _orm_selectable,
      join as orm_join,with_parent
      )
  
  
  __all__ = ['Query', 'QueryContext', 'aliased']
  
  
  aliased = AliasedClass
  
  def _generative(*assertions):
      """Mark a method as generative."""
  
      @util.decorator
      def generate(fn, *args, **kw):
          self = args[0]._clone()
          for assertion in assertions:
              assertion(self, fn.func_name)
          fn(self, *args[1:], **kw)
          return self
      return generate
  
  class Query(object):
      """ORM-level SQL construction object.
      
      :class:`.Query` is the source of all SELECT statements generated by the
      ORM, both those formulated by end-user query operations as well as by 
      high level internal operations such as related collection loading.  It 
      features a generative interface whereby successive calls return a new
      :class:`.Query` object, a copy of the former with additional 
      criteria and options associated with it.
      
      :class:`.Query` objects are normally initially generated using the 
      :meth:`~.Session.query` method of :class:`.Session`.  For a full walkthrough 
      of :class:`.Query` usage, see the :ref:`ormtutorial_toplevel`.
      
      """
      
      _enable_eagerloads = True
      _enable_assertions = True
      _with_labels = False
      _criterion = None
      _yield_per = None
      _lockmode = None
      _order_by = False
      _group_by = False
      _having = None
      _distinct = False
      _offset = None
      _limit = None
      _statement = None
      _correlate = frozenset()
      _populate_existing = False
      _version_check = False
      _autoflush = True
      _current_path = ()
      _only_load_props = None
      _refresh_state = None
      _from_obj = ()
      _filter_aliases = None
      _from_obj_alias = None
      _joinpath = _joinpoint = util.frozendict()
      _execution_options = util.frozendict()
      _params = util.frozendict()
      _attributes = util.frozendict()
      _with_options = ()
      _with_hints = ()
      
      def __init__(self, entities, session=None):
          self.session = session
          self._polymorphic_adapters = {}
          self._set_entities(entities)
  
      def _set_entities(self, entities, entity_wrapper=None):
          if entity_wrapper is None:
              entity_wrapper = _QueryEntity
          self._entities = []
          for ent in util.to_list(entities):
              entity_wrapper(self, ent)
  
          self._setup_aliasizers(self._entities)
  
      def _setup_aliasizers(self, entities):
          if hasattr(self, '_mapper_adapter_map'):
              # usually safe to share a single map, but copying to prevent
              # subtle leaks if end-user is reusing base query with arbitrary
              # number of aliased() objects
              self._mapper_adapter_map = d = self._mapper_adapter_map.copy()
          else:
              self._mapper_adapter_map = d = {}
  
          for ent in entities:
              for entity in ent.entities:
                  if entity not in d:
                      mapper, selectable, is_aliased_class = \
                                              _entity_info(entity)
                      if not is_aliased_class and mapper.with_polymorphic:
                          with_polymorphic = mapper._with_polymorphic_mappers
                          if mapper.mapped_table not in \
                                              self._polymorphic_adapters:
                              self.__mapper_loads_polymorphically_with(mapper, 
                                  sql_util.ColumnAdapter(
                                              selectable, 
                                              mapper._equivalent_columns))
                          adapter = None
                      elif is_aliased_class:
                          adapter = sql_util.ColumnAdapter(
                                              selectable, 
                                              mapper._equivalent_columns)
                          with_polymorphic = None
                      else:
                          with_polymorphic = adapter = None
  
                      d[entity] = (mapper, adapter, selectable, 
                                          is_aliased_class, with_polymorphic)
                  ent.setup_entity(entity, *d[entity])
  
      def __mapper_loads_polymorphically_with(self, mapper, adapter):
          for m2 in mapper._with_polymorphic_mappers:
              self._polymorphic_adapters[m2] = adapter
              for m in m2.iterate_to_root():
                  self._polymorphic_adapters[m.mapped_table] = \
                                  self._polymorphic_adapters[m.local_table] = \
                                  adapter
  
      def _set_select_from(self, *obj):
  
          fa = []
          for from_obj in obj:
              if isinstance(from_obj, expression._SelectBaseMixin):
                  from_obj = from_obj.alias()
              fa.append(from_obj)
  
          self._from_obj = tuple(fa)
  
          if len(self._from_obj) == 1 and \
              isinstance(self._from_obj[0], expression.Alias):
              equivs = self.__all_equivs()
              self._from_obj_alias = sql_util.ColumnAdapter(
                                                  self._from_obj[0], equivs)
          
      def _get_polymorphic_adapter(self, entity, selectable):
          self.__mapper_loads_polymorphically_with(entity.mapper, 
                      sql_util.ColumnAdapter(selectable, 
                              entity.mapper._equivalent_columns))
  
      def _reset_polymorphic_adapter(self, mapper):
          for m2 in mapper._with_polymorphic_mappers:
              self._polymorphic_adapters.pop(m2, None)
              for m in m2.iterate_to_root():
                  self._polymorphic_adapters.pop(m.mapped_table, None)
                  self._polymorphic_adapters.pop(m.local_table, None)
  
      def __adapt_polymorphic_element(self, element):
          if isinstance(element, expression.FromClause):
              search = element
          elif hasattr(element, 'table'):
              search = element.table
          else:
              search = None
  
          if search is not None:
              alias = self._polymorphic_adapters.get(search, None)
              if alias:
                  return alias.adapt_clause(element)
  
      def __replace_element(self, adapters):
          def replace(elem):
              if '_halt_adapt' in elem._annotations:
                  return elem
  
              for adapter in adapters:
                  e = adapter(elem)
                  if e is not None:
                      return e
          return replace
  
      def __replace_orm_element(self, adapters):
          def replace(elem):
              if '_halt_adapt' in elem._annotations:
                  return elem
  
              if "_orm_adapt" in elem._annotations \
                      or "parententity" in elem._annotations:
                  for adapter in adapters:
                      e = adapter(elem)
                      if e is not None:
                          return e
          return replace
  
      @_generative()
      def _adapt_all_clauses(self):
          self._disable_orm_filtering = True
      
      def _adapt_col_list(self, cols):
          return [
                      self._adapt_clause(
                                  expression._literal_as_text(o), 
                                  True, True) 
                      for o in cols
                  ]
          
      def _adapt_clause(self, clause, as_filter, orm_only):
          adapters = []
          if as_filter and self._filter_aliases:
              for fa in self._filter_aliases._visitor_iterator:
                  adapters.append(fa.replace)
  
          if self._from_obj_alias:
              adapters.append(self._from_obj_alias.replace)
  
          if self._polymorphic_adapters:
              adapters.append(self.__adapt_polymorphic_element)
  
          if not adapters:
              return clause
  
          if getattr(self, '_disable_orm_filtering', not orm_only):
              return visitors.replacement_traverse(
                                  clause, 
                                  {'column_collections':False}, 
                                  self.__replace_element(adapters)
                              )
          else:
              return visitors.replacement_traverse(
                                  clause, 
                                  {'column_collections':False}, 
                                  self.__replace_orm_element(adapters)
                              )
  
      def _entity_zero(self):
          return self._entities[0]
  
      def _mapper_zero(self):
          return self._entity_zero().entity_zero
  
      def _extension_zero(self):
          ent = self._entity_zero()
          return getattr(ent, 'extension', ent.mapper.extension)
  
      @property
      def _mapper_entities(self):
          # TODO: this is wrong, its hardcoded to "priamry entity" when
          # for the case of __all_equivs() it should not be
          # the name of this accessor is wrong too
          for ent in self._entities:
              if hasattr(ent, 'primary_entity'):
                  yield ent
  
      def _joinpoint_zero(self):
          return self._joinpoint.get(
                              '_joinpoint_entity',
                              self._entity_zero().entity_zero)
  
      def _mapper_zero_or_none(self):
          if not getattr(self._entities[0], 'primary_entity', False):
              return None
          return self._entities[0].mapper
  
      def _only_mapper_zero(self, rationale=None):
          if len(self._entities) > 1:
              raise sa_exc.InvalidRequestError(
                      rationale or 
                      "This operation requires a Query against a single mapper."
                  )
          return self._mapper_zero()
  
      def _only_entity_zero(self, rationale=None):
          if len(self._entities) > 1:
              raise sa_exc.InvalidRequestError(
                      rationale or 
                      "This operation requires a Query against a single mapper."
                  )
          return self._entity_zero()
  
      def _generate_mapper_zero(self):
          if not getattr(self._entities[0], 'primary_entity', False):
              raise sa_exc.InvalidRequestError(
                              "No primary mapper set up for this Query.")
          entity = self._entities[0]._clone()
          self._entities = [entity] + self._entities[1:]
          return entity
  
      def __all_equivs(self):
          equivs = {}
          for ent in self._mapper_entities:
              equivs.update(ent.mapper._equivalent_columns)
          return equivs
  
      def _get_condition(self):
          self._order_by = self._distinct = False
          return self._no_criterion_condition("get")
          
      def _no_criterion_condition(self, meth):
          if not self._enable_assertions:
              return
          if self._criterion is not None or \
                  self._statement is not None or self._from_obj or \
                  self._limit is not None or self._offset is not None or \
                  self._group_by or self._order_by or self._distinct:
              raise sa_exc.InvalidRequestError(
                                  "Query.%s() being called on a "
                                  "Query with existing criterion. " % meth)
  
          self._from_obj = ()
          self._statement = self._criterion = None
          self._order_by = self._group_by = self._distinct = False
  
      def _no_clauseelement_condition(self, meth):
          if not self._enable_assertions:
              return
          if self._order_by:
              raise sa_exc.InvalidRequestError(
                                  "Query.%s() being called on a "
                                  "Query with existing criterion. " % meth)
          self._no_criterion_condition(meth)
  
      def _no_statement_condition(self, meth):
          if not self._enable_assertions:
              return
          if self._statement:
              raise sa_exc.InvalidRequestError(
                  ("Query.%s() being called on a Query with an existing full "
                   "statement - can't apply criterion.") % meth)
  
      def _no_limit_offset(self, meth):
          if not self._enable_assertions:
              return
          if self._limit is not None or self._offset is not None:
              raise sa_exc.InvalidRequestError(
                  "Query.%s() being called on a Query which already has LIMIT "
                  "or OFFSET applied. To modify the row-limited results of a "
                  " Query, call from_self() first.  "
                  "Otherwise, call %s() before limit() or offset() are applied."
                  % (meth, meth)
              )
  
      def _no_select_modifiers(self, meth):
          if not self._enable_assertions:
              return
          for attr, methname, notset in (
              ('_limit', 'limit()', None),
              ('_offset', 'offset()', None),
              ('_order_by', 'order_by()', False),
              ('_group_by', 'group_by()', False),
              ('_distinct', 'distinct()', False),
          ):
              if getattr(self, attr) is not notset:
                  raise sa_exc.InvalidRequestError(
                      "Can't call Query.%s() when %s has been called" % 
                      (meth, methname)
                  )
  
      def _get_options(self, populate_existing=None, 
                              version_check=None, 
                              only_load_props=None, 
                              refresh_state=None):
          if populate_existing:
              self._populate_existing = populate_existing
          if version_check:
              self._version_check = version_check
          if refresh_state:
              self._refresh_state = refresh_state
          if only_load_props:
              self._only_load_props = set(only_load_props)
          return self
  
      def _clone(self):
          cls = self.__class__
          q = cls.__new__(cls)
          q.__dict__ = self.__dict__.copy()
          return q
  
      @property
      def statement(self):
          """The full SELECT statement represented by this Query.
          
          The statement by default will not have disambiguating labels
          applied to the construct unless with_labels(True) is called
          first.
          
          """
  
          stmt = self._compile_context(labels=self._with_labels).\
                          statement
          if self._params:
              stmt = stmt.params(self._params)
          return stmt._annotate({'_halt_adapt': True})
  
      def subquery(self):
          """return the full SELECT statement represented by this Query, 
          embedded within an Alias.
  
          Eager JOIN generation within the query is disabled.
  
          The statement by default will not have disambiguating labels
          applied to the construct unless with_labels(True) is called
          first.
  
          """
          return self.enable_eagerloads(False).statement.alias()
  
      def __clause_element__(self):
          return self.enable_eagerloads(False).with_labels().statement
  
      @_generative()
      def enable_eagerloads(self, value):
          """Control whether or not eager joins and subqueries are 
          rendered.
  
          When set to False, the returned Query will not render
          eager joins regardless of :func:`~sqlalchemy.orm.joinedload`,
          :func:`~sqlalchemy.orm.subqueryload` options
          or mapper-level ``lazy='joined'``/``lazy='subquery'``
          configurations.
  
          This is used primarily when nesting the Query's
          statement into a subquery or other
          selectable.
  
          """
          self._enable_eagerloads = value
  
      @_generative()
      def with_labels(self):
          """Apply column labels to the return value of Query.statement.
  
          Indicates that this Query's `statement` accessor should return
          a SELECT statement that applies labels to all columns in the
          form <tablename>_<columnname>; this is commonly used to
          disambiguate columns from multiple tables which have the same
          name.
  
          When the `Query` actually issues SQL to load rows, it always
          uses column labeling.
  
          """
          self._with_labels = True
      
      @_generative()
      def enable_assertions(self, value):
          """Control whether assertions are generated.
          
          When set to False, the returned Query will 
          not assert its state before certain operations, 
          including that LIMIT/OFFSET has not been applied
          when filter() is called, no criterion exists
          when get() is called, and no "from_statement()"
          exists when filter()/order_by()/group_by() etc.
          is called.  This more permissive mode is used by 
          custom Query subclasses to specify criterion or 
          other modifiers outside of the usual usage patterns.
          
          Care should be taken to ensure that the usage 
          pattern is even possible.  A statement applied
          by from_statement() will override any criterion
          set by filter() or order_by(), for example.
          
          """
          self._enable_assertions = value
          
      @property
      def whereclause(self):
          """The WHERE criterion for this Query."""
          return self._criterion
  
      @_generative()
      def _with_current_path(self, path):
          """indicate that this query applies to objects loaded 
          within a certain path.
  
          Used by deferred loaders (see strategies.py) which transfer 
          query options from an originating query to a newly generated 
          query intended for the deferred load.
  
          """
          self._current_path = path
  
      @_generative(_no_clauseelement_condition)
      def with_polymorphic(self, 
                                      cls_or_mappers, 
                                      selectable=None, discriminator=None):
          """Load columns for descendant mappers of this Query's mapper.
  
          Using this method will ensure that each descendant mapper's
          tables are included in the FROM clause, and will allow filter()
          criterion to be used against those tables.  The resulting
          instances will also have those columns already loaded so that
          no "post fetch" of those columns will be required.
  
          :param cls_or_mappers: a single class or mapper, or list of
              class/mappers, which inherit from this Query's mapper.
              Alternatively, it may also be the string ``'*'``, in which case
              all descending mappers will be added to the FROM clause.
  
          :param selectable: a table or select() statement that will
              be used in place of the generated FROM clause. This argument is
              required if any of the desired mappers use concrete table
              inheritance, since SQLAlchemy currently cannot generate UNIONs
              among tables automatically. If used, the ``selectable`` argument
              must represent the full set of tables and columns mapped by every
              desired mapper. Otherwise, the unaccounted mapped columns will
              result in their table being appended directly to the FROM clause
              which will usually lead to incorrect results.
  
          :param discriminator: a column to be used as the "discriminator"
              column for the given selectable. If not given, the polymorphic_on
              attribute of the mapper will be used, if any. This is useful for
              mappers that don't have polymorphic loading behavior by default,
              such as concrete table mappers.
  
          """
          entity = self._generate_mapper_zero()
          entity.set_with_polymorphic(self, 
                                          cls_or_mappers, 
                                          selectable=selectable,
                                          discriminator=discriminator)
  
      @_generative()
      def yield_per(self, count):
          """Yield only ``count`` rows at a time.
  
          WARNING: use this method with caution; if the same instance is present
          in more than one batch of rows, end-user changes to attributes will be
          overwritten.
  
          In particular, it's usually impossible to use this setting with
          eagerly loaded collections (i.e. any lazy='joined' or 'subquery') 
          since those collections will be cleared for a new load when 
          encountered in a subsequent result batch.   In the case of 'subquery'
          loading, the full result for all rows is fetched which generally
          defeats the purpose of :meth:`~sqlalchemy.orm.query.Query.yield_per`.
  
          Also note that many DBAPIs do not "stream" results, pre-buffering
          all rows before making them available, including mysql-python and 
          psycopg2.  :meth:`~sqlalchemy.orm.query.Query.yield_per` will also 
          set the ``stream_results`` execution
          option to ``True``, which currently is only understood by psycopg2
          and causes server side cursors to be used.
          
          """
          self._yield_per = count
          self._execution_options = self._execution_options.copy()
          self._execution_options['stream_results'] = True
          
      def get(self, ident):
          """Return an instance of the object based on the 
          given identifier, or None if not found.
  
          The `ident` argument is a scalar or tuple of primary key column values
          in the order of the table def's primary key columns.
  
          """
  
          # convert composite types to individual args
          if hasattr(ident, '__composite_values__'):
              ident = ident.__composite_values__()
  
          key = self._only_mapper_zero(
                      "get() can only be used against a single mapped class."
                  ).identity_key_from_primary_key(ident)
          return self._get(key, ident)
  
      @_generative()
      def correlate(self, *args):
          """Return a :class:`.Query` construct which will correlate the given
          FROM clauses to that of an enclosing :class:`.Query` or
          :func:`~.expression.select`.
          
          The method here accepts mapped classes, :func:`.aliased` constructs,
          and :func:`.mapper` constructs as arguments, which are resolved into
          expression constructs, in addition to appropriate expression
          constructs.
          
          The correlation arguments are ultimately passed to
          :meth:`.Select.correlate` after coercion to expression constructs.
          
          The correlation arguments take effect in such cases
          as when :meth:`.Query.from_self` is used, or when 
          a subquery as returned by :meth:`.Query.subquery` is 
          embedded in another :func:`~.expression.select` construct.
          
           """
          
          self._correlate = self._correlate.union(
                                          _orm_selectable(s) 
                                          for s in args)
  
      @_generative()
      def autoflush(self, setting):
          """Return a Query with a specific 'autoflush' setting.
  
          Note that a Session with autoflush=False will
          not autoflush, even if this flag is set to True at the
          Query level.  Therefore this flag is usually used only
          to disable autoflush for a specific Query.
  
          """
          self._autoflush = setting
  
      @_generative()
      def populate_existing(self):
          """Return a Query that will refresh all instances loaded.
  
          This includes all entities accessed from the database, including
          secondary entities, eagerly-loaded collection items.
  
          All changes present on entities which are already present in the
          session will be reset and the entities will all be marked "clean".
  
          An alternative to populate_existing() is to expire the Session
          fully using session.expire_all().
  
          """
          self._populate_existing = True
  
      def with_parent(self, instance, property=None):
          """Add filtering criterion that relates the given instance
          to a child object or collection, using its attribute state 
          as well as an established :func:`.relationship()`
          configuration.
          
          The method uses the :func:`.with_parent` function to generate
          the clause, the result of which is passed to :meth:`.Query.filter`.
          
          Parameters are the same as :func:`.with_parent`, with the exception
          that the given property can be None, in which case a search is
          performed against this :class:`.Query` object's target mapper.
          
          """
          
          if property is None:
              from sqlalchemy.orm import properties
              mapper = object_mapper(instance)
  
              for prop in mapper.iterate_properties:
                  if isinstance(prop, properties.PropertyLoader) and \
                      prop.mapper is self._mapper_zero():
                      property = prop
                      break
              else:
                  raise sa_exc.InvalidRequestError(
                          "Could not locate a property which relates instances "
                          "of class '%s' to instances of class '%s'" % 
                          (
                              self._mapper_zero().class_.__name__,
                              instance.__class__.__name__)
                          )
  
          return self.filter(with_parent(instance, property))
  
      @_generative()
      def add_entity(self, entity, alias=None):
          """add a mapped entity to the list of result columns 
          to be returned."""
  
          if alias is not None:
              entity = aliased(entity, alias)
  
          self._entities = list(self._entities)
          m = _MapperEntity(self, entity)
          self._setup_aliasizers([m])
  
      def from_self(self, *entities):
          """return a Query that selects from this Query's 
          SELECT statement.
  
          \*entities - optional list of entities which will replace
          those being selected.
  
          """
          fromclause = self.with_labels().enable_eagerloads(False).\
                                      statement.correlate(None)
          q = self._from_selectable(fromclause)
          if entities:
              q._set_entities(entities)
          return q
      
      @_generative()
      def _from_selectable(self, fromclause):
          for attr in ('_statement', '_criterion', '_order_by', '_group_by',
                  '_limit', '_offset', '_joinpath', '_joinpoint', 
                  '_distinct'
          ):
              self.__dict__.pop(attr, None)
          self._set_select_from(fromclause)
          old_entities = self._entities
          self._entities = []
          for e in old_entities:
              e.adapt_to_selectable(self, self._from_obj[0])
  
      def values(self, *columns):
          """Return an iterator yielding result tuples corresponding 
          to the given list of columns"""
  
          if not columns:
              return iter(())
          q = self._clone()
          q._set_entities(columns, entity_wrapper=_ColumnEntity)
          if not q._yield_per:
              q._yield_per = 10
          return iter(q)
      _values = values
  
      def value(self, column):
          """Return a scalar result corresponding to the given 
          column expression."""
          try:
              # Py3K
              #return self.values(column).__next__()[0]
              # Py2K
              return self.values(column).next()[0]
              # end Py2K
          except StopIteration:
              return None
  
      @_generative()
      def add_columns(self, *column):
          """Add one or more column expressions to the list 
          of result columns to be returned."""
  
          self._entities = list(self._entities)
          l = len(self._entities)
          for c in column:
              _ColumnEntity(self, c)
          # _ColumnEntity may add many entities if the
          # given arg is a FROM clause
          self._setup_aliasizers(self._entities[l:])
  
      @util.pending_deprecation("0.7", 
                  ":meth:`.add_column` is superceded by :meth:`.add_columns`", 
                  False)
      def add_column(self, column):
          """Add a column expression to the list of result columns to be returned.
          
          Pending deprecation: :meth:`.add_column` will be superceded by 
          :meth:`.add_columns`.
          
          """
          
          return self.add_columns(column)
  
      def options(self, *args):
          """Return a new Query object, applying the given list of
          mapper options.
          
          Most supplied options regard changing how column- and
          relationship-mapped attributes are loaded. See the sections
          :ref:`deferred` and :ref:`loading_toplevel` for reference
          documentation.
          
          """
          return self._options(False, *args)
  
      def _conditional_options(self, *args):
          return self._options(True, *args)
  
      @_generative()
      def _options(self, conditional, *args):
          # most MapperOptions write to the '_attributes' dictionary,
          # so copy that as well
          self._attributes = self._attributes.copy()
          opts = tuple(util.flatten_iterator(args))
          self._with_options = self._with_options + opts
          if conditional:
              for opt in opts:
                  opt.process_query_conditionally(self)
          else:
              for opt in opts:
                  opt.process_query(self)
  
      @_generative()
      def with_hint(self, selectable, text, dialect_name=None):
          """Add an indexing hint for the given entity or selectable to 
          this :class:`Query`.
          
          Functionality is passed straight through to 
          :meth:`~sqlalchemy.sql.expression.Select.with_hint`, 
          with the addition that ``selectable`` can be a 
          :class:`Table`, :class:`Alias`, or ORM entity / mapped class 
          /etc.
          """
          mapper, selectable, is_aliased_class = _entity_info(selectable)
          
          self._with_hints += ((selectable, text, dialect_name),)
          
      @_generative()
      def execution_options(self, **kwargs):
          """ Set non-SQL options which take effect during execution.
          
          The options are the same as those accepted by 
          :meth:`sqlalchemy.sql.expression.Executable.execution_options`.
          
          Note that the ``stream_results`` execution option is enabled
          automatically if the :meth:`~sqlalchemy.orm.query.Query.yield_per()`
          method is used.
  
          """
          self._execution_options = self._execution_options.union(kwargs)
  
      @_generative()
      def with_lockmode(self, mode):
          """Return a new Query object with the specified locking mode."""
  
          self._lockmode = mode
  
      @_generative()
      def params(self, *args, **kwargs):
          """add values for bind parameters which may have been 
          specified in filter().
  
          parameters may be specified using \**kwargs, or optionally a single
          dictionary as the first positional argument. The reason for both is
          that \**kwargs is convenient, however some parameter dictionaries
          contain unicode keys in which case \**kwargs cannot be used.
  
          """
          if len(args) == 1:
              kwargs.update(args[0])
          elif len(args) > 0:
              raise sa_exc.ArgumentError(
                              "params() takes zero or one positional argument, "
                              "which is a dictionary.")
          self._params = self._params.copy()
          self._params.update(kwargs)
  
      @_generative(_no_statement_condition, _no_limit_offset)
      def filter(self, criterion):
          """apply the given filtering criterion to the query and return 
          the newly resulting ``Query``
  
          the criterion is any sql.ClauseElement applicable to the WHERE clause
          of a select.
  
          """
          if isinstance(criterion, basestring):
              criterion = sql.text(criterion)
  
          if criterion is not None and \
                  not isinstance(criterion, sql.ClauseElement):
              raise sa_exc.ArgumentError(
                          "filter() argument must be of type "
                          "sqlalchemy.sql.ClauseElement or string")
  
          criterion = self._adapt_clause(criterion, True, True)
  
          if self._criterion is not None:
              self._criterion = self._criterion & criterion
          else:
              self._criterion = criterion
  
      def filter_by(self, **kwargs):
          """apply the given filtering criterion to the query and return 
          the newly resulting ``Query``."""
  
          clauses = [_entity_descriptor(self._joinpoint_zero(), key) == value
              for key, value in kwargs.iteritems()]
  
          return self.filter(sql.and_(*clauses))
  
      @_generative(_no_statement_condition, _no_limit_offset)
      @util.accepts_a_list_as_starargs(list_deprecation='deprecated')
      def order_by(self, *criterion):
          """apply one or more ORDER BY criterion to the query and return 
          the newly resulting ``Query``
          
          All existing ORDER BY settings can be suppressed by 
          passing ``None`` - this will suppress any ORDER BY configured
          on mappers as well.
          
          Alternatively, an existing ORDER BY setting on the Query
          object can be entirely cancelled by passing ``False`` 
          as the value - use this before calling methods where
          an ORDER BY is invalid.
          
          """
  
          if len(criterion) == 1:
              if criterion[0] is False:
                  if '_order_by' in self.__dict__:
                      del self._order_by
                  return
              if criterion[0] is None:
                  self._order_by = None
                  return
                  
          criterion = self._adapt_col_list(criterion)
  
          if self._order_by is False or self._order_by is None:
              self._order_by = criterion
          else:
              self._order_by = self._order_by + criterion
  
      @_generative(_no_statement_condition, _no_limit_offset)
      @util.accepts_a_list_as_starargs(list_deprecation='deprecated')
      def group_by(self, *criterion):
          """apply one or more GROUP BY criterion to the query and return 
          the newly resulting ``Query``"""
  
          criterion = list(chain(*[_orm_columns(c) for c in criterion]))
  
          criterion = self._adapt_col_list(criterion)
  
          if self._group_by is False:
              self._group_by = criterion
          else:
              self._group_by = self._group_by + criterion
  
      @_generative(_no_statement_condition, _no_limit_offset)
      def having(self, criterion):
          """apply a HAVING criterion to the query and return the 
          newly resulting ``Query``."""
  
          if isinstance(criterion, basestring):
              criterion = sql.text(criterion)
  
          if criterion is not None and \
                  not isinstance(criterion, sql.ClauseElement):
              raise sa_exc.ArgumentError(
                      "having() argument must be of type "
                      "sqlalchemy.sql.ClauseElement or string")
  
          criterion = self._adapt_clause(criterion, True, True)
  
          if self._having is not None:
              self._having = self._having & criterion
          else:
              self._having = criterion
  
      def union(self, *q):
          """Produce a UNION of this Query against one or more queries.
  
          e.g.::
  
              q1 = sess.query(SomeClass).filter(SomeClass.foo=='bar')
              q2 = sess.query(SomeClass).filter(SomeClass.bar=='foo')
  
              q3 = q1.union(q2)
  
          The method accepts multiple Query objects so as to control
          the level of nesting.  A series of ``union()`` calls such as::
  
              x.union(y).union(z).all()
  
          will nest on each ``union()``, and produces::
  
              SELECT * FROM (SELECT * FROM (SELECT * FROM X UNION 
                              SELECT * FROM y) UNION SELECT * FROM Z)
  
          Whereas::
  
              x.union(y, z).all()
  
          produces::
  
              SELECT * FROM (SELECT * FROM X UNION SELECT * FROM y UNION 
                              SELECT * FROM Z)
  
          """
          
          
          return self._from_selectable(
                      expression.union(*([self]+ list(q))))
  
      def union_all(self, *q):
          """Produce a UNION ALL of this Query against one or more queries.
  
          Works the same way as :meth:`~sqlalchemy.orm.query.Query.union`. See
          that method for usage examples.
  
          """
          return self._from_selectable(
                      expression.union_all(*([self]+ list(q)))
                  )
  
      def intersect(self, *q):
          """Produce an INTERSECT of this Query against one or more queries.
  
          Works the same way as :meth:`~sqlalchemy.orm.query.Query.union`. See
          that method for usage examples.
  
          """
          return self._from_selectable(
                      expression.intersect(*([self]+ list(q)))
                  )
  
      def intersect_all(self, *q):
          """Produce an INTERSECT ALL of this Query against one or more queries.
  
          Works the same way as :meth:`~sqlalchemy.orm.query.Query.union`. See
          that method for usage examples.
  
          """
          return self._from_selectable(
                      expression.intersect_all(*([self]+ list(q)))
                  )
  
      def except_(self, *q):
          """Produce an EXCEPT of this Query against one or more queries.
  
          Works the same way as :meth:`~sqlalchemy.orm.query.Query.union`. See
          that method for usage examples.
  
          """
          return self._from_selectable(
                      expression.except_(*([self]+ list(q)))
                  )
  
      def except_all(self, *q):
          """Produce an EXCEPT ALL of this Query against one or more queries.
  
          Works the same way as :meth:`~sqlalchemy.orm.query.Query.union`. See
          that method for usage examples.
  
          """
          return self._from_selectable(
                      expression.except_all(*([self]+ list(q)))
                  )
  
      @util.accepts_a_list_as_starargs(list_deprecation='deprecated')
      def join(self, *props, **kwargs):
          """Create a join against this ``Query`` object's criterion
          and apply generatively, returning the newly resulting ``Query``.
  
          Each element in \*props may be:
  
            * a string property name, i.e. "rooms".  This will join along the
              relationship of the same name from this Query's "primary" mapper,
              if one is present.
  
            * a class-mapped attribute, i.e. Houses.rooms.  This will create a
              join from "Houses" table to that of the "rooms" relationship.
  
            * a 2-tuple containing a target class or selectable, and an "ON"
              clause.  The ON clause can be the property name/ attribute like
              above, or a SQL expression.
  
          e.g.::
  
              # join along string attribute names
              session.query(Company).join('employees')
              session.query(Company).join('employees', 'tasks')
  
              # join the Person entity to an alias of itself,
              # along the "friends" relationship
              PAlias = aliased(Person)
              session.query(Person).join((Palias, Person.friends))
  
              # join from Houses to the "rooms" attribute on the
              # "Colonials" subclass of Houses, then join to the
              # "closets" relationship on Room
              session.query(Houses).join(Colonials.rooms, Room.closets)
  
              # join from Company entities to the "employees" collection,
              # using "people JOIN engineers" as the target.  Then join
              # to the "computers" collection on the Engineer entity.
              session.query(Company).\
                          join((people.join(engineers), 'employees'),
                          Engineer.computers)
  
              # join from Articles to Keywords, using the "keywords" attribute.
              # assume this is a many-to-many relationship.
              session.query(Article).join(Article.keywords)
  
              # same thing, but spelled out entirely explicitly
              # including the association table.
              session.query(Article).join(
                  (article_keywords,
                  Articles.id==article_keywords.c.article_id),
                  (Keyword, Keyword.id==article_keywords.c.keyword_id)
                  )
  
          \**kwargs include:
  
              aliased - when joining, create anonymous aliases of each table.
              This is used for self-referential joins or multiple joins to the
              same table. Consider usage of the aliased(SomeClass) construct as
              a more explicit approach to this.
  
              from_joinpoint - when joins are specified using string property
              names, locate the property from the mapper found in the most
              recent previous join() call, instead of from the root entity.
  
          """
          aliased, from_joinpoint = kwargs.pop('aliased', False),\
                                      kwargs.pop('from_joinpoint', False)
          if kwargs:
              raise TypeError("unknown arguments: %s" %
                                  ','.join(kwargs.iterkeys()))
          return self._join(props, 
                              outerjoin=False, create_aliases=aliased, 
                              from_joinpoint=from_joinpoint)
  
      @util.accepts_a_list_as_starargs(list_deprecation='deprecated')
      def outerjoin(self, *props, **kwargs):
          """Create a left outer join against this ``Query`` object's criterion
          and apply generatively, retunring the newly resulting ``Query``.
  
          Usage is the same as the ``join()`` method.
  
          """
          aliased, from_joinpoint = kwargs.pop('aliased', False), \
                                  kwargs.pop('from_joinpoint', False)
          if kwargs:
              raise TypeError("unknown arguments: %s" %
                      ','.join(kwargs.iterkeys()))
          return self._join(props, 
                              outerjoin=True, create_aliases=aliased, 
                              from_joinpoint=from_joinpoint)
  
      @_generative(_no_statement_condition, _no_limit_offset)
      def _join(self, keys, outerjoin, create_aliases, from_joinpoint):
          """consumes arguments from join() or outerjoin(), places them into a
          consistent format with which to form the actual JOIN constructs.
          
          """
          self._polymorphic_adapters = self._polymorphic_adapters.copy()
  
          if not from_joinpoint:
              self._reset_joinpoint()
          
          if len(keys) >= 2 and \
                  isinstance(keys[1], expression.ClauseElement) and \
                  not isinstance(keys[1], expression.FromClause):
              raise sa_exc.ArgumentError(
                  "You appear to be passing a clause expression as the second "
                  "argument to query.join().   Did you mean to use the form "
                  "query.join((target, onclause))?  Note the tuple.")
              
          for arg1 in util.to_list(keys):
              if isinstance(arg1, tuple):
                  arg1, arg2 = arg1
              else:
                  arg2 = None
  
              # determine onclause/right_entity.  there
              # is a little bit of legacy behavior still at work here
              # which means they might be in either order.  may possibly
              # lock this down to (right_entity, onclause) in 0.6.
              if isinstance(arg1, (interfaces.PropComparator, basestring)):
                  right_entity, onclause = arg2, arg1
              else:
                  right_entity, onclause = arg1, arg2
  
              left_entity = prop = None
              
              if isinstance(onclause, basestring):
                  left_entity = self._joinpoint_zero()
  
                  descriptor = _entity_descriptor(left_entity, onclause)
                  onclause = descriptor
              
              # check for q.join(Class.propname, from_joinpoint=True)
              # and Class is that of the current joinpoint
              elif from_joinpoint and \
                          isinstance(onclause, interfaces.PropComparator):
                  left_entity = onclause.parententity
                  
                  left_mapper, left_selectable, left_is_aliased = \
                                      _entity_info(self._joinpoint_zero())
                  if left_mapper is left_entity:
                      left_entity = self._joinpoint_zero()
                      descriptor = _entity_descriptor(left_entity,
                                                              onclause.key)
                      onclause = descriptor
  
              if isinstance(onclause, interfaces.PropComparator):
                  if right_entity is None:
                      right_entity = onclause.property.mapper
                      of_type = getattr(onclause, '_of_type', None)
                      if of_type:
                          right_entity = of_type
                      else:
                          right_entity = onclause.property.mapper
              
                  left_entity = onclause.parententity
                  
                  prop = onclause.property
                  if not isinstance(onclause,  attributes.QueryableAttribute):
                      onclause = prop
  
                  if not create_aliases:
                      # check for this path already present.
                      # don't render in that case.
                      if (left_entity, right_entity, prop.key) in \
                                      self._joinpoint:
                          self._joinpoint = \
                                      self._joinpoint[
                                      (left_entity, right_entity, prop.key)]
                          continue
  
              elif onclause is not None and right_entity is None:
                  # TODO: no coverage here
                  raise NotImplementedError("query.join(a==b) not supported.")
              
              self._join_left_to_right(
                                  left_entity, 
                                  right_entity, onclause, 
                                  outerjoin, create_aliases, prop)
  
      def _join_left_to_right(self, left, right, 
                              onclause, outerjoin, create_aliases, prop):
          """append a JOIN to the query's from clause."""
          
          if left is None:
              left = self._joinpoint_zero()
  
          if left is right and \
                  not create_aliases:
              raise sa_exc.InvalidRequestError(
                          "Can't construct a join from %s to %s, they "
                          "are the same entity" % 
                          (left, right))
              
          left_mapper, left_selectable, left_is_aliased = _entity_info(left)
          right_mapper, right_selectable, is_aliased_class = _entity_info(right)
  
          if right_mapper and prop and \
                  not right_mapper.common_parent(prop.mapper):
              raise sa_exc.InvalidRequestError(
                      "Join target %s does not correspond to "
                      "the right side of join condition %s" % (right, onclause)
              )
  
          if not right_mapper and prop:
              right_mapper = prop.mapper
  
          need_adapter = False
  
          if right_mapper and right is right_selectable:
              if not right_selectable.is_derived_from(
                                      right_mapper.mapped_table):
                  raise sa_exc.InvalidRequestError(
                      "Selectable '%s' is not derived from '%s'" %
                      (right_selectable.description,
                      right_mapper.mapped_table.description))
  
              if not isinstance(right_selectable, expression.Alias):
                  right_selectable = right_selectable.alias()
  
              right = aliased(right_mapper, right_selectable)
              need_adapter = True
  
          aliased_entity = right_mapper and \
                              not is_aliased_class and \
                              (
                                  right_mapper.with_polymorphic or
                                  isinstance(
                                      right_mapper.mapped_table,
                                      expression.Join)
                              )
  
          if not need_adapter and (create_aliases or aliased_entity):
              right = aliased(right)
              need_adapter = True
  
          # if joining on a MapperProperty path,
          # track the path to prevent redundant joins
          if not create_aliases and prop:
  
              self._joinpoint = jp = {
                  '_joinpoint_entity':right,
                  'prev':((left, right, prop.key), self._joinpoint)
              }
  
              # copy backwards to the root of the _joinpath
              # dict, so that no existing dict in the path is mutated
              while 'prev' in jp:
                  f, prev = jp['prev']
                  prev = prev.copy()
                  prev[f] = jp
                  jp['prev'] = (f, prev)
                  jp = prev
  
              self._joinpath = jp
  
          else:
              self._joinpoint = {
                  '_joinpoint_entity':right
              }
          
          # if an alias() of the right side was generated here,
          # apply an adapter to all subsequent filter() calls
          # until reset_joinpoint() is called.
          if need_adapter:
              self._filter_aliases = ORMAdapter(right,
                          equivalents=right_mapper._equivalent_columns,
                          chain_to=self._filter_aliases)
  
          # if the onclause is a ClauseElement, adapt it with any 
          # adapters that are in place right now
          if isinstance(onclause, expression.ClauseElement):
              onclause = self._adapt_clause(onclause, True, True)
          
          # if an alias() on the right side was generated,
          # which is intended to wrap a the right side in a subquery,
          # ensure that columns retrieved from this target in the result
          # set are also adapted.
          if aliased_entity:
              self.__mapper_loads_polymorphically_with(
                          right_mapper,
                          ORMAdapter(
                              right, 
                              equivalents=right_mapper._equivalent_columns
                          )
                      )
          
          join_to_left = not is_aliased_class and not left_is_aliased
  
          if self._from_obj and left_selectable is not None:
              replace_clause_index, clause = sql_util.find_join_source(
                                                      self._from_obj, 
                                                      left_selectable)
              if clause is not None:
                  # the entire query's FROM clause is an alias of itself (i.e.
                  # from_self(), similar). if the left clause is that one,
                  # ensure it aliases to the left side.
                  if self._from_obj_alias and clause is self._from_obj[0]:
                      join_to_left = True
  
                  clause = orm_join(clause, 
                                      right, 
                                      onclause, isouter=outerjoin, 
                                      join_to_left=join_to_left)
  
                  self._from_obj = \
                          self._from_obj[:replace_clause_index] + \
                          (clause, ) + \
                          self._from_obj[replace_clause_index + 1:]
                  return
  
          if left_mapper:
              for ent in self._entities:
                  if ent.corresponds_to(left):
                      clause = ent.selectable
                      break
              else:
                  clause = left
          else:
              clause = None
  
          if clause is None:
              raise sa_exc.InvalidRequestError(
                      "Could not find a FROM clause to join from")
  
          clause = orm_join(clause, right, onclause, 
                                  isouter=outerjoin, join_to_left=join_to_left)
              
          self._from_obj = self._from_obj + (clause,)
  
      def _reset_joinpoint(self):
          self._joinpoint = self._joinpath
          self._filter_aliases = None
  
      @_generative(_no_statement_condition)
      def reset_joinpoint(self):
          """return a new Query reset the 'joinpoint' of this Query reset
          back to the starting mapper.  Subsequent generative calls will
          be constructed from the new joinpoint.
  
          Note that each call to join() or outerjoin() also starts from
          the root.
  
          """
          self._reset_joinpoint()
  
      @_generative(_no_clauseelement_condition)
      def select_from(self, *from_obj):
          """Set the `from_obj` parameter of the query and return the newly
          resulting ``Query``.  This replaces the table which this Query selects
          from with the given table.
          
          ``select_from()`` also accepts class arguments. Though usually not
          necessary, can ensure that the full selectable of the given mapper is
          applied, e.g. for joined-table mappers.
  
          """
          
          obj = []
          for fo in from_obj:
              if _is_mapped_class(fo):
                  mapper, selectable, is_aliased_class = _entity_info(fo)
                  obj.append(selectable)
              elif not isinstance(fo, expression.FromClause):
                  raise sa_exc.ArgumentError(
                              "select_from() accepts FromClause objects only.")
              else:
                  obj.append(fo)  
                  
          self._set_select_from(*obj)
  
      def __getitem__(self, item):
          if isinstance(item, slice):
              start, stop, step = util.decode_slice(item)
  
              if isinstance(stop, int) and \
                  isinstance(start, int) and \
                  stop - start <= 0:
                  return []
  
              # perhaps we should execute a count() here so that we
              # can still use LIMIT/OFFSET ?
              elif (isinstance(start, int) and start < 0) \
                  or (isinstance(stop, int) and stop < 0):
                  return list(self)[item]
  
              res = self.slice(start, stop)
              if step is not None:
                  return list(res)[None:None:item.step]
              else:
                  return list(res)
          else:
              return list(self[item:item+1])[0]
  
      @_generative(_no_statement_condition)
      def slice(self, start, stop):
          """apply LIMIT/OFFSET to the ``Query`` based on a "
          "range and return the newly resulting ``Query``."""
          
          if start is not None and stop is not None:
              self._offset = (self._offset or 0) + start
              self._limit = stop - start
          elif start is None and stop is not None:
              self._limit = stop
          elif start is not None and stop is None:
              self._offset = (self._offset or 0) + start
  
      @_generative(_no_statement_condition)
      def limit(self, limit):
          """Apply a ``LIMIT`` to the query and return the newly resulting
  
          ``Query``.
  
          """
          self._limit = limit
  
      @_generative(_no_statement_condition)
      def offset(self, offset):
          """Apply an ``OFFSET`` to the query and return the newly resulting
          ``Query``.
  
          """
          self._offset = offset
  
      @_generative(_no_statement_condition)
      def distinct(self):
          """Apply a ``DISTINCT`` to the query and return the newly resulting
          ``Query``.
  
          """
          self._distinct = True
  
      def all(self):
          """Return the results represented by this ``Query`` as a list.
  
          This results in an execution of the underlying query.
  
          """
          return list(self)
  
      @_generative(_no_clauseelement_condition)
      def from_statement(self, statement):
          """Execute the given SELECT statement and return results.
  
          This method bypasses all internal statement compilation, and the
          statement is executed without modification.
  
          The statement argument is either a string, a ``select()`` construct,
          or a ``text()`` construct, and should return the set of columns
          appropriate to the entity class represented by this ``Query``.
  
          Also see the ``instances()`` method.
  
          """
          if isinstance(statement, basestring):
              statement = sql.text(statement)
  
          if not isinstance(statement, 
                              (expression._TextClause,
                              expression._SelectBaseMixin)):
              raise sa_exc.ArgumentError(
                              "from_statement accepts text(), select(), "
                              "and union() objects only.")
  
          self._statement = statement
  
      def first(self):
          """Return the first result of this ``Query`` or 
          None if the result doesn't contain any row.
             
          first() applies a limit of one within the generated SQL, so that
          only one primary entity row is generated on the server side 
          (note this may consist of multiple result rows if join-loaded 
          collections are present).
  
          Calling ``first()`` results in an execution of the underlying query.
  
          """
          if self._statement is not None:
              ret = list(self)[0:1]
          else:
              ret = list(self[0:1])
          if len(ret) > 0:
              return ret[0]
          else:
              return None
  
      def one(self):
          """Return exactly one result or raise an exception.
  
          Raises ``sqlalchemy.orm.exc.NoResultFound`` if the query selects 
          no rows.  Raises ``sqlalchemy.orm.exc.MultipleResultsFound`` 
          if multiple object identities are returned, or if multiple
          rows are returned for a query that does not return object
          identities.
          
          Note that an entity query, that is, one which selects one or
          more mapped classes as opposed to individual column attributes,
          may ultimately represent many rows but only one row of 
          unique entity or entities - this is a successful result for one().
  
          Calling ``one()`` results in an execution of the underlying query.
          As of 0.6, ``one()`` fully fetches all results instead of applying 
          any kind of limit, so that the "unique"-ing of entities does not 
          conceal multiple object identities.
  
          """
          ret = list(self)
          
          l = len(ret)
          if l == 1:
              return ret[0]
          elif l == 0:
              raise orm_exc.NoResultFound("No row was found for one()")
          else:
              raise orm_exc.MultipleResultsFound(
                  "Multiple rows were found for one()")
  
      def scalar(self):
          """Return the first element of the first result or None
          if no rows present.  If multiple rows are returned,
          raises MultipleResultsFound.
  
            >>> session.query(Item).scalar()
            <Item>
            >>> session.query(Item.id).scalar()
            1
            >>> session.query(Item.id).filter(Item.id < 0).scalar()
            None
            >>> session.query(Item.id, Item.name).scalar()
            1
            >>> session.query(func.count(Parent.id)).scalar()
            20
  
          This results in an execution of the underlying query.
  
          """
          try:
              ret = self.one()
              if not isinstance(ret, tuple):
                  return ret
              return ret[0]
          except orm_exc.NoResultFound:
              return None
  
      def __iter__(self):
          context = self._compile_context()
          context.statement.use_labels = True
          if self._autoflush and not self._populate_existing:
              self.session._autoflush()
          return self._execute_and_instances(context)
  
      def _execute_and_instances(self, querycontext):
          result = self.session.execute(
                          querycontext.statement, params=self._params,
                          mapper=self._mapper_zero_or_none())
          return self.instances(result, querycontext)
      
      @property
      def column_descriptions(self):
          """Return metadata about the columns which would be 
          returned by this :class:`Query`.
          
          Format is a list of dictionaries::
              
              user_alias = aliased(User, name='user2')
              q = sess.query(User, User.id, user_alias)
              
              # this expression:
              q.columns
              
              # would return:
              [
                  {
                      'name':'User',
                      'type':User,
                      'aliased':False,
                      'expr':User,
                  },
                  {
                      'name':'id',
                      'type':Integer(),
                      'aliased':False,
                      'expr':User.id,
                  },
                  {
                      'name':'user2',
                      'type':User,
                      'aliased':True,
                      'expr':user_alias
                  }
              ]
              
          """
          return [
              {
                  'name':ent._label_name,
                  'type':ent.type,
                  'aliased':getattr(ent, 'is_aliased_class', False),
                  'expr':ent.expr
              }
              for ent in self._entities
          ]
          
      def instances(self, cursor, __context=None):
          """Given a ResultProxy cursor as returned by connection.execute(),
          return an ORM result as an iterator.
  
          e.g.::
  
              result = engine.execute("select * from users")
              for u in session.query(User).instances(result):
                  print u
          """
          session = self.session
  
          context = __context
          if context is None:
              context = QueryContext(self)
  
          context.runid = _new_runid()
  
          filtered = bool(list(self._mapper_entities))
          single_entity = filtered and len(self._entities) == 1
  
          if filtered:
              if single_entity:
                  filter = lambda x: util.unique_list(x, util.IdentitySet)
              else:
                  filter = util.unique_list
          else:
              filter = None
  
          custom_rows = single_entity and \
                          'append_result' in self._entities[0].extension
  
          (process, labels) = \
                      zip(*[
                          query_entity.row_processor(self, context, custom_rows)
                          for query_entity in self._entities
                      ])
  
          if not single_entity:
              labels = [l for l in labels if l]
  
          while True:
              context.progress = {}
              context.partials = {}
  
              if self._yield_per:
                  fetch = cursor.fetchmany(self._yield_per)
                  if not fetch:
                      break
              else:
                  fetch = cursor.fetchall()
  
              if custom_rows:
                  rows = []
                  for row in fetch:
                      process[0](row, rows)
              elif single_entity:
                  rows = [process[0](row, None) for row in fetch]
              else:
                  rows = [util.NamedTuple([proc(row, None) for proc in process],
                                          labels) for row in fetch]
  
              if filter:
                  rows = filter(rows)
  
              if context.refresh_state and self._only_load_props \
                          and context.refresh_state in context.progress:
                  context.refresh_state.commit(
                          context.refresh_state.dict, self._only_load_props)
                  context.progress.pop(context.refresh_state)
  
              session._finalize_loaded(context.progress)
  
              for ii, (dict_, attrs) in context.partials.iteritems():
                  ii.commit(dict_, attrs)
  
              for row in rows:
                  yield row
  
              if not self._yield_per:
                  break
  
      def merge_result(self, iterator, load=True):
          """Merge a result into this Query's Session.
          
          Given an iterator returned by a Query of the same structure as this
          one, return an identical iterator of results, with all mapped
          instances merged into the session using Session.merge(). This is an
          optimized method which will merge all mapped instances, preserving the
          structure of the result rows and unmapped columns with less method
          overhead than that of calling Session.merge() explicitly for each
          value.
          
          The structure of the results is determined based on the column list of
          this Query - if these do not correspond, unchecked errors will occur.
          
          The 'load' argument is the same as that of Session.merge().
          
          """
          
          session = self.session
          if load:
              # flush current contents if we expect to load data
              session._autoflush()
              
          autoflush = session.autoflush
          try:
              session.autoflush = False
              single_entity = len(self._entities) == 1
              if single_entity:
                  if isinstance(self._entities[0], _MapperEntity):
                      result = [session._merge(
                              attributes.instance_state(instance), 
                              attributes.instance_dict(instance), 
                              load=load, _recursive={})
                              for instance in iterator]
                  else:
                      result = list(iterator)
              else:
                  mapped_entities = [i for i, e in enumerate(self._entities) 
                                          if isinstance(e, _MapperEntity)]
                  result = []
                  for row in iterator:
                      newrow = list(row)
                      for i in mapped_entities:
                          newrow[i] = session._merge(
                                  attributes.instance_state(newrow[i]), 
                                  attributes.instance_dict(newrow[i]), 
                                  load=load, _recursive={})
                      result.append(util.NamedTuple(newrow, row._labels))  
              
              return iter(result)
          finally:
              session.autoflush = autoflush
          
          
      def _get(self, key=None, ident=None, refresh_state=None, lockmode=None,
                                          only_load_props=None, passive=None):
          lockmode = lockmode or self._lockmode
          
          mapper = self._mapper_zero()
          if not self._populate_existing and \
                  not refresh_state and \
                  not mapper.always_refresh and \
                  lockmode is None:
              instance = self.session.identity_map.get(key)
              if instance:
                  # item present in identity map with a different class
                  if not issubclass(instance.__class__, mapper.class_):
                      return None
                      
                  state = attributes.instance_state(instance)
                  
                  # expired - ensure it still exists
                  if state.expired:
                      if passive is attributes.PASSIVE_NO_FETCH:
                          return attributes.PASSIVE_NO_RESULT
                      try:
                          state()
                      except orm_exc.ObjectDeletedError:
                          self.session._remove_newly_deleted(state)
                          return None
                  return instance
              elif passive is attributes.PASSIVE_NO_FETCH:
                  return attributes.PASSIVE_NO_RESULT
  
          if ident is None:
              if key is not None:
                  ident = key[1]
          else:
              ident = util.to_list(ident)
  
          if refresh_state is None:
              q = self._clone()
              q._get_condition()
          else:
              q = self._clone()
  
          if ident is not None:
              (_get_clause, _get_params) = mapper._get_clause
              
              # None present in ident - turn those comparisons
              # into "IS NULL"
              if None in ident:
                  nones = set([
                              _get_params[col].key for col, value in
                               zip(mapper.primary_key, ident) if value is None
                              ])
                  _get_clause = sql_util.adapt_criterion_to_null(
                                                  _get_clause, nones)
                  
              _get_clause = q._adapt_clause(_get_clause, True, False)
              q._criterion = _get_clause
  
              params = dict([
                  (_get_params[primary_key].key, id_val)
                  for id_val, primary_key in zip(ident, mapper.primary_key)
              ])
  
              if len(params) != len(mapper.primary_key):
                  raise sa_exc.InvalidRequestError(
                  "Incorrect number of values in identifier to formulate "
                  "primary key for query.get(); primary key columns are %s" %
                  ','.join("'%s'" % c for c in mapper.primary_key))
                          
              q._params = params
  
          if lockmode is not None:
              q._lockmode = lockmode
          q._get_options(
              populate_existing=bool(refresh_state),
              version_check=(lockmode is not None),
              only_load_props=only_load_props,
              refresh_state=refresh_state)
          q._order_by = None
  
          try:
              return q.one()
          except orm_exc.NoResultFound:
              return None
  
      @property
      def _select_args(self):
          return {
              'limit':self._limit,
              'offset':self._offset,
              'distinct':self._distinct,
              'group_by':self._group_by or None,
              'having':self._having
          }
  
      @property
      def _should_nest_selectable(self):
          kwargs = self._select_args
          return (kwargs.get('limit') is not None or
                  kwargs.get('offset') is not None or
                  kwargs.get('distinct', False))
  
      def count(self):
          """Return a count of rows this Query would return.
          
          For simple entity queries, count() issues
          a SELECT COUNT, and will specifically count the primary
          key column of the first entity only.  If the query uses 
          LIMIT, OFFSET, or DISTINCT, count() will wrap the statement 
          generated by this Query in a subquery, from which a SELECT COUNT
          is issued, so that the contract of "how many rows
          would be returned?" is honored.
          
          For queries that request specific columns or expressions, 
          count() again makes no assumptions about those expressions
          and will wrap everything in a subquery.  Therefore,
          ``Query.count()`` is usually not what you want in this case.   
          To count specific columns, often in conjunction with 
          GROUP BY, use ``func.count()`` as an individual column expression
          instead of ``Query.count()``.  See the ORM tutorial
          for an example.
  
          """
          should_nest = [self._should_nest_selectable]
          def ent_cols(ent):
              if isinstance(ent, _MapperEntity):
                  return ent.mapper.primary_key
              else:
                  should_nest[0] = True
                  return [ent.column]
  
          return self._col_aggregate(sql.literal_column('1'), sql.func.count,
              nested_cols=chain(*[ent_cols(ent) for ent in self._entities]),
              should_nest = should_nest[0]
          )
  
      def _col_aggregate(self, col, func, nested_cols=None, should_nest=False):
          context = QueryContext(self)
  
          for entity in self._entities:
              entity.setup_context(self, context)
  
          if context.from_clause:
              from_obj = list(context.from_clause)
          else:
              from_obj = context.froms
  
          self._adjust_for_single_inheritance(context)
  
          whereclause  = context.whereclause
  
          if should_nest:
              if not nested_cols:
                  nested_cols = [col]
              else:
                  nested_cols = list(nested_cols)
              s = sql.select(nested_cols, whereclause, 
                          from_obj=from_obj, use_labels=True,
                          **self._select_args)
              s = s.alias()
              s = sql.select(
                  [func(s.corresponding_column(col) or col)]).select_from(s)
          else:
              s = sql.select([func(col)], whereclause, from_obj=from_obj,
              **self._select_args)
  
          if self._autoflush and not self._populate_existing:
              self.session._autoflush()
          return self.session.scalar(s, params=self._params,
              mapper=self._mapper_zero())
  
      def delete(self, synchronize_session='evaluate'):
          """Perform a bulk delete query.
  
          Deletes rows matched by this query from the database.
  
          :param synchronize_session: chooses the strategy for the removal of
              matched objects from the session. Valid values are:
          
              False - don't synchronize the session. This option is the most
              efficient and is reliable once the session is expired, which
              typically occurs after a commit(), or explicitly using
              expire_all(). Before the expiration, objects may still remain in
              the session which were in fact deleted which can lead to confusing
              results if they are accessed via get() or already loaded
              collections.
  
              'fetch' - performs a select query before the delete to find
              objects that are matched by the delete query and need to be
              removed from the session. Matched objects are removed from the
              session.
  
              'evaluate' - Evaluate the query's criteria in Python straight on
              the objects in the session. If evaluation of the criteria isn't
              implemented, an error is raised.  In that case you probably 
              want to use the 'fetch' strategy as a fallback.
            
              The expression evaluator currently doesn't account for differing
              string collations between the database and Python.
  
          Returns the number of rows deleted, excluding any cascades.
  
          The method does *not* offer in-Python cascading of relationships - it
          is assumed that ON DELETE CASCADE is configured for any foreign key
          references which require it. The Session needs to be expired (occurs
          automatically after commit(), or call expire_all()) in order for the
          state of dependent objects subject to delete or delete-orphan cascade
          to be correctly represented.
  
          Also, the ``before_delete()`` and ``after_delete()``
          :class:`~sqlalchemy.orm.interfaces.MapperExtension` methods are not
          called from this method. For a delete hook here, use the
          ``after_bulk_delete()``
          :class:`~sqlalchemy.orm.interfaces.MapperExtension` method.
  
          """
          #TODO: lots of duplication and ifs - probably needs to be 
          # refactored to strategies
          #TODO: cascades need handling.
  
          if synchronize_session not in [False, 'evaluate', 'fetch']:
              raise sa_exc.ArgumentError(
                              "Valid strategies for session "
                              "synchronization are False, 'evaluate' and "
                              "'fetch'")
          self._no_select_modifiers("delete")
  
          self = self.enable_eagerloads(False)
  
          context = self._compile_context()
          if len(context.statement.froms) != 1 or \
                      not isinstance(context.statement.froms[0], schema.Table):
              raise sa_exc.ArgumentError("Only deletion via a single table "
                                          "query is currently supported")
          primary_table = context.statement.froms[0]
  
          session = self.session
  
          if synchronize_session == 'evaluate':
              try:
                  evaluator_compiler = evaluator.EvaluatorCompiler()
                  if self.whereclause is not None:
                      eval_condition = evaluator_compiler.process(
                                                              self.whereclause)
                  else:
                      def eval_condition(obj):
                          return True
                      
              except evaluator.UnevaluatableError:
                  raise sa_exc.InvalidRequestError(
                      "Could not evaluate current criteria in Python.  "
                      "Specify 'fetch' or False for the synchronize_session "
                      "parameter.")
  
          delete_stmt = sql.delete(primary_table, context.whereclause)
  
          if synchronize_session == 'fetch':
              #TODO: use RETURNING when available
              select_stmt = context.statement.with_only_columns(
                                                  primary_table.primary_key)
              matched_rows = session.execute(
                                          select_stmt,
                                          params=self._params).fetchall()
  
          if self._autoflush:
              session._autoflush()
          result = session.execute(delete_stmt, params=self._params)
  
          if synchronize_session == 'evaluate':
              target_cls = self._mapper_zero().class_
  
              #TODO: detect when the where clause is a trivial primary key match
              objs_to_expunge = [
                                  obj for (cls, pk),obj in
                                  session.identity_map.iteritems()
                                  if issubclass(cls, target_cls) and
                                  eval_condition(obj)]
              for obj in objs_to_expunge:
                  session._remove_newly_deleted(attributes.instance_state(obj))
          elif synchronize_session == 'fetch':
              target_mapper = self._mapper_zero()
              for primary_key in matched_rows:
                  identity_key = target_mapper.identity_key_from_primary_key(
                                                              list(primary_key))
                  if identity_key in session.identity_map:
                      session._remove_newly_deleted(
                          attributes.instance_state(
                              session.identity_map[identity_key]
                          )
                      )
  
          for ext in session.extensions:
              ext.after_bulk_delete(session, self, context, result)
  
          return result.rowcount
  
      def update(self, values, synchronize_session='evaluate'):
          """Perform a bulk update query.
  
          Updates rows matched by this query in the database.
  
          :param values: a dictionary with attributes names as keys and literal
            values or sql expressions as values.
  
          :param synchronize_session: chooses the strategy to update the
              attributes on objects in the session. Valid values are:
  
              False - don't synchronize the session. This option is the most
              efficient and is reliable once the session is expired, which
              typically occurs after a commit(), or explicitly using
              expire_all(). Before the expiration, updated objects may still
              remain in the session with stale values on their attributes, which
              can lead to confusing results.
                
              'fetch' - performs a select query before the update to find
              objects that are matched by the update query. The updated
              attributes are expired on matched objects.
  
              'evaluate' - Evaluate the Query's criteria in Python straight on
              the objects in the session. If evaluation of the criteria isn't
              implemented, an exception is raised.
  
              The expression evaluator currently doesn't account for differing
              string collations between the database and Python.
  
          Returns the number of rows matched by the update.
  
          The method does *not* offer in-Python cascading of relationships - it
          is assumed that ON UPDATE CASCADE is configured for any foreign key
          references which require it.
  
          The Session needs to be expired (occurs automatically after commit(),
          or call expire_all()) in order for the state of dependent objects
          subject foreign key cascade to be correctly represented.
  
          Also, the ``before_update()`` and ``after_update()``
          :class:`~sqlalchemy.orm.interfaces.MapperExtension` methods are not
          called from this method. For an update hook here, use the
          ``after_bulk_update()``
          :class:`~sqlalchemy.orm.interfaces.SessionExtension` method.
  
          """
  
          #TODO: value keys need to be mapped to corresponding sql cols and
          # instr.attr.s to string keys
          #TODO: updates of manytoone relationships need to be converted to 
          # fk assignments
          #TODO: cascades need handling.
  
          if synchronize_session == 'expire':
              util.warn_deprecated("The 'expire' value as applied to "
                                      "the synchronize_session argument of "
                                      "query.update() is now called 'fetch'")
              synchronize_session = 'fetch'
              
          if synchronize_session not in [False, 'evaluate', 'fetch']:
              raise sa_exc.ArgumentError(
                              "Valid strategies for session synchronization "
                              "are False, 'evaluate' and 'fetch'")
          self._no_select_modifiers("update")
  
          self = self.enable_eagerloads(False)
  
          context = self._compile_context()
          if len(context.statement.froms) != 1 or \
                      not isinstance(context.statement.froms[0], schema.Table):
              raise sa_exc.ArgumentError(
                              "Only update via a single table query is "
                              "currently supported")
          primary_table = context.statement.froms[0]
  
          session = self.session
  
          if synchronize_session == 'evaluate':
              try:
                  evaluator_compiler = evaluator.EvaluatorCompiler()
                  if self.whereclause is not None:
                      eval_condition = evaluator_compiler.process(
                                                      self.whereclause)
                  else:
                      def eval_condition(obj):
                          return True
  
                  value_evaluators = {}
                  for key,value in values.iteritems():
                      key = expression._column_as_key(key)
                      value_evaluators[key] = evaluator_compiler.process(
                                          expression._literal_as_binds(value))
              except evaluator.UnevaluatableError:
                  raise sa_exc.InvalidRequestError(
                          "Could not evaluate current criteria in Python. "
                          "Specify 'fetch' or False for the "
                          "synchronize_session parameter.")
  
          update_stmt = sql.update(primary_table, context.whereclause, values)
  
          if synchronize_session == 'fetch':
              select_stmt = context.statement.with_only_columns(
                                                  primary_table.primary_key)
              matched_rows = session.execute(
                                          select_stmt,
                                          params=self._params).fetchall()
  
          if self._autoflush:
              session._autoflush()
          result = session.execute(update_stmt, params=self._params)
  
          if synchronize_session == 'evaluate':
              target_cls = self._mapper_zero().class_
  
              for (cls, pk),obj in session.identity_map.iteritems():
                  evaluated_keys = value_evaluators.keys()
  
                  if issubclass(cls, target_cls) and eval_condition(obj):
                      state, dict_ = attributes.instance_state(obj),\
                                              attributes.instance_dict(obj)
  
                      # only evaluate unmodified attributes
                      to_evaluate = state.unmodified.intersection(
                                                              evaluated_keys)
                      for key in to_evaluate:
                          dict_[key] = value_evaluators[key](obj)
  
                      state.commit(dict_, list(to_evaluate))
  
                      # expire attributes with pending changes 
                      # (there was no autoflush, so they are overwritten)
                      state.expire_attributes(dict_,
                                      set(evaluated_keys).
                                          difference(to_evaluate))
  
          elif synchronize_session == 'fetch':
              target_mapper = self._mapper_zero()
  
              for primary_key in matched_rows:
                  identity_key = target_mapper.identity_key_from_primary_key(
                                                              list(primary_key))
                  if identity_key in session.identity_map:
                      session.expire(
                                  session.identity_map[identity_key], 
                                  [expression._column_as_key(k) for k in values]
                                  )
  
          for ext in session.extensions:
              ext.after_bulk_update(session, self, context, result)
  
          return result.rowcount
  
      def _compile_context(self, labels=True):
          context = QueryContext(self)
  
          if context.statement is not None:
              return context
  
          if self._lockmode:
              try:
                  for_update = {'read': 'read',
                                'update': True,
                                'update_nowait': 'nowait',
                                None: False}[self._lockmode]
              except KeyError:
                  raise sa_exc.ArgumentError(
                              "Unknown lockmode %r" % self._lockmode)
          else:
              for_update = False
  
          for entity in self._entities:
              entity.setup_context(self, context)
          
          for rec in context.create_eager_joins:
              strategy = rec[0]
              strategy(*rec[1:])
              
          eager_joins = context.eager_joins.values()
  
          if context.from_clause:
              # "load from explicit FROMs" mode, 
              # i.e. when select_from() or join() is used
              froms = list(context.from_clause)  
          else:
              # "load from discrete FROMs" mode, 
              # i.e. when each _MappedEntity has its own FROM
              froms = context.froms   
  
          self._adjust_for_single_inheritance(context)
  
          if not context.primary_columns:
              if self._only_load_props:
                  raise sa_exc.InvalidRequestError(
                              "No column-based properties specified for "
                              "refresh operation. Use session.expire() "
                              "to reload collections and related items.")
              else:
                  raise sa_exc.InvalidRequestError(
                              "Query contains no columns with which to "
                              "SELECT from.")
  
          if context.multi_row_eager_loaders and self._should_nest_selectable:
              # for eager joins present and LIMIT/OFFSET/DISTINCT, 
              # wrap the query inside a select,
              # then append eager joins onto that
  
              if context.order_by:
                  order_by_col_expr = list(
                                          chain(*[
                                              sql_util.find_columns(o) 
                                              for o in context.order_by
                                          ])
                                      )
              else:
                  context.order_by = None
                  order_by_col_expr = []
  
              inner = sql.select(
                          context.primary_columns + order_by_col_expr,
                          context.whereclause,
                          from_obj=froms,
                          use_labels=labels,
                          correlate=False,
                          order_by=context.order_by,
                          **self._select_args
                      )
              
              for hint in self._with_hints:
                  inner = inner.with_hint(*hint)
                  
              if self._correlate:
                  inner = inner.correlate(*self._correlate)
  
              inner = inner.alias()
  
              equivs = self.__all_equivs()
  
              context.adapter = sql_util.ColumnAdapter(inner, equivs)
  
              statement = sql.select(
                                  [inner] + context.secondary_columns, 
                                  for_update=for_update, 
                                  use_labels=labels)
                                  
              if self._execution_options:
                  statement = statement.execution_options(
                                                  **self._execution_options)
  
              from_clause = inner
              for eager_join in eager_joins:
                  # EagerLoader places a 'stop_on' attribute on the join,
                  # giving us a marker as to where the "splice point" of 
                  # the join should be
                  from_clause = sql_util.splice_joins(
                                              from_clause, 
                                              eager_join, eager_join.stop_on)
  
              statement.append_from(from_clause)
  
              if context.order_by:
                      statement.append_order_by(
                          *context.adapter.copy_and_process(
                              context.order_by
                          )
                      )
  
              statement.append_order_by(*context.eager_order_by)
          else:
              if not context.order_by:
                  context.order_by = None
  
              if self._distinct and context.order_by:
                  order_by_col_expr = list(
                                          chain(*[
                                              sql_util.find_columns(o) 
                                              for o in context.order_by
                                          ])
                                      )
                  context.primary_columns += order_by_col_expr
  
              froms += tuple(context.eager_joins.values())
  
              statement = sql.select(
                              context.primary_columns +
                                      context.secondary_columns,
                              context.whereclause,
                              from_obj=froms,
                              use_labels=labels,
                              for_update=for_update,
                              correlate=False,
                              order_by=context.order_by,
                              **self._select_args
                          )
  
              for hint in self._with_hints:
                  statement = statement.with_hint(*hint)
                          
              if self._execution_options:
                  statement = statement.execution_options(
                                              **self._execution_options)
  
              if self._correlate:
                  statement = statement.correlate(*self._correlate)
  
              if context.eager_order_by:
                  statement.append_order_by(*context.eager_order_by)
  
          context.statement = statement
  
          return context
  
      def _adjust_for_single_inheritance(self, context):
          """Apply single-table-inheritance filtering.
  
          For all distinct single-table-inheritance mappers represented in the
          columns clause of this query, add criterion to the WHERE clause of the
          given QueryContext such that only the appropriate subtypes are
          selected from the total results.
  
          """
          for entity, (mapper, adapter, s, i, w) in \
                              self._mapper_adapter_map.iteritems():
              single_crit = mapper._single_table_criterion
              if single_crit is not None:
                  if adapter:
                      single_crit = adapter.traverse(single_crit)
                  single_crit = self._adapt_clause(single_crit, False, False)
                  context.whereclause = sql.and_(
                                              context.whereclause, single_crit)
  
      def __str__(self):
          return str(self._compile_context().statement)
  
  
  class _QueryEntity(object):
      """represent an entity column returned within a Query result."""
  
      def __new__(cls, *args, **kwargs):
          if cls is _QueryEntity:
              entity = args[1]
              if not isinstance(entity, basestring) and \
                          _is_mapped_class(entity):
                  cls = _MapperEntity
              else:
                  cls = _ColumnEntity
          return object.__new__(cls)
  
      def _clone(self):
          q = self.__class__.__new__(self.__class__)
          q.__dict__ = self.__dict__.copy()
          return q
  
  class _MapperEntity(_QueryEntity):
      """mapper/class/AliasedClass entity"""
  
      def __init__(self, query, entity):
          self.primary_entity = not query._entities
          query._entities.append(self)
  
          self.entities = [entity]
          self.entity_zero = self.expr = entity
          
      def setup_entity(self, entity, mapper, adapter, 
                          from_obj, is_aliased_class, with_polymorphic):
          self.mapper = mapper
          self.extension = self.mapper.extension
          self.adapter = adapter
          self.selectable  = from_obj
          self._with_polymorphic = with_polymorphic
          self._polymorphic_discriminator = None
          self.is_aliased_class = is_aliased_class
          if is_aliased_class:
              self.path_entity = self.entity = self.entity_zero = entity
              self._label_name = self.entity._sa_label_name
          else:
              self.path_entity = mapper
              self.entity = self.entity_zero = mapper
              self._label_name = self.mapper.class_.__name__
              
      def set_with_polymorphic(self, query, cls_or_mappers, 
                                  selectable, discriminator):
          if cls_or_mappers is None:
              query._reset_polymorphic_adapter(self.mapper)
              return
  
          mappers, from_obj = self.mapper._with_polymorphic_args(
                                                  cls_or_mappers, selectable)
          self._with_polymorphic = mappers
          self._polymorphic_discriminator = discriminator
  
          # TODO: do the wrapped thing here too so that 
          # with_polymorphic() can be applied to aliases
          if not self.is_aliased_class:
              self.selectable = from_obj
              self.adapter = query._get_polymorphic_adapter(self, from_obj)
  
      @property
      def type(self):
          return self.mapper.class_
  
      def corresponds_to(self, entity):
          if _is_aliased_class(entity) or self.is_aliased_class:
              return entity is self.path_entity
          else:
              return entity.common_parent(self.path_entity)
  
      def adapt_to_selectable(self, query, sel):
          query._entities.append(self)
  
      def _get_entity_clauses(self, query, context):
              
          adapter = None
          if not self.is_aliased_class and query._polymorphic_adapters:
              adapter = query._polymorphic_adapters.get(self.mapper, None)
  
          if not adapter and self.adapter:
              adapter = self.adapter
          
          if adapter:
              if query._from_obj_alias:
                  ret = adapter.wrap(query._from_obj_alias)
              else:
                  ret = adapter
          else:
              ret = query._from_obj_alias
  
          return ret
  
      def row_processor(self, query, context, custom_rows):
          adapter = self._get_entity_clauses(query, context)
  
          if context.adapter and adapter:
              adapter = adapter.wrap(context.adapter)
          elif not adapter:
              adapter = context.adapter
  
          # polymorphic mappers which have concrete tables in 
          # their hierarchy usually
          # require row aliasing unconditionally.
          if not adapter and self.mapper._requires_row_aliasing:
              adapter = sql_util.ColumnAdapter(
                                          self.selectable,
                                          self.mapper._equivalent_columns)
  
          if self.primary_entity:
              _instance = self.mapper._instance_processor(
                                  context, 
                                  (self.path_entity,), 
                                  adapter,
                                  extension=self.extension,
                                  only_load_props=query._only_load_props,
                                  refresh_state=context.refresh_state,
                                  polymorphic_discriminator=
                                      self._polymorphic_discriminator
              )
          else:
              _instance = self.mapper._instance_processor(
                                  context, 
                                  (self.path_entity,), 
                                  adapter,
                                  polymorphic_discriminator=
                                      self._polymorphic_discriminator)
  
          return _instance, self._label_name
      
      def setup_context(self, query, context):
          adapter = self._get_entity_clauses(query, context)
  
          context.froms += (self.selectable,)
  
          if context.order_by is False and self.mapper.order_by:
              context.order_by = self.mapper.order_by
  
              # apply adaptation to the mapper's order_by if needed.
              if adapter:
                  context.order_by = adapter.adapt_list(
                                          util.to_list(
                                              context.order_by
                                          )
                                      )
  
          if self._with_polymorphic:
              poly_properties = self.mapper._iterate_polymorphic_properties(
                  self._with_polymorphic)
          else:
              poly_properties = self.mapper._polymorphic_properties
          for value in poly_properties:
              if query._only_load_props and \
                      value.key not in query._only_load_props:
                  continue
              value.setup(
                  context,
                  self,
                  (self.path_entity,),
                  adapter,
                  only_load_props=query._only_load_props,
                  column_collection=context.primary_columns
              )
  
          if self._polymorphic_discriminator is not None:
              if adapter:
                  pd = adapter.columns[self._polymorphic_discriminator]
              else:
                  pd = self._polymorphic_discriminator
              context.primary_columns.append(pd)
  
      def __str__(self):
          return str(self.mapper)
  
  class _ColumnEntity(_QueryEntity):
      """Column/expression based entity."""
  
      def __init__(self, query, column):
          self.expr = column
          
          if isinstance(column, basestring):
              column = sql.literal_column(column)
              self._label_name = column.name
          elif isinstance(column, attributes.QueryableAttribute):
              self._label_name = column.key
              column = column.__clause_element__()
          else:
              self._label_name = getattr(column, 'key', None)
  
          if not isinstance(column, expression.ColumnElement) and \
                              hasattr(column, '_select_iterable'):
              for c in column._select_iterable:
                  if c is column:
                      break
                  _ColumnEntity(query, c)
  
              if c is not column:
                  return
  
          if not isinstance(column, sql.ColumnElement):
              raise sa_exc.InvalidRequestError(
                  "SQL expression, column, or mapped entity "
                  "expected - got '%r'" % column
              )
  
          # if the Column is unnamed, give it a
          # label() so that mutable column expressions
          # can be located in the result even
          # if the expression's identity has been changed
          # due to adaption
          if not column._label:
              column = column.label(None)
  
          query._entities.append(self)
  
          self.column = column
          self.froms = set()
  
          # look for ORM entities represented within the
          # given expression.  Try to count only entities
          # for columns whos FROM object is in the actual list
          # of FROMs for the overall expression - this helps
          # subqueries which were built from ORM constructs from
          # leaking out their entities into the main select construct
          actual_froms = set(column._from_objects)
  
          self.entities = util.OrderedSet(
              elem._annotations['parententity']
              for elem in visitors.iterate(column, {})
              if 'parententity' in elem._annotations
              and actual_froms.intersection(elem._from_objects)
              )
  
          if self.entities:
              self.entity_zero = list(self.entities)[0]
          else:
              self.entity_zero = None
      
      @property
      def type(self):
          return self.column.type
          
      def adapt_to_selectable(self, query, sel):
          c = _ColumnEntity(query, sel.corresponding_column(self.column))
          c.entity_zero = self.entity_zero
          c.entities = self.entities
          
      def setup_entity(self, entity, mapper, adapter, from_obj,
                                  is_aliased_class, with_polymorphic):
          self.selectable = from_obj
          self.froms.add(from_obj)
  
      def corresponds_to(self, entity):
          if self.entity_zero is None:
              return False
          elif _is_aliased_class(entity):
              return entity is self.entity_zero
          else:
              return not _is_aliased_class(self.entity_zero) and \
                      entity.common_parent(self.entity_zero)
  
      def _resolve_expr_against_query_aliases(self, query, expr, context):
          return query._adapt_clause(expr, False, True)
  
      def row_processor(self, query, context, custom_rows):
          column = self._resolve_expr_against_query_aliases(
                                              query, self.column, context)
  
          if context.adapter:
              column = context.adapter.columns[column]
  
          def proc(row, result):
              return row[column]
  
          return proc, self._label_name
  
      def setup_context(self, query, context):
          column = self._resolve_expr_against_query_aliases(
                                              query, self.column, context)
          context.froms += tuple(self.froms)
          context.primary_columns.append(column)
  
      def __str__(self):
          return str(self.column)
  
  log.class_logger(Query)
  
  class QueryContext(object):
      multi_row_eager_loaders = False
      adapter = None
      froms = ()
      
      def __init__(self, query):
  
          if query._statement is not None:
              if isinstance(query._statement, expression._SelectBaseMixin) and \
                                  not query._statement.use_labels:
                  self.statement = query._statement.apply_labels()
              else:
                  self.statement = query._statement
          else:
              self.statement = None
              self.from_clause = query._from_obj
              self.whereclause = query._criterion
              self.order_by = query._order_by
  
          self.query = query
          self.session = query.session
          self.populate_existing = query._populate_existing
          self.version_check = query._version_check
          self.refresh_state = query._refresh_state
          self.primary_columns = []
          self.secondary_columns = []
          self.eager_order_by = []
          self.eager_joins = {}
          self.create_eager_joins = []
          self.propagate_options = set(o for o in query._with_options if
                                          o.propagate_to_loaders)
          self.attributes = query._attributes.copy()
  
  class AliasOption(interfaces.MapperOption):
  
      def __init__(self, alias):
          self.alias = alias
  
      def process_query(self, query):
          if isinstance(self.alias, basestring):
              alias = query._mapper_zero().mapped_table.alias(self.alias)
          else:
              alias = self.alias
          query._from_obj_alias = sql_util.ColumnAdapter(alias)
  
  
  _runid = 1L
  _id_lock = util.threading.Lock()
  
  def _new_runid():
      global _runid
      _id_lock.acquire()
      try:
          _runid += 1
          return _runid
      finally:
          _id_lock.release()
  