text: # orm/loading.py
  # Copyright (C) 2005-2020 the SQLAlchemy authors and contributors
  # <see AUTHORS file>
  #
  # This module is part of SQLAlchemy and is released under
  # the MIT License: http://www.opensource.org/licenses/mit-license.php
  
  """private module containing functions used to convert database
  rows into object instances and associated state.
  
  the functions here are called primarily by Query, Mapper,
  as well as some of the attribute loading strategies.
  
  """
  from __future__ import absolute_import
  
  from . import attributes
  from . import exc as orm_exc
  from . import path_registry
  from . import strategy_options
  from .base import _DEFER_FOR_STATE
  from .base import _RAISE_FOR_STATE
  from .base import _SET_DEFERRED_EXPIRED
  from .util import _none_set
  from .util import state_str
  from .. import exc as sa_exc
  from .. import future
  from .. import util
  from ..engine import result_tuple
  from ..engine.result import ChunkedIteratorResult
  from ..engine.result import FrozenResult
  from ..engine.result import SimpleResultMetaData
  from ..sql import util as sql_util
  
  _new_runid = util.counter()
  
  
  def instances(cursor, context):
      """Return a :class:`.Result` given an ORM query context.
  
      :param cursor: a :class:`.CursorResult`, generated by a statement
       which came from :class:`.ORMCompileState`
  
      :param context: a :class:`.QueryContext` object
  
      :return: a :class:`.Result` object representing ORM results
  
      .. versionchanged:: 1.4 The instances() function now uses
         :class:`.Result` objects and has an all new interface.
  
      """
  
      context.runid = _new_runid()
      context.post_load_paths = {}
  
      compile_state = context.compile_state
      filtered = compile_state._has_mapper_entities
      single_entity = (
          not context.load_options._only_return_tuples
          and len(compile_state._entities) == 1
          and compile_state._entities[0].supports_single_entity
      )
  
      try:
          (process, labels, extra) = list(
              zip(
                  *[
                      query_entity.row_processor(context, cursor)
                      for query_entity in context.compile_state._entities
                  ]
              )
          )
  
          if context.yield_per and (
              context.loaders_require_buffering
              or context.loaders_require_uniquing
          ):
              raise sa_exc.InvalidRequestError(
                  "Can't use yield_per with eager loaders that require uniquing "
                  "or row buffering, e.g. joinedload() against collections "
                  "or subqueryload().  Consider the selectinload() strategy "
                  "for better flexibility in loading objects."
              )
  
      except Exception:
          with util.safe_reraise():
              cursor.close()
  
      row_metadata = SimpleResultMetaData(
          labels,
          extra,
          _unique_filters=[
              id if ent.use_id_for_hash else None
              for ent in context.compile_state._entities
          ],
      )
  
      def chunks(size):
          while True:
              yield_per = size
  
              context.partials = {}
  
              if yield_per:
                  fetch = cursor.fetchmany(yield_per)
  
                  if not fetch:
                      break
              else:
                  fetch = cursor._raw_all_rows()
  
              if single_entity:
                  proc = process[0]
                  rows = [proc(row) for row in fetch]
              else:
                  rows = [
                      tuple([proc(row) for proc in process]) for row in fetch
                  ]
  
              for path, post_load in context.post_load_paths.items():
                  post_load.invoke(context, path)
  
              yield rows
  
              if not yield_per:
                  break
  
      result = ChunkedIteratorResult(
          row_metadata, chunks, source_supports_scalars=single_entity, raw=cursor
      )
  
      result._attributes = result._attributes.union(
          dict(filtered=filtered, is_single_entity=single_entity)
      )
  
      if context.yield_per:
          result.yield_per(context.yield_per)
  
      return result
  
  
  @util.preload_module("sqlalchemy.orm.context")
  def merge_frozen_result(session, statement, frozen_result, load=True):
      """Merge a :class:`_engine.FrozenResult` back into a :class:`_orm.Session`,
      returning a new :class:`_engine.Result` object with :term:`persistent`
      objects.
  
      See the section :ref:`do_orm_execute_re_executing` for an example.
  
      .. seealso::
  
          :ref:`do_orm_execute_re_executing`
  
          :meth:`_engine.Result.freeze`
  
          :class:`_engine.FrozenResult`
  
      """
      querycontext = util.preloaded.orm_context
  
      if load:
          # flush current contents if we expect to load data
          session._autoflush()
  
      ctx = querycontext.ORMSelectCompileState._create_entities_collection(
          statement
      )
  
      autoflush = session.autoflush
      try:
          session.autoflush = False
          mapped_entities = [
              i
              for i, e in enumerate(ctx._entities)
              if isinstance(e, querycontext._MapperEntity)
          ]
          keys = [ent._label_name for ent in ctx._entities]
  
          keyed_tuple = result_tuple(
              keys, [ent._extra_entities for ent in ctx._entities]
          )
  
          result = []
          for newrow in frozen_result.rewrite_rows():
              for i in mapped_entities:
                  if newrow[i] is not None:
                      newrow[i] = session._merge(
                          attributes.instance_state(newrow[i]),
                          attributes.instance_dict(newrow[i]),
                          load=load,
                          _recursive={},
                          _resolve_conflict_map={},
                      )
  
              result.append(keyed_tuple(newrow))
  
          return frozen_result.with_new_rows(result)
      finally:
          session.autoflush = autoflush
  
  
  @util.deprecated(
      "2.0",
      "The :func:`_orm.merge_result` method is superseded by the "
      ":func:`_orm.merge_frozen_result` function.",
  )
  @util.preload_module("sqlalchemy.orm.context")
  def merge_result(query, iterator, load=True):
      """Merge a result into this :class:`.Query` object's Session."""
  
      querycontext = util.preloaded.orm_context
  
      session = query.session
      if load:
          # flush current contents if we expect to load data
          session._autoflush()
  
      # TODO: need test coverage and documentation for the FrozenResult
      # use case.
      if isinstance(iterator, FrozenResult):
          frozen_result = iterator
          iterator = iter(frozen_result.data)
      else:
          frozen_result = None
  
      ctx = querycontext.ORMSelectCompileState._create_entities_collection(query)
  
      autoflush = session.autoflush
      try:
          session.autoflush = False
          single_entity = not frozen_result and len(ctx._entities) == 1
  
          if single_entity:
              if isinstance(ctx._entities[0], querycontext._MapperEntity):
                  result = [
                      session._merge(
                          attributes.instance_state(instance),
                          attributes.instance_dict(instance),
                          load=load,
                          _recursive={},
                          _resolve_conflict_map={},
                      )
                      for instance in iterator
                  ]
              else:
                  result = list(iterator)
          else:
              mapped_entities = [
                  i
                  for i, e in enumerate(ctx._entities)
                  if isinstance(e, querycontext._MapperEntity)
              ]
              result = []
              keys = [ent._label_name for ent in ctx._entities]
  
              keyed_tuple = result_tuple(
                  keys, [ent._extra_entities for ent in ctx._entities]
              )
  
              for row in iterator:
                  newrow = list(row)
                  for i in mapped_entities:
                      if newrow[i] is not None:
                          newrow[i] = session._merge(
                              attributes.instance_state(newrow[i]),
                              attributes.instance_dict(newrow[i]),
                              load=load,
                              _recursive={},
                              _resolve_conflict_map={},
                          )
                  result.append(keyed_tuple(newrow))
  
          if frozen_result:
              return frozen_result.with_data(result)
          else:
              return iter(result)
      finally:
          session.autoflush = autoflush
  
  
  def get_from_identity(session, mapper, key, passive):
      """Look up the given key in the given session's identity map,
      check the object for expired state if found.
  
      """
      instance = session.identity_map.get(key)
      if instance is not None:
  
          state = attributes.instance_state(instance)
  
          if mapper.inherits and not state.mapper.isa(mapper):
              return attributes.PASSIVE_CLASS_MISMATCH
  
          # expired - ensure it still exists
          if state.expired:
              if not passive & attributes.SQL_OK:
                  # TODO: no coverage here
                  return attributes.PASSIVE_NO_RESULT
              elif not passive & attributes.RELATED_OBJECT_OK:
                  # this mode is used within a flush and the instance's
                  # expired state will be checked soon enough, if necessary
                  return instance
              try:
                  state._load_expired(state, passive)
              except orm_exc.ObjectDeletedError:
                  session._remove_newly_deleted([state])
                  return None
          return instance
      else:
          return None
  
  
  def load_on_ident(
      session,
      statement,
      key,
      load_options=None,
      refresh_state=None,
      with_for_update=None,
      only_load_props=None,
      no_autoflush=False,
      bind_arguments=util.EMPTY_DICT,
      execution_options=util.EMPTY_DICT,
  ):
      """Load the given identity key from the database."""
      if key is not None:
          ident = key[1]
          identity_token = key[2]
      else:
          ident = identity_token = None
  
      return load_on_pk_identity(
          session,
          statement,
          ident,
          load_options=load_options,
          refresh_state=refresh_state,
          with_for_update=with_for_update,
          only_load_props=only_load_props,
          identity_token=identity_token,
          no_autoflush=no_autoflush,
          bind_arguments=bind_arguments,
          execution_options=execution_options,
      )
  
  
  def load_on_pk_identity(
      session,
      statement,
      primary_key_identity,
      load_options=None,
      refresh_state=None,
      with_for_update=None,
      only_load_props=None,
      identity_token=None,
      no_autoflush=False,
      bind_arguments=util.EMPTY_DICT,
      execution_options=util.EMPTY_DICT,
  ):
  
      """Load the given primary key identity from the database."""
  
      query = statement
      q = query._clone()
  
      is_lambda = q._is_lambda_element
  
      # TODO: fix these imports ....
      from .context import QueryContext, ORMCompileState
  
      if load_options is None:
          load_options = QueryContext.default_load_options
  
      compile_options = ORMCompileState.default_compile_options
  
      if primary_key_identity is not None:
          mapper = query._propagate_attrs["plugin_subject"]
  
          (_get_clause, _get_params) = mapper._get_clause
  
          # None present in ident - turn those comparisons
          # into "IS NULL"
          if None in primary_key_identity:
              nones = set(
                  [
                      _get_params[col].key
                      for col, value in zip(
                          mapper.primary_key, primary_key_identity
                      )
                      if value is None
                  ]
              )
  
              _get_clause = sql_util.adapt_criterion_to_null(_get_clause, nones)
  
              if len(nones) == len(primary_key_identity):
                  util.warn(
                      "fully NULL primary key identity cannot load any "
                      "object.  This condition may raise an error in a future "
                      "release."
                  )
  
          if is_lambda:
              q = q.add_criteria(
                  lambda q: q.where(
                      sql_util._deep_annotate(_get_clause, {"_orm_adapt": True})
                  ),
              )
          else:
              q._where_criteria = (
                  sql_util._deep_annotate(_get_clause, {"_orm_adapt": True}),
              )
  
          params = dict(
              [
                  (_get_params[primary_key].key, id_val)
                  for id_val, primary_key in zip(
                      primary_key_identity, mapper.primary_key
                  )
              ]
          )
      else:
          params = None
  
      if is_lambda:
          if with_for_update is not None or refresh_state or only_load_props:
              raise NotImplementedError(
                  "refresh operation not supported with lambda statement"
              )
  
          version_check = False
  
          _, load_options = _set_get_options(
              compile_options,
              load_options,
              populate_existing=bool(refresh_state),
              version_check=version_check,
              only_load_props=only_load_props,
              refresh_state=refresh_state,
              identity_token=identity_token,
          )
  
          if no_autoflush:
              load_options += {"_autoflush": False}
      else:
          if with_for_update is not None:
              version_check = True
              q._for_update_arg = with_for_update
          elif query._for_update_arg is not None:
              version_check = True
              q._for_update_arg = query._for_update_arg
          else:
              version_check = False
  
          if refresh_state and refresh_state.load_options:
              compile_options += {
                  "_current_path": refresh_state.load_path.parent
              }
              q = q.options(*refresh_state.load_options)
  
          # TODO: most of the compile_options that are not legacy only involve
          # this function, so try to see if handling of them can mostly be local
          # to here
  
          q._compile_options, load_options = _set_get_options(
              compile_options,
              load_options,
              populate_existing=bool(refresh_state),
              version_check=version_check,
              only_load_props=only_load_props,
              refresh_state=refresh_state,
              identity_token=identity_token,
          )
          q._order_by = None
  
          if no_autoflush:
              load_options += {"_autoflush": False}
  
      execution_options = util.EMPTY_DICT.merge_with(
          execution_options, {"_sa_orm_load_options": load_options}
      )
      result = (
          session.execute(
              q,
              params=params,
              execution_options=execution_options,
              bind_arguments=bind_arguments,
              future=True,
          )
          .unique()
          .scalars()
      )
  
      try:
          return result.one()
      except orm_exc.NoResultFound:
          return None
  
  
  def _set_get_options(
      compile_opt,
      load_opt,
      populate_existing=None,
      version_check=None,
      only_load_props=None,
      refresh_state=None,
      identity_token=None,
  ):
  
      compile_options = {}
      load_options = {}
      if version_check:
          load_options["_version_check"] = version_check
      if populate_existing:
          load_options["_populate_existing"] = populate_existing
      if refresh_state:
          load_options["_refresh_state"] = refresh_state
          compile_options["_for_refresh_state"] = True
      if only_load_props:
          compile_options["_only_load_props"] = frozenset(only_load_props)
      if identity_token:
          load_options["_refresh_identity_token"] = identity_token
  
      if load_options:
          load_opt += load_options
      if compile_options:
          compile_opt += compile_options
  
      return compile_opt, load_opt
  
  
  def _setup_entity_query(
      compile_state,
      mapper,
      query_entity,
      path,
      adapter,
      column_collection,
      with_polymorphic=None,
      only_load_props=None,
      polymorphic_discriminator=None,
      **kw
  ):
  
      if with_polymorphic:
          poly_properties = mapper._iterate_polymorphic_properties(
              with_polymorphic
          )
      else:
          poly_properties = mapper._polymorphic_properties
  
      quick_populators = {}
  
      path.set(compile_state.attributes, "memoized_setups", quick_populators)
  
      # for the lead entities in the path, e.g. not eager loads, and
      # assuming a user-passed aliased class, e.g. not a from_self() or any
      # implicit aliasing, don't add columns to the SELECT that aren't
      # in the thing that's aliased.
      check_for_adapt = adapter and len(path) == 1 and path[-1].is_aliased_class
  
      for value in poly_properties:
          if only_load_props and value.key not in only_load_props:
              continue
  
          value.setup(
              compile_state,
              query_entity,
              path,
              adapter,
              only_load_props=only_load_props,
              column_collection=column_collection,
              memoized_populators=quick_populators,
              check_for_adapt=check_for_adapt,
              **kw
          )
  
      if (
          polymorphic_discriminator is not None
          and polymorphic_discriminator is not mapper.polymorphic_on
      ):
  
          if adapter:
              pd = adapter.columns[polymorphic_discriminator]
          else:
              pd = polymorphic_discriminator
          column_collection.append(pd)
  
  
  def _warn_for_runid_changed(state):
      util.warn(
          "Loading context for %s has changed within a load/refresh "
          "handler, suggesting a row refresh operation took place. If this "
          "event handler is expected to be "
          "emitting row refresh operations within an existing load or refresh "
          "operation, set restore_load_context=True when establishing the "
          "listener to ensure the context remains unchanged when the event "
          "handler completes." % (state_str(state),)
      )
  
  
  def _instance_processor(
      query_entity,
      mapper,
      context,
      result,
      path,
      adapter,
      only_load_props=None,
      refresh_state=None,
      polymorphic_discriminator=None,
      _polymorphic_from=None,
  ):
      """Produce a mapper level row processor callable
         which processes rows into mapped instances."""
  
      # note that this method, most of which exists in a closure
      # called _instance(), resists being broken out, as
      # attempts to do so tend to add significant function
      # call overhead.  _instance() is the most
      # performance-critical section in the whole ORM.
  
      identity_class = mapper._identity_class
      compile_state = context.compile_state
  
      # look for "row getter" functions that have been assigned along
      # with the compile state that were cached from a previous load.
      # these are operator.itemgetter() objects that each will extract a
      # particular column from each row.
  
      getter_key = ("getters", mapper)
      getters = path.get(compile_state.attributes, getter_key, None)
  
      if getters is None:
          # no getters, so go through a list of attributes we are loading for,
          # and the ones that are column based will have already put information
          # for us in another collection "memoized_setups", which represents the
          # output of the LoaderStrategy.setup_query() method.  We can just as
          # easily call LoaderStrategy.create_row_processor for each, but by
          # getting it all at once from setup_query we save another method call
          # per attribute.
          props = mapper._prop_set
          if only_load_props is not None:
              props = props.intersection(
                  mapper._props[k] for k in only_load_props
              )
  
          quick_populators = path.get(
              context.attributes, "memoized_setups", _none_set
          )
  
          todo = []
          cached_populators = {
              "new": [],
              "quick": [],
              "deferred": [],
              "expire": [],
              "delayed": [],
              "existing": [],
              "eager": [],
          }
  
          if refresh_state is None:
              # we can also get the "primary key" tuple getter function
              pk_cols = mapper.primary_key
  
              if adapter:
                  pk_cols = [adapter.columns[c] for c in pk_cols]
              primary_key_getter = result._tuple_getter(pk_cols)
          else:
              primary_key_getter = None
  
          getters = {
              "cached_populators": cached_populators,
              "todo": todo,
              "primary_key_getter": primary_key_getter,
          }
          for prop in props:
              if prop in quick_populators:
                  # this is an inlined path just for column-based attributes.
                  col = quick_populators[prop]
                  if col is _DEFER_FOR_STATE:
                      cached_populators["new"].append(
                          (prop.key, prop._deferred_column_loader)
                      )
                  elif col is _SET_DEFERRED_EXPIRED:
                      # note that in this path, we are no longer
                      # searching in the result to see if the column might
                      # be present in some unexpected way.
                      cached_populators["expire"].append((prop.key, False))
                  elif col is _RAISE_FOR_STATE:
                      cached_populators["new"].append(
                          (prop.key, prop._raise_column_loader)
                      )
                  else:
                      getter = None
                      if not getter:
                          getter = result._getter(col, False)
                      if getter:
                          cached_populators["quick"].append((prop.key, getter))
                      else:
                          # fall back to the ColumnProperty itself, which
                          # will iterate through all of its columns
                          # to see if one fits
                          prop.create_row_processor(
                              context,
                              query_entity,
                              path,
                              mapper,
                              result,
                              adapter,
                              cached_populators,
                          )
              else:
                  # loader strategies like subqueryload, selectinload,
                  # joinedload, basically relationships, these need to interact
                  # with the context each time to work correctly.
                  todo.append(prop)
  
          path.set(compile_state.attributes, getter_key, getters)
  
      cached_populators = getters["cached_populators"]
  
      populators = {key: list(value) for key, value in cached_populators.items()}
      for prop in getters["todo"]:
          prop.create_row_processor(
              context, query_entity, path, mapper, result, adapter, populators
          )
  
      propagated_loader_options = context.propagated_loader_options
      load_path = (
          context.compile_state.current_path + path
          if context.compile_state.current_path.path
          else path
      )
  
      session_identity_map = context.session.identity_map
  
      populate_existing = context.populate_existing or mapper.always_refresh
      load_evt = bool(mapper.class_manager.dispatch.load)
      refresh_evt = bool(mapper.class_manager.dispatch.refresh)
      persistent_evt = bool(context.session.dispatch.loaded_as_persistent)
      if persistent_evt:
          loaded_as_persistent = context.session.dispatch.loaded_as_persistent
      instance_state = attributes.instance_state
      instance_dict = attributes.instance_dict
      session_id = context.session.hash_key
      runid = context.runid
      identity_token = context.identity_token
  
      version_check = context.version_check
      if version_check:
          version_id_col = mapper.version_id_col
          if version_id_col is not None:
              if adapter:
                  version_id_col = adapter.columns[version_id_col]
              version_id_getter = result._getter(version_id_col)
          else:
              version_id_getter = None
  
      if not refresh_state and _polymorphic_from is not None:
          key = ("loader", path.path)
          if key in context.attributes and context.attributes[key].strategy == (
              ("selectinload_polymorphic", True),
          ):
              selectin_load_via = mapper._should_selectin_load(
                  context.attributes[key].local_opts["entities"],
                  _polymorphic_from,
              )
          else:
              selectin_load_via = mapper._should_selectin_load(
                  None, _polymorphic_from
              )
  
          if selectin_load_via and selectin_load_via is not _polymorphic_from:
              # only_load_props goes w/ refresh_state only, and in a refresh
              # we are a single row query for the exact entity; polymorphic
              # loading does not apply
              assert only_load_props is None
  
              callable_ = _load_subclass_via_in(context, path, selectin_load_via)
  
              PostLoad.callable_for_path(
                  context,
                  load_path,
                  selectin_load_via.mapper,
                  selectin_load_via,
                  callable_,
                  selectin_load_via,
              )
  
      post_load = PostLoad.for_context(context, load_path, only_load_props)
  
      if refresh_state:
          refresh_identity_key = refresh_state.key
          if refresh_identity_key is None:
              # super-rare condition; a refresh is being called
              # on a non-instance-key instance; this is meant to only
              # occur within a flush()
              refresh_identity_key = mapper._identity_key_from_state(
                  refresh_state
              )
      else:
          refresh_identity_key = None
  
          primary_key_getter = getters["primary_key_getter"]
  
      if mapper.allow_partial_pks:
          is_not_primary_key = _none_set.issuperset
      else:
          is_not_primary_key = _none_set.intersection
  
      def _instance(row):
  
          # determine the state that we'll be populating
          if refresh_identity_key:
              # fixed state that we're refreshing
              state = refresh_state
              instance = state.obj()
              dict_ = instance_dict(instance)
              isnew = state.runid != runid
              currentload = True
              loaded_instance = False
          else:
              # look at the row, see if that identity is in the
              # session, or we have to create a new one
              identitykey = (
                  identity_class,
                  primary_key_getter(row),
                  identity_token,
              )
  
              instance = session_identity_map.get(identitykey)
  
              if instance is not None:
                  # existing instance
                  state = instance_state(instance)
                  dict_ = instance_dict(instance)
  
                  isnew = state.runid != runid
                  currentload = not isnew
                  loaded_instance = False
  
                  if version_check and version_id_getter and not currentload:
                      _validate_version_id(
                          mapper, state, dict_, row, version_id_getter
                      )
  
              else:
                  # create a new instance
  
                  # check for non-NULL values in the primary key columns,
                  # else no entity is returned for the row
                  if is_not_primary_key(identitykey[1]):
                      return None
  
                  isnew = True
                  currentload = True
                  loaded_instance = True
  
                  instance = mapper.class_manager.new_instance()
  
                  dict_ = instance_dict(instance)
                  state = instance_state(instance)
                  state.key = identitykey
                  state.identity_token = identity_token
  
                  # attach instance to session.
                  state.session_id = session_id
                  session_identity_map._add_unpresent(state, identitykey)
  
          # populate.  this looks at whether this state is new
          # for this load or was existing, and whether or not this
          # row is the first row with this identity.
          if currentload or populate_existing:
              # full population routines.  Objects here are either
              # just created, or we are doing a populate_existing
  
              # be conservative about setting load_path when populate_existing
              # is in effect; want to maintain options from the original
              # load.  see test_expire->test_refresh_maintains_deferred_options
              if isnew and (propagated_loader_options or not populate_existing):
                  state.load_options = propagated_loader_options
                  state.load_path = load_path
  
              _populate_full(
                  context,
                  row,
                  state,
                  dict_,
                  isnew,
                  load_path,
                  loaded_instance,
                  populate_existing,
                  populators,
              )
  
              if isnew:
                  # state.runid should be equal to context.runid / runid
                  # here, however for event checks we are being more conservative
                  # and checking against existing run id
                  # assert state.runid == runid
  
                  existing_runid = state.runid
  
                  if loaded_instance:
                      if load_evt:
                          state.manager.dispatch.load(state, context)
                          if state.runid != existing_runid:
                              _warn_for_runid_changed(state)
                      if persistent_evt:
                          loaded_as_persistent(context.session, state)
                          if state.runid != existing_runid:
                              _warn_for_runid_changed(state)
                  elif refresh_evt:
                      state.manager.dispatch.refresh(
                          state, context, only_load_props
                      )
                      if state.runid != runid:
                          _warn_for_runid_changed(state)
  
                  if populate_existing or state.modified:
                      if refresh_state and only_load_props:
                          state._commit(dict_, only_load_props)
                      else:
                          state._commit_all(dict_, session_identity_map)
  
              if post_load:
                  post_load.add_state(state, True)
  
          else:
              # partial population routines, for objects that were already
              # in the Session, but a row matches them; apply eager loaders
              # on existing objects, etc.
              unloaded = state.unloaded
              isnew = state not in context.partials
  
              if not isnew or unloaded or populators["eager"]:
                  # state is having a partial set of its attributes
                  # refreshed.  Populate those attributes,
                  # and add to the "context.partials" collection.
  
                  to_load = _populate_partial(
                      context,
                      row,
                      state,
                      dict_,
                      isnew,
                      load_path,
                      unloaded,
                      populators,
                  )
  
                  if isnew:
                      if refresh_evt:
                          existing_runid = state.runid
                          state.manager.dispatch.refresh(state, context, to_load)
                          if state.runid != existing_runid:
                              _warn_for_runid_changed(state)
  
                      state._commit(dict_, to_load)
  
              if post_load and context.invoke_all_eagers:
                  post_load.add_state(state, False)
  
          return instance
  
      if mapper.polymorphic_map and not _polymorphic_from and not refresh_state:
          # if we are doing polymorphic, dispatch to a different _instance()
          # method specific to the subclass mapper
          def ensure_no_pk(row):
              identitykey = (
                  identity_class,
                  primary_key_getter(row),
                  identity_token,
              )
              if not is_not_primary_key(identitykey[1]):
                  return identitykey
              else:
                  return None
  
          _instance = _decorate_polymorphic_switch(
              _instance,
              context,
              query_entity,
              mapper,
              result,
              path,
              polymorphic_discriminator,
              adapter,
              ensure_no_pk,
          )
  
      return _instance
  
  
  def _load_subclass_via_in(context, path, entity):
      mapper = entity.mapper
  
      zero_idx = len(mapper.base_mapper.primary_key) == 1
  
      if entity.is_aliased_class:
          q, enable_opt, disable_opt = mapper._subclass_load_via_in(entity)
      else:
          q, enable_opt, disable_opt = mapper._subclass_load_via_in_mapper
  
      def do_load(context, path, states, load_only, effective_entity):
          orig_query = context.query
  
          q2 = q._with_lazyload_options(
              (enable_opt,) + orig_query._with_options + (disable_opt,),
              path.parent,
              cache_path=path,
          )
  
          if context.populate_existing:
              q2.add_criteria(lambda q: q.populate_existing())
  
          q2(context.session).params(
              primary_keys=[
                  state.key[1][0] if zero_idx else state.key[1]
                  for state, load_attrs in states
              ]
          ).all()
  
      return do_load
  
  
  def _populate_full(
      context,
      row,
      state,
      dict_,
      isnew,
      load_path,
      loaded_instance,
      populate_existing,
      populators,
  ):
      if isnew:
          # first time we are seeing a row with this identity.
          state.runid = context.runid
  
          for key, getter in populators["quick"]:
              dict_[key] = getter(row)
          if populate_existing:
              for key, set_callable in populators["expire"]:
                  dict_.pop(key, None)
                  if set_callable:
                      state.expired_attributes.add(key)
          else:
              for key, set_callable in populators["expire"]:
                  if set_callable:
                      state.expired_attributes.add(key)
  
          for key, populator in populators["new"]:
              populator(state, dict_, row)
          for key, populator in populators["delayed"]:
              populator(state, dict_, row)
      elif load_path != state.load_path:
          # new load path, e.g. object is present in more than one
          # column position in a series of rows
          state.load_path = load_path
  
          # if we have data, and the data isn't in the dict, OK, let's put
          # it in.
          for key, getter in populators["quick"]:
              if key not in dict_:
                  dict_[key] = getter(row)
  
          # otherwise treat like an "already seen" row
          for key, populator in populators["existing"]:
              populator(state, dict_, row)
              # TODO:  allow "existing" populator to know this is
              # a new path for the state:
              # populator(state, dict_, row, new_path=True)
  
      else:
          # have already seen rows with this identity in this same path.
          for key, populator in populators["existing"]:
              populator(state, dict_, row)
  
              # TODO: same path
              # populator(state, dict_, row, new_path=False)
  
  
  def _populate_partial(
      context, row, state, dict_, isnew, load_path, unloaded, populators
  ):
  
      if not isnew:
          to_load = context.partials[state]
          for key, populator in populators["existing"]:
              if key in to_load:
                  populator(state, dict_, row)
      else:
          to_load = unloaded
          context.partials[state] = to_load
  
          for key, getter in populators["quick"]:
              if key in to_load:
                  dict_[key] = getter(row)
          for key, set_callable in populators["expire"]:
              if key in to_load:
                  dict_.pop(key, None)
                  if set_callable:
                      state.expired_attributes.add(key)
          for key, populator in populators["new"]:
              if key in to_load:
                  populator(state, dict_, row)
          for key, populator in populators["delayed"]:
              if key in to_load:
                  populator(state, dict_, row)
      for key, populator in populators["eager"]:
          if key not in unloaded:
              populator(state, dict_, row)
  
      return to_load
  
  
  def _validate_version_id(mapper, state, dict_, row, getter):
  
      if mapper._get_state_attr_by_column(
          state, dict_, mapper.version_id_col
      ) != getter(row):
          raise orm_exc.StaleDataError(
              "Instance '%s' has version id '%s' which "
              "does not match database-loaded version id '%s'."
              % (
                  state_str(state),
                  mapper._get_state_attr_by_column(
                      state, dict_, mapper.version_id_col
                  ),
                  getter(row),
              )
          )
  
  
  def _decorate_polymorphic_switch(
      instance_fn,
      context,
      query_entity,
      mapper,
      result,
      path,
      polymorphic_discriminator,
      adapter,
      ensure_no_pk,
  ):
      if polymorphic_discriminator is not None:
          polymorphic_on = polymorphic_discriminator
      else:
          polymorphic_on = mapper.polymorphic_on
      if polymorphic_on is None:
          return instance_fn
  
      if adapter:
          polymorphic_on = adapter.columns[polymorphic_on]
  
      def configure_subclass_mapper(discriminator):
          try:
              sub_mapper = mapper.polymorphic_map[discriminator]
          except KeyError:
              raise AssertionError(
                  "No such polymorphic_identity %r is defined" % discriminator
              )
          else:
              if sub_mapper is mapper:
                  return None
              elif not sub_mapper.isa(mapper):
                  return False
  
              return _instance_processor(
                  query_entity,
                  sub_mapper,
                  context,
                  result,
                  path,
                  adapter,
                  _polymorphic_from=mapper,
              )
  
      polymorphic_instances = util.PopulateDict(configure_subclass_mapper)
  
      getter = result._getter(polymorphic_on)
  
      def polymorphic_instance(row):
          discriminator = getter(row)
          if discriminator is not None:
              _instance = polymorphic_instances[discriminator]
              if _instance:
                  return _instance(row)
              elif _instance is False:
                  identitykey = ensure_no_pk(row)
  
                  if identitykey:
                      raise sa_exc.InvalidRequestError(
                          "Row with identity key %s can't be loaded into an "
                          "object; the polymorphic discriminator column '%s' "
                          "refers to %s, which is not a sub-mapper of "
                          "the requested %s"
                          % (
                              identitykey,
                              polymorphic_on,
                              mapper.polymorphic_map[discriminator],
                              mapper,
                          )
                      )
                  else:
                      return None
              else:
                  return instance_fn(row)
          else:
              identitykey = ensure_no_pk(row)
  
              if identitykey:
                  raise sa_exc.InvalidRequestError(
                      "Row with identity key %s can't be loaded into an "
                      "object; the polymorphic discriminator column '%s' is "
                      "NULL" % (identitykey, polymorphic_on)
                  )
              else:
                  return None
  
      return polymorphic_instance
  
  
  class PostLoad(object):
      """Track loaders and states for "post load" operations.
  
      """
  
      __slots__ = "loaders", "states", "load_keys"
  
      def __init__(self):
          self.loaders = {}
          self.states = util.OrderedDict()
          self.load_keys = None
  
      def add_state(self, state, overwrite):
          # the states for a polymorphic load here are all shared
          # within a single PostLoad object among multiple subtypes.
          # Filtering of callables on a per-subclass basis needs to be done at
          # the invocation level
          self.states[state] = overwrite
  
      def invoke(self, context, path):
          if not self.states:
              return
          path = path_registry.PathRegistry.coerce(path)
          for token, limit_to_mapper, loader, arg, kw in self.loaders.values():
              states = [
                  (state, overwrite)
                  for state, overwrite in self.states.items()
                  if state.manager.mapper.isa(limit_to_mapper)
              ]
              if states:
                  loader(context, path, states, self.load_keys, *arg, **kw)
          self.states.clear()
  
      @classmethod
      def for_context(cls, context, path, only_load_props):
          pl = context.post_load_paths.get(path.path)
          if pl is not None and only_load_props:
              pl.load_keys = only_load_props
          return pl
  
      @classmethod
      def path_exists(self, context, path, key):
          return (
              path.path in context.post_load_paths
              and key in context.post_load_paths[path.path].loaders
          )
  
      @classmethod
      def callable_for_path(
          cls, context, path, limit_to_mapper, token, loader_callable, *arg, **kw
      ):
          if path.path in context.post_load_paths:
              pl = context.post_load_paths[path.path]
          else:
              pl = context.post_load_paths[path.path] = PostLoad()
          pl.loaders[token] = (token, limit_to_mapper, loader_callable, arg, kw)
  
  
  def load_scalar_attributes(mapper, state, attribute_names, passive):
      """initiate a column-based attribute refresh operation."""
  
      # assert mapper is _state_mapper(state)
      session = state.session
      if not session:
          raise orm_exc.DetachedInstanceError(
              "Instance %s is not bound to a Session; "
              "attribute refresh operation cannot proceed" % (state_str(state))
          )
  
      has_key = bool(state.key)
  
      result = False
  
      no_autoflush = bool(passive & attributes.NO_AUTOFLUSH)
  
      # in the case of inheritance, particularly concrete and abstract
      # concrete inheritance, the class manager might have some keys
      # of attributes on the superclass that we didn't actually map.
      # These could be mapped as "concrete, dont load" or could be completely
      # excluded from the mapping and we know nothing about them.  Filter them
      # here to prevent them from coming through.
      if attribute_names:
          attribute_names = attribute_names.intersection(mapper.attrs.keys())
  
      if mapper.inherits and not mapper.concrete:
          # because we are using Core to produce a select() that we
          # pass to the Query, we aren't calling setup() for mapped
          # attributes; in 1.0 this means deferred attrs won't get loaded
          # by default
          statement = mapper._optimized_get_statement(state, attribute_names)
          if statement is not None:
              # this was previously aliased(mapper, statement), however,
              # statement is a select() and Query's coercion now raises for this
              # since you can't "select" from a "SELECT" statement.  only
              # from_statement() allows this.
              # note: using from_statement() here means there is an adaption
              # with adapt_on_names set up.  the other option is to make the
              # aliased() against a subquery which affects the SQL.
  
              from .query import FromStatement
  
              stmt = FromStatement(mapper, statement).options(
                  strategy_options.Load(mapper).undefer("*")
              )
  
              result = load_on_ident(
                  session,
                  stmt,
                  None,
                  only_load_props=attribute_names,
                  refresh_state=state,
                  no_autoflush=no_autoflush,
              )
  
      if result is False:
          if has_key:
              identity_key = state.key
          else:
              # this codepath is rare - only valid when inside a flush, and the
              # object is becoming persistent but hasn't yet been assigned
              # an identity_key.
              # check here to ensure we have the attrs we need.
              pk_attrs = [
                  mapper._columntoproperty[col].key for col in mapper.primary_key
              ]
              if state.expired_attributes.intersection(pk_attrs):
                  raise sa_exc.InvalidRequestError(
                      "Instance %s cannot be refreshed - it's not "
                      " persistent and does not "
                      "contain a full primary key." % state_str(state)
                  )
              identity_key = mapper._identity_key_from_state(state)
  
          if (
              _none_set.issubset(identity_key) and not mapper.allow_partial_pks
          ) or _none_set.issuperset(identity_key):
              util.warn_limited(
                  "Instance %s to be refreshed doesn't "
                  "contain a full primary key - can't be refreshed "
                  "(and shouldn't be expired, either).",
                  state_str(state),
              )
              return
  
          result = load_on_ident(
              session,
              future.select(mapper).apply_labels(),
              identity_key,
              refresh_state=state,
              only_load_props=attribute_names,
              no_autoflush=no_autoflush,
          )
  
      # if instance is pending, a refresh operation
      # may not complete (even if PK attributes are assigned)
      if has_key and result is None:
          raise orm_exc.ObjectDeletedError(state)
  