# orm/loading.py
# Copyright (C) 2005-2021 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: https://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
from ..sql.selectable import LABEL_STYLE_TABLENAME_PLUS_COL

_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()

    def _no_unique(entry):
        raise sa_exc.InvalidRequestError(
            "Can't use the ORM yield_per feature in conjunction with unique()"
        )

    def _not_hashable(datatype):
        def go(obj):
            raise sa_exc.InvalidRequestError(
                "Can't apply uniqueness to row tuple containing value of "
                "type %r; this datatype produces non-hashable values"
                % datatype
            )

        return go

    if context.load_options._legacy_uniquing:
        unique_filters = [
            _no_unique
            if context.yield_per
            else id
            if (
                ent.use_id_for_hash
                or ent._non_hashable_value
                or ent._null_column_type
            )
            else None
            for ent in context.compile_state._entities
        ]
    else:
        unique_filters = [
            _no_unique
            if context.yield_per
            else _not_hashable(ent.column.type)
            if (not ent.use_id_for_hash and ent._non_hashable_value)
            else id
            if ent.use_id_for_hash
            else None
            for ent in context.compile_state._entities
        ]

    row_metadata = SimpleResultMetaData(
        labels, extra, _unique_filters=unique_filters
    )

    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

    if context.execution_options.get("prebuffer_rows", False):
        # this is a bit of a hack at the moment.
        # I would rather have some option in the result to pre-buffer
        # internally.
        _prebuffered = list(chunks(None))

        def chunks(size):
            return iter(_prebuffered)

    result = ChunkedIteratorResult(
        row_metadata,
        chunks,
        source_supports_scalars=single_entity,
        raw=cursor,
        dynamic_yield_per=cursor.context._is_server_side,
    )

    # filtered and single_entity are used to indicate to legacy Query that the
    # query has ORM entities, so legacy deduping and scalars should be called
    # on the result.
    result._attributes = result._attributes.union(
        dict(filtered=filtered, is_single_entity=single_entity)
    )

    # multi_row_eager_loaders OTOH is specific to joinedload.
    if context.compile_state.multi_row_eager_loaders:

        def require_unique(obj):
            raise sa_exc.InvalidRequestError(
                "The unique() method must be invoked on this Result, "
                "as it contains results that include joined eager loads "
                "against collections"
            )

        result._unique_filter_state = (None, require_unique)

    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, legacy=False
    )

    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, legacy=True
    )

    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.
                # also used by immediateloader for a mutually-dependent
                # o2m->m2m load, :ticket:`6301`
                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})
                ),
                # this track_on will allow the lambda to refresh if
                # _get_clause goes stale due to reconfigured mapper.
                # however, it's not needed as the lambda otherwise tracks
                # on the SQL cache key of the expression.  the main thing
                # is that the bindparam.key stays the same if the cache key
                # stays the same, as we are referring to the .key explicitly
                # in the params.
                # track_on=[id(_get_clause)]
            )
        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,
            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,
            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,
        )
        .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 adapter:
                        # this logic had been removed for all 1.4 releases
                        # up until 1.4.18; the adapter here is particularly
                        # the compound eager adapter which isn't accommodated
                        # in the quick_populators right now.  The "fallback"
                        # logic below instead took over in many more cases
                        # until issue #6596 was identified.

                        # note there is still an issue where this codepath
                        # produces no "getter" for cases where a joined-inh
                        # mapping includes a labeled column property, meaning
                        # KeyError is caught internally and we fall back to
                        # _getter(col), which works anyway.   The adapter
                        # here for joined inh without any aliasing might not
                        # be useful.  Tests which see this include
                        # test.orm.inheritance.test_basic ->
                        # EagerTargetingTest.test_adapt_stringency
                        # OptimizedLoadTest.test_column_expression_joined
                        # PolymorphicOnNotLocalTest.test_polymorphic_on_column_prop  # noqa E501
                        #

                        adapted_col = adapter.columns[col]
                        if adapted_col is not None:
                            getter = result._getter(adapted_col, False)
                    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)

        effective_populate_existing = populate_existing
        if refresh_state is state:
            effective_populate_existing = True

        # 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 effective_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 effective_populate_existing
            ):
                state.load_options = propagated_loader_options
                state.load_path = load_path

            _populate_full(
                context,
                row,
                state,
                dict_,
                isnew,
                load_path,
                loaded_instance,
                effective_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 effective_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) or state.session.autocommit
    )

    # 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, don't 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).set_label_style(
                LABEL_STYLE_TABLENAME_PLUS_COL
            ),
            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)
