path: root/lib/sqlalchemy/orm/loading.py

# orm/loading.py
# Copyright (C) 2005-2014 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 .. import util
from . import attributes, exc as orm_exc
from ..sql import util as sql_util
from .util import _none_set, state_str
from .. import exc as sa_exc

_new_runid = util.counter()


def instances(query, cursor, context):
    """Return an ORM result as an iterator."""

    context.runid = _new_runid()

    filter_fns = [ent.filter_fn
                  for ent in query._entities]
    filtered = id in filter_fns

    single_entity = len(query._entities) == 1 and \
        query._entities[0].supports_single_entity

    if filtered:
        if single_entity:
            filter_fn = id
        else:
            def filter_fn(row):
                return tuple(fn(x) for x, fn in zip(row, filter_fns))

    (process, labels) = \
        list(zip(*[
            query_entity.row_processor(query,
                                       context, cursor)
            for query_entity in query._entities
        ]))

    if not single_entity:
        keyed_tuple = util.lightweight_named_tuple('result', labels)

    while True:
        context.partials = {}

        if query._yield_per:
            fetch = cursor.fetchmany(query._yield_per)
            if not fetch:
                break
        else:
            fetch = cursor.fetchall()

        if single_entity:
            proc = process[0]
            rows = [proc(row) for row in fetch]
        else:
            rows = [keyed_tuple([proc(row) for proc in process])
                    for row in fetch]

        if filtered:
            rows = util.unique_list(rows, filter_fn)

        for state, (dict_, attrs) in context.partials.items():
            state._commit(dict_, attrs)

        for row in rows:
            yield row

        if not query._yield_per:
            break


@util.dependencies("sqlalchemy.orm.query")
def merge_result(querylib, query, iterator, load=True):
    """Merge a result into this :class:`.Query` object's Session."""

    session = query.session
    if load:
        # flush current contents if we expect to load data
        session._autoflush()

    autoflush = session.autoflush
    try:
        session.autoflush = False
        single_entity = len(query._entities) == 1
        if single_entity:
            if isinstance(query._entities[0], querylib._MapperEntity):
                result = [session._merge(
                    attributes.instance_state(instance),
                    attributes.instance_dict(instance),
                    load=load, _recursive={})
                    for instance in iterator]
            else:
                result = list(iterator)
        else:
            mapped_entities = [i for i, e in enumerate(query._entities)
                               if isinstance(e, querylib._MapperEntity)]
            result = []
            keys = [ent._label_name for ent in query._entities]
            keyed_tuple = util.lightweight_named_tuple('result', keys)
            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={})
                result.append(keyed_tuple(newrow))

        return iter(result)
    finally:
        session.autoflush = autoflush


def get_from_identity(session, 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)

        # 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(state, passive)
            except orm_exc.ObjectDeletedError:
                session._remove_newly_deleted([state])
                return None
        return instance
    else:
        return None


def load_on_ident(query, key,
                  refresh_state=None, lockmode=None,
                  only_load_props=None):
    """Load the given identity key from the database."""

    if key is not None:
        ident = key[1]
    else:
        ident = None

    if refresh_state is None:
        q = query._clone()
        q._get_condition()
    else:
        q = query._clone()

    if ident is not None:
        mapper = query._mapper_zero()

        (_get_clause, _get_params) = mapper._get_clause

        # None present in ident - turn those comparisons
        # into "IS NULL"
        if None in ident:
            nones = set([
                        _get_params[col].key for col, value in
                        zip(mapper.primary_key, ident) if value is None
                        ])
            _get_clause = sql_util.adapt_criterion_to_null(
                _get_clause, nones)

        _get_clause = q._adapt_clause(_get_clause, True, False)
        q._criterion = _get_clause

        params = dict([
            (_get_params[primary_key].key, id_val)
            for id_val, primary_key in zip(ident, mapper.primary_key)
        ])

        q._params = params

    if lockmode is not None:
        version_check = True
        q = q.with_lockmode(lockmode)
    elif query._for_update_arg is not None:
        version_check = True
        q._for_update_arg = query._for_update_arg
    else:
        version_check = False

    q._get_options(
        populate_existing=bool(refresh_state),
        version_check=version_check,
        only_load_props=only_load_props,
        refresh_state=refresh_state)
    q._order_by = None

    try:
        return q.one()
    except orm_exc.NoResultFound:
        return None


def instance_processor(mapper, context, result, path, adapter,
                       polymorphic_from=None,
                       only_load_props=None,
                       refresh_state=None,
                       polymorphic_discriminator=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.

    pk_cols = mapper.primary_key

    if polymorphic_from or refresh_state:
        polymorphic_on = None
    else:
        if polymorphic_discriminator is not None:
            polymorphic_on = polymorphic_discriminator
        else:
            polymorphic_on = mapper.polymorphic_on
        if polymorphic_on is not None:
            polymorphic_instances = util.PopulateDict(
                _configure_subclass_mapper(
                    mapper,
                    context, result, path, adapter)
            )

    version_id_col = mapper.version_id_col

    if adapter:
        pk_cols = [adapter.columns[c] for c in pk_cols]
        if polymorphic_on is not None:
            polymorphic_on = adapter.columns[polymorphic_on]
        if version_id_col is not None:
            version_id_col = adapter.columns[version_id_col]

    identity_class = mapper._identity_class

    (new_populators, existing_populators,
        eager_populators) = _populators(
        mapper, context, path, result, adapter, only_load_props)

    load_path = context.query._current_path + path \
        if context.query._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)
    instance_state = attributes.instance_state
    instance_dict = attributes.instance_dict
    session_id = context.session.hash_key
    version_check = context.version_check
    runid = context.runid
    propagate_options = context.propagate_options

    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

    if mapper.allow_partial_pks:
        is_not_primary_key = _none_set.issuperset
    else:
        is_not_primary_key = _none_set.intersection

    def _instance(row):

        if polymorphic_on is not None:
            discriminator = row[polymorphic_on]
            if discriminator is not None:
                _instance = polymorphic_instances[discriminator]
                if _instance:
                    return _instance(row)

        # determine identity key
        identitykey = refresh_identity_key or (
            identity_class,
            tuple([row[column] for column in pk_cols])
        )

        instance = session_identity_map.get(identitykey)

        if instance is not None:
            state = instance_state(instance)
            dict_ = instance_dict(instance)

            isnew = state.runid != runid
            currentload = not isnew
            loaded_instance = False

            if version_check and not currentload and \
                    version_id_col is not None and \
                    mapper._get_state_attr_by_column(
                        state,
                        dict_,
                        mapper.version_id_col) != \
                    row[version_id_col]:

                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),
                       row[version_id_col]))
        elif refresh_state:
            # out of band refresh_state detected (i.e. its not in the
            # session.identity_map) honor it anyway.  this can happen
            # if a _get() occurs within save_obj(), such as
            # when eager_defaults is True.
            state = refresh_state
            instance = state.obj()
            dict_ = instance_dict(instance)
            isnew = state.runid != context.runid
            currentload = True
            loaded_instance = False
        else:
            # 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

            # attach instance to session.
            state.session_id = session_id
            session_identity_map._add_unpresent(state, identitykey)

        if currentload or populate_existing:
            # state is being fully loaded, so populate.
            # add to the "context.progress" collection.
            if isnew:
                state.runid = runid
                if propagate_options:
                    state.load_options = propagate_options
                if state.load_options:
                    state.load_path = load_path
                for key, populator in new_populators:
                    populator(state, dict_, row)
            else:
                for key, populator in existing_populators:
                    populator(state, dict_, row)

            if loaded_instance and load_evt:
                state.manager.dispatch.load(state, context)
            elif isnew and refresh_evt:
                state.manager.dispatch.refresh(
                    state, context, only_load_props)

            if populate_existing:
                if refresh_state and only_load_props:
                    state._commit(dict_, only_load_props)
                else:
                    state._commit_all(dict_, session_identity_map)

        elif state in context.partials or state.unloaded or eager_populators:
            # state is having a partial set of its attributes
            # refreshed.  Populate those attributes,
            # and add to the "context.partials" collection.
            unloaded = state.unloaded

            if state in context.partials:
                isnew = False
                (d_, attrs) = context.partials[state]
                for key, populator in existing_populators:
                    if key not in attrs:
                        continue
                    populator(state, dict_, row)
            else:
                isnew = True
                attrs = unloaded
                context.partials[state] = (dict_, attrs)
                if context.propagate_options:
                    state.load_options = context.propagate_options
                if state.load_options:
                    state.load_path = load_path
                for key, populator in new_populators:
                    if key not in attrs:
                        continue
                    populator(state, dict_, row)

            for key, pop in eager_populators:
                if key not in unloaded:
                    pop(state, dict_, row)

            if isnew and refresh_evt:
                state.manager.dispatch.refresh(state, context, attrs)

        return instance
    return _instance


def _populators(mapper, context, path, result, adapter, only_load_props):
    """Produce a collection of attribute level row processor
    callables."""

    new_populators = []
    existing_populators = []
    delayed_populators = []
    eager_populators = []
    invoke_eagers = context.invoke_all_eagers

    props = mapper._props.values()
    if only_load_props is not None:
        props = (p for p in props if p.key in only_load_props)

    for prop in props:
        np, ep, dp, gp = prop.create_row_processor(
            context, path, mapper, result, adapter)
        if np:
            new_populators.append((prop.key, np))
        if ep:
            existing_populators.append((prop.key, ep))
        if dp:
            delayed_populators.append((prop.key, dp))
        if invoke_eagers and gp:
            eager_populators.append((prop.key, gp))

    if delayed_populators:
        new_populators += delayed_populators

    return new_populators, existing_populators, eager_populators


def _configure_subclass_mapper(mapper, context, result, path, adapter):
    """Produce a mapper level row processor callable factory for mappers
    inheriting this one."""

    def configure_subclass_mapper(discriminator):
        try:
            sub_mapper = mapper.polymorphic_map[discriminator]
        except KeyError:
            raise AssertionError(
                "No such polymorphic_identity %r is defined" %
                discriminator)
        if sub_mapper is mapper:
            return None

        return instance_processor(
            sub_mapper,
            context,
            result,
            path,
            adapter,
            polymorphic_from=mapper)
    return configure_subclass_mapper


def load_scalar_attributes(mapper, state, attribute_names):
    """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

    if mapper.inherits and not mapper.concrete:
        statement = mapper._optimized_get_statement(state, attribute_names)
        if statement is not None:
            result = load_on_ident(
                session.query(mapper).from_statement(statement),
                None,
                only_load_props=attribute_names,
                refresh_state=state
            )

    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("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.query(mapper),
            identity_key,
            refresh_state=state,
            only_load_props=attribute_names)

    # 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)