Edit: loading.py
# 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: 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 import collections 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 _SET_DEFERRED_EXPIRED from .util import _none_set from .util import state_str from .. import exc as sa_exc from .. import util from ..sql import util as sql_util _new_runid = util.counter() def instances(query, cursor, context): """Return an ORM result as an iterator.""" context.runid = _new_runid() context.post_load_paths = {} filtered = query._has_mapper_entities single_entity = query.is_single_entity if filtered: if single_entity: filter_fn = id else: def filter_fn(row): return tuple( id(item) if ent.use_id_for_hash else item for ent, item in zip(query._entities, row) ) try: (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 ] for path, post_load in context.post_load_paths.items(): post_load.invoke(context, path) if filtered: rows = util.unique_list(rows, filter_fn) for row in rows: yield row if not query._yield_per: break except Exception: with util.safe_reraise(): cursor.close() @util.dependencies("sqlalchemy.orm.query") def merge_result(querylib, query, iterator, load=True): """Merge a result into this :class:`_query.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={}, _resolve_conflict_map={}, ) 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={}, _resolve_conflict_map={}, ) result.append(keyed_tuple(newrow)) 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( query, key, refresh_state=None, with_for_update=None, only_load_props=None ): """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( query, ident, refresh_state=refresh_state, with_for_update=with_for_update, only_load_props=only_load_props, identity_token=identity_token, ) def load_on_pk_identity( query, primary_key_identity, refresh_state=None, with_for_update=None, only_load_props=None, identity_token=None, ): """Load the given primary key identity from the database.""" if refresh_state is None: q = query._clone() q._get_condition() else: q = query._clone() if primary_key_identity 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 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." ) _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( primary_key_identity, mapper.primary_key ) ] ) q._params = params # with_for_update needs to be query.LockmodeArg() 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 q._get_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 try: return q.one() except orm_exc.NoResultFound: return None def _setup_entity_query( context, 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(context.attributes, "memoized_setups", quick_populators) for value in poly_properties: if only_load_props and value.key not in only_load_props: continue value.setup( context, query_entity, path, adapter, only_load_props=only_load_props, column_collection=column_collection, memoized_populators=quick_populators, **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( 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. pk_cols = mapper.primary_key if adapter: pk_cols = [adapter.columns[c] for c in pk_cols] identity_class = mapper._identity_class populators = collections.defaultdict(list) 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 ) 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: 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. populators["expire"].append((prop.key, False)) else: getter = None # the "adapter" can be here via different paths, # e.g. via adapter present at setup_query or adapter # applied to the query afterwards via eager load subquery. # If the column here # were already a product of this adapter, sending it through # the adapter again can return a totally new expression that # won't be recognized in the result, and the ColumnAdapter # currently does not accommodate for this. OTOH, if the # column were never applied through this adapter, we may get # None back, in which case we still won't get our "getter". # so try both against result._getter(). See issue #4048 if adapter: 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: 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, path, mapper, result, adapter, populators ) else: prop.create_row_processor( context, path, mapper, result, adapter, populators ) propagate_options = context.propagate_options 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) 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 version_check = context.version_check runid = context.runid identity_token = context.identity_token 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 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, tuple([row[column] for column in pk_cols]), 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 not currentload: _validate_version_id(mapper, state, dict_, row, adapter) 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 (propagate_options or not populate_existing): state.load_options = propagate_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 _instance = _decorate_polymorphic_switch( _instance, context, mapper, result, path, polymorphic_discriminator, adapter, ) 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 orig_query._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, adapter): version_id_col = mapper.version_id_col if version_id_col is None: return if adapter: version_id_col = adapter.columns[version_id_col] if ( 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], ) ) def _decorate_polymorphic_switch( instance_fn, context, mapper, result, path, polymorphic_discriminator, adapter, ): 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 return _instance_processor( sub_mapper, context, result, path, adapter, _polymorphic_from=mapper, ) polymorphic_instances = util.PopulateDict(configure_subclass_mapper) def polymorphic_instance(row): discriminator = row[polymorphic_on] if discriminator is not None: _instance = polymorphic_instances[discriminator] if _instance: return _instance(row) return instance_fn(row) 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): """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 # 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: result = load_on_ident( session.query(mapper) .options(strategy_options.Load(mapper).undefer("*")) .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_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.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)
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