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sqlalchemy
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orm
state.py
# orm/state.py # Copyright (C) 2005-2025 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 """Defines instrumentation of instances. This module is usually not directly visible to user applications, but defines a large part of the ORM's interactivity. """ from __future__ import annotations from typing import Any from typing import Callable from typing import Dict from typing import Generic from typing import Iterable from typing import Optional from typing import Set from typing import Tuple from typing import TYPE_CHECKING from typing import Union import weakref from . import base from . import exc as orm_exc from . import interfaces from ._typing import _O from ._typing import is_collection_impl from .base import ATTR_WAS_SET from .base import INIT_OK from .base import LoaderCallableStatus from .base import NEVER_SET from .base import NO_VALUE from .base import PASSIVE_NO_INITIALIZE from .base import PASSIVE_NO_RESULT from .base import PASSIVE_OFF from .base import SQL_OK from .path_registry import PathRegistry from .. import exc as sa_exc from .. import inspection from .. import util from ..util.typing import Literal from ..util.typing import Protocol if TYPE_CHECKING: from ._typing import _IdentityKeyType from ._typing import _InstanceDict from ._typing import _LoaderCallable from .attributes import AttributeImpl from .attributes import History from .base import PassiveFlag from .collections import _AdaptedCollectionProtocol from .identity import IdentityMap from .instrumentation import ClassManager from .interfaces import ORMOption from .mapper import Mapper from .session import Session from ..engine import Row from ..ext.asyncio.session import async_session as _async_provider from ..ext.asyncio.session import AsyncSession if TYPE_CHECKING: _sessions: weakref.WeakValueDictionary[int, Session] else: # late-populated by session.py _sessions = None if not TYPE_CHECKING: # optionally late-provided by sqlalchemy.ext.asyncio.session _async_provider = None # noqa class _InstanceDictProto(Protocol): def __call__(self) -> Optional[IdentityMap]: ... class _InstallLoaderCallableProto(Protocol[_O]): """used at result loading time to install a _LoaderCallable callable upon a specific InstanceState, which will be used to populate an attribute when that attribute is accessed. Concrete examples are per-instance deferred column loaders and relationship lazy loaders. """ def __call__( self, state: InstanceState[_O], dict_: _InstanceDict, row: Row[Any] ) -> None: ... @inspection._self_inspects class InstanceState(interfaces.InspectionAttrInfo, Generic[_O]): """Tracks state information at the instance level. The :class:`.InstanceState` is a key object used by the SQLAlchemy ORM in order to track the state of an object; it is created the moment an object is instantiated, typically as a result of :term:`instrumentation` which SQLAlchemy applies to the ``__init__()`` method of the class. :class:`.InstanceState` is also a semi-public object, available for runtime inspection as to the state of a mapped instance, including information such as its current status within a particular :class:`.Session` and details about data on individual attributes. The public API in order to acquire a :class:`.InstanceState` object is to use the :func:`_sa.inspect` system:: >>> from sqlalchemy import inspect >>> insp = inspect(some_mapped_object) >>> insp.attrs.nickname.history History(added=['new nickname'], unchanged=(), deleted=['nickname']) .. seealso:: :ref:`orm_mapper_inspection_instancestate` """ __slots__ = ( "__dict__", "__weakref__", "class_", "manager", "obj", "committed_state", "expired_attributes", ) manager: ClassManager[_O] session_id: Optional[int] = None key: Optional[_IdentityKeyType[_O]] = None runid: Optional[int] = None load_options: Tuple[ORMOption, ...] = () load_path: PathRegistry = PathRegistry.root insert_order: Optional[int] = None _strong_obj: Optional[object] = None obj: weakref.ref[_O] committed_state: Dict[str, Any] modified: bool = False """When ``True`` the object was modified.""" expired: bool = False """When ``True`` the object is :term:`expired`. .. seealso:: :ref:`session_expire` """ _deleted: bool = False _load_pending: bool = False _orphaned_outside_of_session: bool = False is_instance: bool = True identity_token: object = None _last_known_values: Optional[Dict[str, Any]] = None _instance_dict: _InstanceDictProto """A weak reference, or in the default case a plain callable, that returns a reference to the current :class:`.IdentityMap`, if any. """ if not TYPE_CHECKING: def _instance_dict(self): """default 'weak reference' for _instance_dict""" return None expired_attributes: Set[str] """The set of keys which are 'expired' to be loaded by the manager's deferred scalar loader, assuming no pending changes. See also the ``unmodified`` collection which is intersected against this set when a refresh operation occurs. """ callables: Dict[str, Callable[[InstanceState[_O], PassiveFlag], Any]] """A namespace where a per-state loader callable can be associated. In SQLAlchemy 1.0, this is only used for lazy loaders / deferred loaders that were set up via query option. Previously, callables was used also to indicate expired attributes by storing a link to the InstanceState itself in this dictionary. This role is now handled by the expired_attributes set. """ if not TYPE_CHECKING: callables = util.EMPTY_DICT def __init__(self, obj: _O, manager: ClassManager[_O]): self.class_ = obj.__class__ self.manager = manager self.obj = weakref.ref(obj, self._cleanup) self.committed_state = {} self.expired_attributes = set() @util.memoized_property def attrs(self) -> util.ReadOnlyProperties[AttributeState]: """Return a namespace representing each attribute on the mapped object, including its current value and history. The returned object is an instance of :class:`.AttributeState`. This object allows inspection of the current data within an attribute as well as attribute history since the last flush. """ return util.ReadOnlyProperties( {key: AttributeState(self, key) for key in self.manager} ) @property def transient(self) -> bool: """Return ``True`` if the object is :term:`transient`. .. seealso:: :ref:`session_object_states` """ return self.key is None and not self._attached @property def pending(self) -> bool: """Return ``True`` if the object is :term:`pending`. .. seealso:: :ref:`session_object_states` """ return self.key is None and self._attached @property def deleted(self) -> bool: """Return ``True`` if the object is :term:`deleted`. An object that is in the deleted state is guaranteed to not be within the :attr:`.Session.identity_map` of its parent :class:`.Session`; however if the session's transaction is rolled back, the object will be restored to the persistent state and the identity map. .. note:: The :attr:`.InstanceState.deleted` attribute refers to a specific state of the object that occurs between the "persistent" and "detached" states; once the object is :term:`detached`, the :attr:`.InstanceState.deleted` attribute **no longer returns True**; in order to detect that a state was deleted, regardless of whether or not the object is associated with a :class:`.Session`, use the :attr:`.InstanceState.was_deleted` accessor. .. versionadded: 1.1 .. seealso:: :ref:`session_object_states` """ return self.key is not None and self._attached and self._deleted @property def was_deleted(self) -> bool: """Return True if this object is or was previously in the "deleted" state and has not been reverted to persistent. This flag returns True once the object was deleted in flush. When the object is expunged from the session either explicitly or via transaction commit and enters the "detached" state, this flag will continue to report True. .. seealso:: :attr:`.InstanceState.deleted` - refers to the "deleted" state :func:`.orm.util.was_deleted` - standalone function :ref:`session_object_states` """ return self._deleted @property def persistent(self) -> bool: """Return ``True`` if the object is :term:`persistent`. An object that is in the persistent state is guaranteed to be within the :attr:`.Session.identity_map` of its parent :class:`.Session`. .. seealso:: :ref:`session_object_states` """ return self.key is not None and self._attached and not self._deleted @property def detached(self) -> bool: """Return ``True`` if the object is :term:`detached`. .. seealso:: :ref:`session_object_states` """ return self.key is not None and not self._attached @util.non_memoized_property @util.preload_module("sqlalchemy.orm.session") def _attached(self) -> bool: return ( self.session_id is not None and self.session_id in util.preloaded.orm_session._sessions ) def _track_last_known_value(self, key: str) -> None: """Track the last known value of a particular key after expiration operations. .. versionadded:: 1.3 """ lkv = self._last_known_values if lkv is None: self._last_known_values = lkv = {} if key not in lkv: lkv[key] = NO_VALUE @property def session(self) -> Optional[Session]: """Return the owning :class:`.Session` for this instance, or ``None`` if none available. Note that the result here can in some cases be *different* from that of ``obj in session``; an object that's been deleted will report as not ``in session``, however if the transaction is still in progress, this attribute will still refer to that session. Only when the transaction is completed does the object become fully detached under normal circumstances. .. seealso:: :attr:`_orm.InstanceState.async_session` """ if self.session_id: try: return _sessions[self.session_id] except KeyError: pass return None @property def async_session(self) -> Optional[AsyncSession]: """Return the owning :class:`_asyncio.AsyncSession` for this instance, or ``None`` if none available. This attribute is only non-None when the :mod:`sqlalchemy.ext.asyncio` API is in use for this ORM object. The returned :class:`_asyncio.AsyncSession` object will be a proxy for the :class:`_orm.Session` object that would be returned from the :attr:`_orm.InstanceState.session` attribute for this :class:`_orm.InstanceState`. .. versionadded:: 1.4.18 .. seealso:: :ref:`asyncio_toplevel` """ if _async_provider is None: return None sess = self.session if sess is not None: return _async_provider(sess) else: return None @property def object(self) -> Optional[_O]: """Return the mapped object represented by this :class:`.InstanceState`. Returns None if the object has been garbage collected """ return self.obj() @property def identity(self) -> Optional[Tuple[Any, ...]]: """Return the mapped identity of the mapped object. This is the primary key identity as persisted by the ORM which can always be passed directly to :meth:`_query.Query.get`. Returns ``None`` if the object has no primary key identity. .. note:: An object which is :term:`transient` or :term:`pending` does **not** have a mapped identity until it is flushed, even if its attributes include primary key values. """ if self.key is None: return None else: return self.key[1] @property def identity_key(self) -> Optional[_IdentityKeyType[_O]]: """Return the identity key for the mapped object. This is the key used to locate the object within the :attr:`.Session.identity_map` mapping. It contains the identity as returned by :attr:`.identity` within it. """ return self.key @util.memoized_property def parents(self) -> Dict[int, Union[Literal[False], InstanceState[Any]]]: return {} @util.memoized_property def _pending_mutations(self) -> Dict[str, PendingCollection]: return {} @util.memoized_property def _empty_collections(self) -> Dict[str, _AdaptedCollectionProtocol]: return {} @util.memoized_property def mapper(self) -> Mapper[_O]: """Return the :class:`_orm.Mapper` used for this mapped object.""" return self.manager.mapper @property def has_identity(self) -> bool: """Return ``True`` if this object has an identity key. This should always have the same value as the expression ``state.persistent`` or ``state.detached``. """ return bool(self.key) @classmethod def _detach_states( self, states: Iterable[InstanceState[_O]], session: Session, to_transient: bool = False, ) -> None: persistent_to_detached = ( session.dispatch.persistent_to_detached or None ) deleted_to_detached = session.dispatch.deleted_to_detached or None pending_to_transient = session.dispatch.pending_to_transient or None persistent_to_transient = ( session.dispatch.persistent_to_transient or None ) for state in states: deleted = state._deleted pending = state.key is None persistent = not pending and not deleted state.session_id = None if to_transient and state.key: del state.key if persistent: if to_transient: if persistent_to_transient is not None: persistent_to_transient(session, state) elif persistent_to_detached is not None: persistent_to_detached(session, state) elif deleted and deleted_to_detached is not None: deleted_to_detached(session, state) elif pending and pending_to_transient is not None: pending_to_transient(session, state) state._strong_obj = None def _detach(self, session: Optional[Session] = None) -> None: if session: InstanceState._detach_states([self], session) else: self.session_id = self._strong_obj = None def _dispose(self) -> None: # used by the test suite, apparently self._detach() def _cleanup(self, ref: weakref.ref[_O]) -> None: """Weakref callback cleanup. This callable cleans out the state when it is being garbage collected. this _cleanup **assumes** that there are no strong refs to us! Will not work otherwise! """ # Python builtins become undefined during interpreter shutdown. # Guard against exceptions during this phase, as the method cannot # proceed in any case if builtins have been undefined. if dict is None: return instance_dict = self._instance_dict() if instance_dict is not None: instance_dict._fast_discard(self) del self._instance_dict # we can't possibly be in instance_dict._modified # b.c. this is weakref cleanup only, that set # is strong referencing! # assert self not in instance_dict._modified self.session_id = self._strong_obj = None @property def dict(self) -> _InstanceDict: """Return the instance dict used by the object. Under normal circumstances, this is always synonymous with the ``__dict__`` attribute of the mapped object, unless an alternative instrumentation system has been configured. In the case that the actual object has been garbage collected, this accessor returns a blank dictionary. """ o = self.obj() if o is not None: return base.instance_dict(o) else: return {} def _initialize_instance(*mixed: Any, **kwargs: Any) -> None: self, instance, args = mixed[0], mixed[1], mixed[2:] # noqa manager = self.manager manager.dispatch.init(self, args, kwargs) try: manager.original_init(*mixed[1:], **kwargs) except: with util.safe_reraise(): manager.dispatch.init_failure(self, args, kwargs) def get_history(self, key: str, passive: PassiveFlag) -> History: return self.manager[key].impl.get_history(self, self.dict, passive) def get_impl(self, key: str) -> AttributeImpl: return self.manager[key].impl def _get_pending_mutation(self, key: str) -> PendingCollection: if key not in self._pending_mutations: self._pending_mutations[key] = PendingCollection() return self._pending_mutations[key] def __getstate__(self) -> Dict[str, Any]: state_dict: Dict[str, Any] = { "instance": self.obj(), "class_": self.class_, "committed_state": self.committed_state, "expired_attributes": self.expired_attributes, } state_dict.update( (k, self.__dict__[k]) for k in ( "_pending_mutations", "modified", "expired", "callables", "key", "parents", "load_options", "class_", "expired_attributes", "info", ) if k in self.__dict__ ) if self.load_path: state_dict["load_path"] = self.load_path.serialize() state_dict["manager"] = self.manager._serialize(self, state_dict) return state_dict def __setstate__(self, state_dict: Dict[str, Any]) -> None: inst = state_dict["instance"] if inst is not None: self.obj = weakref.ref(inst, self._cleanup) self.class_ = inst.__class__ else: self.obj = lambda: None # type: ignore self.class_ = state_dict["class_"] self.committed_state = state_dict.get("committed_state", {}) self._pending_mutations = state_dict.get("_pending_mutations", {}) self.parents = state_dict.get("parents", {}) self.modified = state_dict.get("modified", False) self.expired = state_dict.get("expired", False) if "info" in state_dict: self.info.update(state_dict["info"]) if "callables" in state_dict: self.callables = state_dict["callables"] self.expired_attributes = state_dict["expired_attributes"] else: if "expired_attributes" in state_dict: self.expired_attributes = state_dict["expired_attributes"] else: self.expired_attributes = set() self.__dict__.update( [ (k, state_dict[k]) for k in ("key", "load_options") if k in state_dict ] ) if self.key: self.identity_token = self.key[2] if "load_path" in state_dict: self.load_path = PathRegistry.deserialize(state_dict["load_path"]) state_dict["manager"](self, inst, state_dict) def _reset(self, dict_: _InstanceDict, key: str) -> None: """Remove the given attribute and any callables associated with it.""" old = dict_.pop(key, None) manager_impl = self.manager[key].impl if old is not None and is_collection_impl(manager_impl): manager_impl._invalidate_collection(old) self.expired_attributes.discard(key) if self.callables: self.callables.pop(key, None) def _copy_callables(self, from_: InstanceState[Any]) -> None: if "callables" in from_.__dict__: self.callables = dict(from_.callables) @classmethod def _instance_level_callable_processor( cls, manager: ClassManager[_O], fn: _LoaderCallable, key: Any ) -> _InstallLoaderCallableProto[_O]: impl = manager[key].impl if is_collection_impl(impl): fixed_impl = impl def _set_callable( state: InstanceState[_O], dict_: _InstanceDict, row: Row[Any] ) -> None: if "callables" not in state.__dict__: state.callables = {} old = dict_.pop(key, None) if old is not None: fixed_impl._invalidate_collection(old) state.callables[key] = fn else: def _set_callable( state: InstanceState[_O], dict_: _InstanceDict, row: Row[Any] ) -> None: if "callables" not in state.__dict__: state.callables = {} state.callables[key] = fn return _set_callable def _expire( self, dict_: _InstanceDict, modified_set: Set[InstanceState[Any]] ) -> None: self.expired = True if self.modified: modified_set.discard(self) self.committed_state.clear() self.modified = False self._strong_obj = None if "_pending_mutations" in self.__dict__: del self.__dict__["_pending_mutations"] if "parents" in self.__dict__: del self.__dict__["parents"] self.expired_attributes.update( [impl.key for impl in self.manager._loader_impls] ) if self.callables: # the per state loader callables we can remove here are # LoadDeferredColumns, which undefers a column at the instance # level that is mapped with deferred, and LoadLazyAttribute, # which lazy loads a relationship at the instance level that # is mapped with "noload" or perhaps "immediateload". # Before 1.4, only column-based # attributes could be considered to be "expired", so here they # were the only ones "unexpired", which means to make them deferred # again. For the moment, as of 1.4 we also apply the same # treatment relationships now, that is, an instance level lazy # loader is reset in the same way as a column loader. for k in self.expired_attributes.intersection(self.callables): del self.callables[k] for k in self.manager._collection_impl_keys.intersection(dict_): collection = dict_.pop(k) collection._sa_adapter.invalidated = True if self._last_known_values: self._last_known_values.update( {k: dict_[k] for k in self._last_known_values if k in dict_} ) for key in self.manager._all_key_set.intersection(dict_): del dict_[key] self.manager.dispatch.expire(self, None) def _expire_attributes( self, dict_: _InstanceDict, attribute_names: Iterable[str], no_loader: bool = False, ) -> None: pending = self.__dict__.get("_pending_mutations", None) callables = self.callables for key in attribute_names: impl = self.manager[key].impl if impl.accepts_scalar_loader: if no_loader and (impl.callable_ or key in callables): continue self.expired_attributes.add(key) if callables and key in callables: del callables[key] old = dict_.pop(key, NO_VALUE) if is_collection_impl(impl) and old is not NO_VALUE: impl._invalidate_collection(old) lkv = self._last_known_values if lkv is not None and key in lkv and old is not NO_VALUE: lkv[key] = old self.committed_state.pop(key, None) if pending: pending.pop(key, None) self.manager.dispatch.expire(self, attribute_names) def _load_expired( self, state: InstanceState[_O], passive: PassiveFlag ) -> LoaderCallableStatus: """__call__ allows the InstanceState to act as a deferred callable for loading expired attributes, which is also serializable (picklable). """ if not passive & SQL_OK: return PASSIVE_NO_RESULT toload = self.expired_attributes.intersection(self.unmodified) toload = toload.difference( attr for attr in toload if not self.manager[attr].impl.load_on_unexpire ) self.manager.expired_attribute_loader(self, toload, passive) # if the loader failed, or this # instance state didn't have an identity, # the attributes still might be in the callables # dict. ensure they are removed. self.expired_attributes.clear() return ATTR_WAS_SET @property def unmodified(self) -> Set[str]: """Return the set of keys which have no uncommitted changes""" return set(self.manager).difference(self.committed_state) def unmodified_intersection(self, keys: Iterable[str]) -> Set[str]: """Return self.unmodified.intersection(keys).""" return ( set(keys) .intersection(self.manager) .difference(self.committed_state) ) @property def unloaded(self) -> Set[str]: """Return the set of keys which do not have a loaded value. This includes expired attributes and any other attribute that was never populated or modified. """ return ( set(self.manager) .difference(self.committed_state) .difference(self.dict) ) @property @util.deprecated( "2.0", "The :attr:`.InstanceState.unloaded_expirable` attribute is " "deprecated. Please use :attr:`.InstanceState.unloaded`.", ) def unloaded_expirable(self) -> Set[str]: """Synonymous with :attr:`.InstanceState.unloaded`. This attribute was added as an implementation-specific detail at some point and should be considered to be private. """ return self.unloaded @property def _unloaded_non_object(self) -> Set[str]: return self.unloaded.intersection( attr for attr in self.manager if self.manager[attr].impl.accepts_scalar_loader ) def _modified_event( self, dict_: _InstanceDict, attr: Optional[AttributeImpl], previous: Any, collection: bool = False, is_userland: bool = False, ) -> None: if attr: if not attr.send_modified_events: return if is_userland and attr.key not in dict_: raise sa_exc.InvalidRequestError( "Can't flag attribute '%s' modified; it's not present in " "the object state" % attr.key ) if attr.key not in self.committed_state or is_userland: if collection: if TYPE_CHECKING: assert is_collection_impl(attr) if previous is NEVER_SET: if attr.key in dict_: previous = dict_[attr.key] if previous not in (None, NO_VALUE, NEVER_SET): previous = attr.copy(previous) self.committed_state[attr.key] = previous lkv = self._last_known_values if lkv is not None and attr.key in lkv: lkv[attr.key] = NO_VALUE # assert self._strong_obj is None or self.modified if (self.session_id and self._strong_obj is None) or not self.modified: self.modified = True instance_dict = self._instance_dict() if instance_dict: has_modified = bool(instance_dict._modified) instance_dict._modified.add(self) else: has_modified = False # only create _strong_obj link if attached # to a session inst = self.obj() if self.session_id: self._strong_obj = inst # if identity map already had modified objects, # assume autobegin already occurred, else check # for autobegin if not has_modified: # inline of autobegin, to ensure session transaction # snapshot is established try: session = _sessions[self.session_id] except KeyError: pass else: if session._transaction is None: session._autobegin_t() if inst is None and attr: raise orm_exc.ObjectDereferencedError( "Can't emit change event for attribute '%s' - " "parent object of type %s has been garbage " "collected." % (self.manager[attr.key], base.state_class_str(self)) ) def _commit(self, dict_: _InstanceDict, keys: Iterable[str]) -> None: """Commit attributes. This is used by a partial-attribute load operation to mark committed those attributes which were refreshed from the database. Attributes marked as "expired" can potentially remain "expired" after this step if a value was not populated in state.dict. """ for key in keys: self.committed_state.pop(key, None) self.expired = False self.expired_attributes.difference_update( set(keys).intersection(dict_) ) # the per-keys commit removes object-level callables, # while that of commit_all does not. it's not clear # if this behavior has a clear rationale, however tests do # ensure this is what it does. if self.callables: for key in ( set(self.callables).intersection(keys).intersection(dict_) ): del self.callables[key] def _commit_all( self, dict_: _InstanceDict, instance_dict: Optional[IdentityMap] = None ) -> None: """commit all attributes unconditionally. This is used after a flush() or a full load/refresh to remove all pending state from the instance. - all attributes are marked as "committed" - the "strong dirty reference" is removed - the "modified" flag is set to False - any "expired" markers for scalar attributes loaded are removed. - lazy load callables for objects / collections *stay* Attributes marked as "expired" can potentially remain "expired" after this step if a value was not populated in state.dict. """ self._commit_all_states([(self, dict_)], instance_dict) @classmethod def _commit_all_states( self, iter_: Iterable[Tuple[InstanceState[Any], _InstanceDict]], instance_dict: Optional[IdentityMap] = None, ) -> None: """Mass / highly inlined version of commit_all().""" for state, dict_ in iter_: state_dict = state.__dict__ state.committed_state.clear() if "_pending_mutations" in state_dict: del state_dict["_pending_mutations"] state.expired_attributes.difference_update(dict_) if instance_dict and state.modified: instance_dict._modified.discard(state) state.modified = state.expired = False state._strong_obj = None class AttributeState: """Provide an inspection interface corresponding to a particular attribute on a particular mapped object. The :class:`.AttributeState` object is accessed via the :attr:`.InstanceState.attrs` collection of a particular :class:`.InstanceState`:: from sqlalchemy import inspect insp = inspect(some_mapped_object) attr_state = insp.attrs.some_attribute """ __slots__ = ("state", "key") state: InstanceState[Any] key: str def __init__(self, state: InstanceState[Any], key: str): self.state = state self.key = key @property def loaded_value(self) -> Any: """The current value of this attribute as loaded from the database. If the value has not been loaded, or is otherwise not present in the object's dictionary, returns NO_VALUE. """ return self.state.dict.get(self.key, NO_VALUE) @property def value(self) -> Any: """Return the value of this attribute. This operation is equivalent to accessing the object's attribute directly or via ``getattr()``, and will fire off any pending loader callables if needed. """ return self.state.manager[self.key].__get__( self.state.obj(), self.state.class_ ) @property def history(self) -> History: """Return the current **pre-flush** change history for this attribute, via the :class:`.History` interface. This method will **not** emit loader callables if the value of the attribute is unloaded. .. note:: The attribute history system tracks changes on a **per flush basis**. Each time the :class:`.Session` is flushed, the history of each attribute is reset to empty. The :class:`.Session` by default autoflushes each time a :class:`_query.Query` is invoked. For options on how to control this, see :ref:`session_flushing`. .. seealso:: :meth:`.AttributeState.load_history` - retrieve history using loader callables if the value is not locally present. :func:`.attributes.get_history` - underlying function """ return self.state.get_history(self.key, PASSIVE_NO_INITIALIZE) def load_history(self) -> History: """Return the current **pre-flush** change history for this attribute, via the :class:`.History` interface. This method **will** emit loader callables if the value of the attribute is unloaded. .. note:: The attribute history system tracks changes on a **per flush basis**. Each time the :class:`.Session` is flushed, the history of each attribute is reset to empty. The :class:`.Session` by default autoflushes each time a :class:`_query.Query` is invoked. For options on how to control this, see :ref:`session_flushing`. .. seealso:: :attr:`.AttributeState.history` :func:`.attributes.get_history` - underlying function """ return self.state.get_history(self.key, PASSIVE_OFF ^ INIT_OK) class PendingCollection: """A writable placeholder for an unloaded collection. Stores items appended to and removed from a collection that has not yet been loaded. When the collection is loaded, the changes stored in PendingCollection are applied to it to produce the final result. """ __slots__ = ("deleted_items", "added_items") deleted_items: util.IdentitySet added_items: util.OrderedIdentitySet def __init__(self) -> None: self.deleted_items = util.IdentitySet() self.added_items = util.OrderedIdentitySet() def merge_with_history(self, history: History) -> History: return history._merge(self.added_items, self.deleted_items) def append(self, value: Any) -> None: if value in self.deleted_items: self.deleted_items.remove(value) else: self.added_items.add(value) def remove(self, value: Any) -> None: if value in self.added_items: self.added_items.remove(value) else: self.deleted_items.add(value)
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