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unitofwork.py
# orm/unitofwork.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 # mypy: ignore-errors """The internals for the unit of work system. The session's flush() process passes objects to a contextual object here, which assembles flush tasks based on mappers and their properties, organizes them in order of dependency, and executes. """ from __future__ import annotations from typing import Any from typing import Dict from typing import Optional from typing import Set from typing import TYPE_CHECKING from . import attributes from . import exc as orm_exc from . import util as orm_util from .. import event from .. import util from ..util import topological if TYPE_CHECKING: from .dependency import DependencyProcessor from .interfaces import MapperProperty from .mapper import Mapper from .session import Session from .session import SessionTransaction from .state import InstanceState def track_cascade_events(descriptor, prop): """Establish event listeners on object attributes which handle cascade-on-set/append. """ key = prop.key def append(state, item, initiator, **kw): # process "save_update" cascade rules for when # an instance is appended to the list of another instance if item is None: return sess = state.session if sess: if sess._warn_on_events: sess._flush_warning("collection append") prop = state.manager.mapper._props[key] item_state = attributes.instance_state(item) if ( prop._cascade.save_update and (key == initiator.key) and not sess._contains_state(item_state) ): sess._save_or_update_state(item_state) return item def remove(state, item, initiator, **kw): if item is None: return sess = state.session prop = state.manager.mapper._props[key] if sess and sess._warn_on_events: sess._flush_warning( "collection remove" if prop.uselist else "related attribute delete" ) if ( item is not None and item is not attributes.NEVER_SET and item is not attributes.PASSIVE_NO_RESULT and prop._cascade.delete_orphan ): # expunge pending orphans item_state = attributes.instance_state(item) if prop.mapper._is_orphan(item_state): if sess and item_state in sess._new: sess.expunge(item) else: # the related item may or may not itself be in a # Session, however the parent for which we are catching # the event is not in a session, so memoize this on the # item item_state._orphaned_outside_of_session = True def set_(state, newvalue, oldvalue, initiator, **kw): # process "save_update" cascade rules for when an instance # is attached to another instance if oldvalue is newvalue: return newvalue sess = state.session if sess: if sess._warn_on_events: sess._flush_warning("related attribute set") prop = state.manager.mapper._props[key] if newvalue is not None: newvalue_state = attributes.instance_state(newvalue) if ( prop._cascade.save_update and (key == initiator.key) and not sess._contains_state(newvalue_state) ): sess._save_or_update_state(newvalue_state) if ( oldvalue is not None and oldvalue is not attributes.NEVER_SET and oldvalue is not attributes.PASSIVE_NO_RESULT and prop._cascade.delete_orphan ): # possible to reach here with attributes.NEVER_SET ? oldvalue_state = attributes.instance_state(oldvalue) if oldvalue_state in sess._new and prop.mapper._is_orphan( oldvalue_state ): sess.expunge(oldvalue) return newvalue event.listen( descriptor, "append_wo_mutation", append, raw=True, include_key=True ) event.listen( descriptor, "append", append, raw=True, retval=True, include_key=True ) event.listen( descriptor, "remove", remove, raw=True, retval=True, include_key=True ) event.listen( descriptor, "set", set_, raw=True, retval=True, include_key=True ) class UOWTransaction: session: Session transaction: SessionTransaction attributes: Dict[str, Any] deps: util.defaultdict[Mapper[Any], Set[DependencyProcessor]] mappers: util.defaultdict[Mapper[Any], Set[InstanceState[Any]]] def __init__(self, session: Session): self.session = session # dictionary used by external actors to # store arbitrary state information. self.attributes = {} # dictionary of mappers to sets of # DependencyProcessors, which are also # set to be part of the sorted flush actions, # which have that mapper as a parent. self.deps = util.defaultdict(set) # dictionary of mappers to sets of InstanceState # items pending for flush which have that mapper # as a parent. self.mappers = util.defaultdict(set) # a dictionary of Preprocess objects, which gather # additional states impacted by the flush # and determine if a flush action is needed self.presort_actions = {} # dictionary of PostSortRec objects, each # one issues work during the flush within # a certain ordering. self.postsort_actions = {} # a set of 2-tuples, each containing two # PostSortRec objects where the second # is dependent on the first being executed # first self.dependencies = set() # dictionary of InstanceState-> (isdelete, listonly) # tuples, indicating if this state is to be deleted # or insert/updated, or just refreshed self.states = {} # tracks InstanceStates which will be receiving # a "post update" call. Keys are mappers, # values are a set of states and a set of the # columns which should be included in the update. self.post_update_states = util.defaultdict(lambda: (set(), set())) @property def has_work(self): return bool(self.states) def was_already_deleted(self, state): """Return ``True`` if the given state is expired and was deleted previously. """ if state.expired: try: state._load_expired(state, attributes.PASSIVE_OFF) except orm_exc.ObjectDeletedError: self.session._remove_newly_deleted([state]) return True return False def is_deleted(self, state): """Return ``True`` if the given state is marked as deleted within this uowtransaction.""" return state in self.states and self.states[state][0] def memo(self, key, callable_): if key in self.attributes: return self.attributes[key] else: self.attributes[key] = ret = callable_() return ret def remove_state_actions(self, state): """Remove pending actions for a state from the uowtransaction.""" isdelete = self.states[state][0] self.states[state] = (isdelete, True) def get_attribute_history( self, state, key, passive=attributes.PASSIVE_NO_INITIALIZE ): """Facade to attributes.get_state_history(), including caching of results.""" hashkey = ("history", state, key) # cache the objects, not the states; the strong reference here # prevents newly loaded objects from being dereferenced during the # flush process if hashkey in self.attributes: history, state_history, cached_passive = self.attributes[hashkey] # if the cached lookup was "passive" and now # we want non-passive, do a non-passive lookup and re-cache if ( not cached_passive & attributes.SQL_OK and passive & attributes.SQL_OK ): impl = state.manager[key].impl history = impl.get_history( state, state.dict, attributes.PASSIVE_OFF | attributes.LOAD_AGAINST_COMMITTED | attributes.NO_RAISE, ) if history and impl.uses_objects: state_history = history.as_state() else: state_history = history self.attributes[hashkey] = (history, state_history, passive) else: impl = state.manager[key].impl # TODO: store the history as (state, object) tuples # so we don't have to keep converting here history = impl.get_history( state, state.dict, passive | attributes.LOAD_AGAINST_COMMITTED | attributes.NO_RAISE, ) if history and impl.uses_objects: state_history = history.as_state() else: state_history = history self.attributes[hashkey] = (history, state_history, passive) return state_history def has_dep(self, processor): return (processor, True) in self.presort_actions def register_preprocessor(self, processor, fromparent): key = (processor, fromparent) if key not in self.presort_actions: self.presort_actions[key] = Preprocess(processor, fromparent) def register_object( self, state: InstanceState[Any], isdelete: bool = False, listonly: bool = False, cancel_delete: bool = False, operation: Optional[str] = None, prop: Optional[MapperProperty] = None, ) -> bool: if not self.session._contains_state(state): # this condition is normal when objects are registered # as part of a relationship cascade operation. it should # not occur for the top-level register from Session.flush(). if not state.deleted and operation is not None: util.warn( "Object of type %s not in session, %s operation " "along '%s' will not proceed" % (orm_util.state_class_str(state), operation, prop) ) return False if state not in self.states: mapper = state.manager.mapper if mapper not in self.mappers: self._per_mapper_flush_actions(mapper) self.mappers[mapper].add(state) self.states[state] = (isdelete, listonly) else: if not listonly and (isdelete or cancel_delete): self.states[state] = (isdelete, False) return True def register_post_update(self, state, post_update_cols): mapper = state.manager.mapper.base_mapper states, cols = self.post_update_states[mapper] states.add(state) cols.update(post_update_cols) def _per_mapper_flush_actions(self, mapper): saves = SaveUpdateAll(self, mapper.base_mapper) deletes = DeleteAll(self, mapper.base_mapper) self.dependencies.add((saves, deletes)) for dep in mapper._dependency_processors: dep.per_property_preprocessors(self) for prop in mapper.relationships: if prop.viewonly: continue dep = prop._dependency_processor dep.per_property_preprocessors(self) @util.memoized_property def _mapper_for_dep(self): """return a dynamic mapping of (Mapper, DependencyProcessor) to True or False, indicating if the DependencyProcessor operates on objects of that Mapper. The result is stored in the dictionary persistently once calculated. """ return util.PopulateDict( lambda tup: tup[0]._props.get(tup[1].key) is tup[1].prop ) def filter_states_for_dep(self, dep, states): """Filter the given list of InstanceStates to those relevant to the given DependencyProcessor. """ mapper_for_dep = self._mapper_for_dep return [s for s in states if mapper_for_dep[(s.manager.mapper, dep)]] def states_for_mapper_hierarchy(self, mapper, isdelete, listonly): checktup = (isdelete, listonly) for mapper in mapper.base_mapper.self_and_descendants: for state in self.mappers[mapper]: if self.states[state] == checktup: yield state def _generate_actions(self): """Generate the full, unsorted collection of PostSortRecs as well as dependency pairs for this UOWTransaction. """ # execute presort_actions, until all states # have been processed. a presort_action might # add new states to the uow. while True: ret = False for action in list(self.presort_actions.values()): if action.execute(self): ret = True if not ret: break # see if the graph of mapper dependencies has cycles. self.cycles = cycles = topological.find_cycles( self.dependencies, list(self.postsort_actions.values()) ) if cycles: # if yes, break the per-mapper actions into # per-state actions convert = { rec: set(rec.per_state_flush_actions(self)) for rec in cycles } # rewrite the existing dependencies to point to # the per-state actions for those per-mapper actions # that were broken up. for edge in list(self.dependencies): if ( None in edge or edge[0].disabled or edge[1].disabled or cycles.issuperset(edge) ): self.dependencies.remove(edge) elif edge[0] in cycles: self.dependencies.remove(edge) for dep in convert[edge[0]]: self.dependencies.add((dep, edge[1])) elif edge[1] in cycles: self.dependencies.remove(edge) for dep in convert[edge[1]]: self.dependencies.add((edge[0], dep)) return { a for a in self.postsort_actions.values() if not a.disabled }.difference(cycles) def execute(self) -> None: postsort_actions = self._generate_actions() postsort_actions = sorted( postsort_actions, key=lambda item: item.sort_key, ) # sort = topological.sort(self.dependencies, postsort_actions) # print "--------------" # print "\ndependencies:", self.dependencies # print "\ncycles:", self.cycles # print "\nsort:", list(sort) # print "\nCOUNT OF POSTSORT ACTIONS", len(postsort_actions) # execute if self.cycles: for subset in topological.sort_as_subsets( self.dependencies, postsort_actions ): set_ = set(subset) while set_: n = set_.pop() n.execute_aggregate(self, set_) else: for rec in topological.sort(self.dependencies, postsort_actions): rec.execute(self) def finalize_flush_changes(self) -> None: """Mark processed objects as clean / deleted after a successful flush(). This method is called within the flush() method after the execute() method has succeeded and the transaction has been committed. """ if not self.states: return states = set(self.states) isdel = { s for (s, (isdelete, listonly)) in self.states.items() if isdelete } other = states.difference(isdel) if isdel: self.session._remove_newly_deleted(isdel) if other: self.session._register_persistent(other) class IterateMappersMixin: __slots__ = () def _mappers(self, uow): if self.fromparent: return iter( m for m in self.dependency_processor.parent.self_and_descendants if uow._mapper_for_dep[(m, self.dependency_processor)] ) else: return self.dependency_processor.mapper.self_and_descendants class Preprocess(IterateMappersMixin): __slots__ = ( "dependency_processor", "fromparent", "processed", "setup_flush_actions", ) def __init__(self, dependency_processor, fromparent): self.dependency_processor = dependency_processor self.fromparent = fromparent self.processed = set() self.setup_flush_actions = False def execute(self, uow): delete_states = set() save_states = set() for mapper in self._mappers(uow): for state in uow.mappers[mapper].difference(self.processed): (isdelete, listonly) = uow.states[state] if not listonly: if isdelete: delete_states.add(state) else: save_states.add(state) if delete_states: self.dependency_processor.presort_deletes(uow, delete_states) self.processed.update(delete_states) if save_states: self.dependency_processor.presort_saves(uow, save_states) self.processed.update(save_states) if delete_states or save_states: if not self.setup_flush_actions and ( self.dependency_processor.prop_has_changes( uow, delete_states, True ) or self.dependency_processor.prop_has_changes( uow, save_states, False ) ): self.dependency_processor.per_property_flush_actions(uow) self.setup_flush_actions = True return True else: return False class PostSortRec: __slots__ = ("disabled",) def __new__(cls, uow, *args): key = (cls,) + args if key in uow.postsort_actions: return uow.postsort_actions[key] else: uow.postsort_actions[key] = ret = object.__new__(cls) ret.disabled = False return ret def execute_aggregate(self, uow, recs): self.execute(uow) class ProcessAll(IterateMappersMixin, PostSortRec): __slots__ = "dependency_processor", "isdelete", "fromparent", "sort_key" def __init__(self, uow, dependency_processor, isdelete, fromparent): self.dependency_processor = dependency_processor self.sort_key = ( "ProcessAll", self.dependency_processor.sort_key, isdelete, ) self.isdelete = isdelete self.fromparent = fromparent uow.deps[dependency_processor.parent.base_mapper].add( dependency_processor ) def execute(self, uow): states = self._elements(uow) if self.isdelete: self.dependency_processor.process_deletes(uow, states) else: self.dependency_processor.process_saves(uow, states) def per_state_flush_actions(self, uow): # this is handled by SaveUpdateAll and DeleteAll, # since a ProcessAll should unconditionally be pulled # into per-state if either the parent/child mappers # are part of a cycle return iter([]) def __repr__(self): return "%s(%s, isdelete=%s)" % ( self.__class__.__name__, self.dependency_processor, self.isdelete, ) def _elements(self, uow): for mapper in self._mappers(uow): for state in uow.mappers[mapper]: (isdelete, listonly) = uow.states[state] if isdelete == self.isdelete and not listonly: yield state class PostUpdateAll(PostSortRec): __slots__ = "mapper", "isdelete", "sort_key" def __init__(self, uow, mapper, isdelete): self.mapper = mapper self.isdelete = isdelete self.sort_key = ("PostUpdateAll", mapper._sort_key, isdelete) @util.preload_module("sqlalchemy.orm.persistence") def execute(self, uow): persistence = util.preloaded.orm_persistence states, cols = uow.post_update_states[self.mapper] states = [s for s in states if uow.states[s][0] == self.isdelete] persistence.post_update(self.mapper, states, uow, cols) class SaveUpdateAll(PostSortRec): __slots__ = ("mapper", "sort_key") def __init__(self, uow, mapper): self.mapper = mapper self.sort_key = ("SaveUpdateAll", mapper._sort_key) assert mapper is mapper.base_mapper @util.preload_module("sqlalchemy.orm.persistence") def execute(self, uow): util.preloaded.orm_persistence.save_obj( self.mapper, uow.states_for_mapper_hierarchy(self.mapper, False, False), uow, ) def per_state_flush_actions(self, uow): states = list( uow.states_for_mapper_hierarchy(self.mapper, False, False) ) base_mapper = self.mapper.base_mapper delete_all = DeleteAll(uow, base_mapper) for state in states: # keep saves before deletes - # this ensures 'row switch' operations work action = SaveUpdateState(uow, state) uow.dependencies.add((action, delete_all)) yield action for dep in uow.deps[self.mapper]: states_for_prop = uow.filter_states_for_dep(dep, states) dep.per_state_flush_actions(uow, states_for_prop, False) def __repr__(self): return "%s(%s)" % (self.__class__.__name__, self.mapper) class DeleteAll(PostSortRec): __slots__ = ("mapper", "sort_key") def __init__(self, uow, mapper): self.mapper = mapper self.sort_key = ("DeleteAll", mapper._sort_key) assert mapper is mapper.base_mapper @util.preload_module("sqlalchemy.orm.persistence") def execute(self, uow): util.preloaded.orm_persistence.delete_obj( self.mapper, uow.states_for_mapper_hierarchy(self.mapper, True, False), uow, ) def per_state_flush_actions(self, uow): states = list( uow.states_for_mapper_hierarchy(self.mapper, True, False) ) base_mapper = self.mapper.base_mapper save_all = SaveUpdateAll(uow, base_mapper) for state in states: # keep saves before deletes - # this ensures 'row switch' operations work action = DeleteState(uow, state) uow.dependencies.add((save_all, action)) yield action for dep in uow.deps[self.mapper]: states_for_prop = uow.filter_states_for_dep(dep, states) dep.per_state_flush_actions(uow, states_for_prop, True) def __repr__(self): return "%s(%s)" % (self.__class__.__name__, self.mapper) class ProcessState(PostSortRec): __slots__ = "dependency_processor", "isdelete", "state", "sort_key" def __init__(self, uow, dependency_processor, isdelete, state): self.dependency_processor = dependency_processor self.sort_key = ("ProcessState", dependency_processor.sort_key) self.isdelete = isdelete self.state = state def execute_aggregate(self, uow, recs): cls_ = self.__class__ dependency_processor = self.dependency_processor isdelete = self.isdelete our_recs = [ r for r in recs if r.__class__ is cls_ and r.dependency_processor is dependency_processor and r.isdelete is isdelete ] recs.difference_update(our_recs) states = [self.state] + [r.state for r in our_recs] if isdelete: dependency_processor.process_deletes(uow, states) else: dependency_processor.process_saves(uow, states) def __repr__(self): return "%s(%s, %s, delete=%s)" % ( self.__class__.__name__, self.dependency_processor, orm_util.state_str(self.state), self.isdelete, ) class SaveUpdateState(PostSortRec): __slots__ = "state", "mapper", "sort_key" def __init__(self, uow, state): self.state = state self.mapper = state.mapper.base_mapper self.sort_key = ("ProcessState", self.mapper._sort_key) @util.preload_module("sqlalchemy.orm.persistence") def execute_aggregate(self, uow, recs): persistence = util.preloaded.orm_persistence cls_ = self.__class__ mapper = self.mapper our_recs = [ r for r in recs if r.__class__ is cls_ and r.mapper is mapper ] recs.difference_update(our_recs) persistence.save_obj( mapper, [self.state] + [r.state for r in our_recs], uow ) def __repr__(self): return "%s(%s)" % ( self.__class__.__name__, orm_util.state_str(self.state), ) class DeleteState(PostSortRec): __slots__ = "state", "mapper", "sort_key" def __init__(self, uow, state): self.state = state self.mapper = state.mapper.base_mapper self.sort_key = ("DeleteState", self.mapper._sort_key) @util.preload_module("sqlalchemy.orm.persistence") def execute_aggregate(self, uow, recs): persistence = util.preloaded.orm_persistence cls_ = self.__class__ mapper = self.mapper our_recs = [ r for r in recs if r.__class__ is cls_ and r.mapper is mapper ] recs.difference_update(our_recs) states = [self.state] + [r.state for r in our_recs] persistence.delete_obj( mapper, [s for s in states if uow.states[s][0]], uow ) def __repr__(self): return "%s(%s)" % ( self.__class__.__name__, orm_util.state_str(self.state), )
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