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# orm/unitofwork.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
"""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 . import attributes
from . import exc as orm_exc
from . import persistence
from . import util as orm_util
from .. import event
from .. import util
from ..util import topological
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):
# 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 (prop.cascade_backrefs or key == initiator.key)
and not sess._contains_state(item_state)
):
sess._save_or_update_state(item_state)
return item
def remove(state, item, initiator):
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):
# 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 (prop.cascade_backrefs or 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", append, raw=True, retval=True)
event.listen(descriptor, "remove", remove, raw=True, retval=True)
event.listen(descriptor, "set", set_, raw=True, retval=True)
class UOWTransaction(object):
def __init__(self, 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,
)
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
)
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,
isdelete=False,
listonly=False,
cancel_delete=False,
operation=None,
prop=None,
):
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 = dict(
(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 set(
[a for a in self.postsort_actions.values() if not a.disabled]
).difference(cycles)
def execute(self):
postsort_actions = self._generate_actions()
# 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 set_ in topological.sort_as_subsets(
self.dependencies, postsort_actions
):
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):
"""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 = set(
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(object):
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(object):
__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"
def __init__(self, uow, dependency_processor, isdelete, fromparent):
self.dependency_processor = dependency_processor
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"
def __init__(self, uow, mapper, isdelete):
self.mapper = mapper
self.isdelete = isdelete
def execute(self, uow):
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",)
def __init__(self, uow, mapper):
self.mapper = mapper
assert mapper is mapper.base_mapper
def execute(self, uow):
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",)
def __init__(self, uow, mapper):
self.mapper = mapper
assert mapper is mapper.base_mapper
def execute(self, uow):
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"
def __init__(self, uow, dependency_processor, isdelete, state):
self.dependency_processor = dependency_processor
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"
def __init__(self, uow, state):
self.state = state
self.mapper = state.mapper.base_mapper
def execute_aggregate(self, uow, recs):
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"
def __init__(self, uow, state):
self.state = state
self.mapper = state.mapper.base_mapper
def execute_aggregate(self, uow, recs):
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),
)