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350 lines
15 KiB
Python
350 lines
15 KiB
Python
5 years ago
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from collections import Counter
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from itertools import chain
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from operator import attrgetter
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from django.db import IntegrityError, connections, transaction
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from django.db.models import signals, sql
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class ProtectedError(IntegrityError):
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def __init__(self, msg, protected_objects):
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self.protected_objects = protected_objects
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super().__init__(msg, protected_objects)
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def CASCADE(collector, field, sub_objs, using):
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collector.collect(sub_objs, source=field.remote_field.model,
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source_attr=field.name, nullable=field.null)
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if field.null and not connections[using].features.can_defer_constraint_checks:
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collector.add_field_update(field, None, sub_objs)
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def PROTECT(collector, field, sub_objs, using):
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raise ProtectedError(
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"Cannot delete some instances of model '%s' because they are "
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"referenced through a protected foreign key: '%s.%s'" % (
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field.remote_field.model.__name__, sub_objs[0].__class__.__name__, field.name
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),
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sub_objs
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)
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def SET(value):
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if callable(value):
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def set_on_delete(collector, field, sub_objs, using):
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collector.add_field_update(field, value(), sub_objs)
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else:
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def set_on_delete(collector, field, sub_objs, using):
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collector.add_field_update(field, value, sub_objs)
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set_on_delete.deconstruct = lambda: ('django.db.models.SET', (value,), {})
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return set_on_delete
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def SET_NULL(collector, field, sub_objs, using):
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collector.add_field_update(field, None, sub_objs)
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def SET_DEFAULT(collector, field, sub_objs, using):
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collector.add_field_update(field, field.get_default(), sub_objs)
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def DO_NOTHING(collector, field, sub_objs, using):
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pass
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def get_candidate_relations_to_delete(opts):
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# The candidate relations are the ones that come from N-1 and 1-1 relations.
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# N-N (i.e., many-to-many) relations aren't candidates for deletion.
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return (
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f for f in opts.get_fields(include_hidden=True)
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if f.auto_created and not f.concrete and (f.one_to_one or f.one_to_many)
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)
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class Collector:
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def __init__(self, using):
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self.using = using
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# Initially, {model: {instances}}, later values become lists.
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self.data = {}
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self.field_updates = {} # {model: {(field, value): {instances}}}
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# fast_deletes is a list of queryset-likes that can be deleted without
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# fetching the objects into memory.
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self.fast_deletes = []
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# Tracks deletion-order dependency for databases without transactions
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# or ability to defer constraint checks. Only concrete model classes
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# should be included, as the dependencies exist only between actual
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# database tables; proxy models are represented here by their concrete
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# parent.
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self.dependencies = {} # {model: {models}}
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def add(self, objs, source=None, nullable=False, reverse_dependency=False):
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"""
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Add 'objs' to the collection of objects to be deleted. If the call is
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the result of a cascade, 'source' should be the model that caused it,
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and 'nullable' should be set to True if the relation can be null.
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Return a list of all objects that were not already collected.
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"""
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if not objs:
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return []
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new_objs = []
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model = objs[0].__class__
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instances = self.data.setdefault(model, set())
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for obj in objs:
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if obj not in instances:
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new_objs.append(obj)
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instances.update(new_objs)
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# Nullable relationships can be ignored -- they are nulled out before
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# deleting, and therefore do not affect the order in which objects have
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# to be deleted.
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if source is not None and not nullable:
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if reverse_dependency:
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source, model = model, source
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self.dependencies.setdefault(
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source._meta.concrete_model, set()).add(model._meta.concrete_model)
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return new_objs
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def add_field_update(self, field, value, objs):
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"""
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Schedule a field update. 'objs' must be a homogeneous iterable
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collection of model instances (e.g. a QuerySet).
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"""
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if not objs:
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return
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model = objs[0].__class__
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self.field_updates.setdefault(
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model, {}).setdefault(
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(field, value), set()).update(objs)
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def _has_signal_listeners(self, model):
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return (
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signals.pre_delete.has_listeners(model) or
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signals.post_delete.has_listeners(model)
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)
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def can_fast_delete(self, objs, from_field=None):
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"""
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Determine if the objects in the given queryset-like or single object
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can be fast-deleted. This can be done if there are no cascades, no
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parents and no signal listeners for the object class.
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The 'from_field' tells where we are coming from - we need this to
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determine if the objects are in fact to be deleted. Allow also
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skipping parent -> child -> parent chain preventing fast delete of
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the child.
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"""
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if from_field and from_field.remote_field.on_delete is not CASCADE:
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return False
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if hasattr(objs, '_meta'):
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model = type(objs)
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elif hasattr(objs, 'model') and hasattr(objs, '_raw_delete'):
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model = objs.model
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else:
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return False
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if self._has_signal_listeners(model):
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return False
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# The use of from_field comes from the need to avoid cascade back to
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# parent when parent delete is cascading to child.
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opts = model._meta
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return (
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all(link == from_field for link in opts.concrete_model._meta.parents.values()) and
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# Foreign keys pointing to this model.
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all(
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related.field.remote_field.on_delete is DO_NOTHING
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for related in get_candidate_relations_to_delete(opts)
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) and (
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# Something like generic foreign key.
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not any(hasattr(field, 'bulk_related_objects') for field in opts.private_fields)
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)
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)
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def get_del_batches(self, objs, field):
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"""
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Return the objs in suitably sized batches for the used connection.
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"""
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conn_batch_size = max(
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connections[self.using].ops.bulk_batch_size([field.name], objs), 1)
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if len(objs) > conn_batch_size:
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return [objs[i:i + conn_batch_size]
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for i in range(0, len(objs), conn_batch_size)]
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else:
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return [objs]
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def collect(self, objs, source=None, nullable=False, collect_related=True,
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source_attr=None, reverse_dependency=False, keep_parents=False):
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"""
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Add 'objs' to the collection of objects to be deleted as well as all
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parent instances. 'objs' must be a homogeneous iterable collection of
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model instances (e.g. a QuerySet). If 'collect_related' is True,
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related objects will be handled by their respective on_delete handler.
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If the call is the result of a cascade, 'source' should be the model
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that caused it and 'nullable' should be set to True, if the relation
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can be null.
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If 'reverse_dependency' is True, 'source' will be deleted before the
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current model, rather than after. (Needed for cascading to parent
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models, the one case in which the cascade follows the forwards
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direction of an FK rather than the reverse direction.)
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If 'keep_parents' is True, data of parent model's will be not deleted.
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"""
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if self.can_fast_delete(objs):
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self.fast_deletes.append(objs)
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return
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new_objs = self.add(objs, source, nullable,
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reverse_dependency=reverse_dependency)
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if not new_objs:
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return
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model = new_objs[0].__class__
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if not keep_parents:
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# Recursively collect concrete model's parent models, but not their
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# related objects. These will be found by meta.get_fields()
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concrete_model = model._meta.concrete_model
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for ptr in concrete_model._meta.parents.values():
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if ptr:
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parent_objs = [getattr(obj, ptr.name) for obj in new_objs]
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self.collect(parent_objs, source=model,
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source_attr=ptr.remote_field.related_name,
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collect_related=False,
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reverse_dependency=True)
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if collect_related:
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if keep_parents:
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parents = set(model._meta.get_parent_list())
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for related in get_candidate_relations_to_delete(model._meta):
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# Preserve parent reverse relationships if keep_parents=True.
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if keep_parents and related.model in parents:
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continue
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field = related.field
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if field.remote_field.on_delete == DO_NOTHING:
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continue
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batches = self.get_del_batches(new_objs, field)
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for batch in batches:
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sub_objs = self.related_objects(related, batch)
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if self.can_fast_delete(sub_objs, from_field=field):
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self.fast_deletes.append(sub_objs)
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else:
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related_model = related.related_model
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# Non-referenced fields can be deferred if no signal
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# receivers are connected for the related model as
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# they'll never be exposed to the user. Skip field
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# deferring when some relationships are select_related
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# as interactions between both features are hard to
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# get right. This should only happen in the rare
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# cases where .related_objects is overridden anyway.
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if not (sub_objs.query.select_related or self._has_signal_listeners(related_model)):
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referenced_fields = set(chain.from_iterable(
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(rf.attname for rf in rel.field.foreign_related_fields)
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for rel in get_candidate_relations_to_delete(related_model._meta)
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))
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sub_objs = sub_objs.only(*tuple(referenced_fields))
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if sub_objs:
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field.remote_field.on_delete(self, field, sub_objs, self.using)
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for field in model._meta.private_fields:
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if hasattr(field, 'bulk_related_objects'):
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# It's something like generic foreign key.
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sub_objs = field.bulk_related_objects(new_objs, self.using)
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self.collect(sub_objs, source=model, nullable=True)
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def related_objects(self, related, objs):
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"""
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Get a QuerySet of objects related to `objs` via the relation `related`.
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"""
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return related.related_model._base_manager.using(self.using).filter(
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**{"%s__in" % related.field.name: objs}
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)
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def instances_with_model(self):
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for model, instances in self.data.items():
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for obj in instances:
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yield model, obj
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def sort(self):
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sorted_models = []
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concrete_models = set()
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models = list(self.data)
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while len(sorted_models) < len(models):
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found = False
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for model in models:
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if model in sorted_models:
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continue
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dependencies = self.dependencies.get(model._meta.concrete_model)
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if not (dependencies and dependencies.difference(concrete_models)):
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sorted_models.append(model)
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concrete_models.add(model._meta.concrete_model)
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found = True
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if not found:
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return
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self.data = {model: self.data[model] for model in sorted_models}
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def delete(self):
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# sort instance collections
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for model, instances in self.data.items():
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self.data[model] = sorted(instances, key=attrgetter("pk"))
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# if possible, bring the models in an order suitable for databases that
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# don't support transactions or cannot defer constraint checks until the
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# end of a transaction.
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self.sort()
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# number of objects deleted for each model label
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deleted_counter = Counter()
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# Optimize for the case with a single obj and no dependencies
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if len(self.data) == 1 and len(instances) == 1:
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instance = list(instances)[0]
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if self.can_fast_delete(instance):
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with transaction.mark_for_rollback_on_error():
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count = sql.DeleteQuery(model).delete_batch([instance.pk], self.using)
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setattr(instance, model._meta.pk.attname, None)
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return count, {model._meta.label: count}
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with transaction.atomic(using=self.using, savepoint=False):
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# send pre_delete signals
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for model, obj in self.instances_with_model():
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if not model._meta.auto_created:
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signals.pre_delete.send(
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sender=model, instance=obj, using=self.using
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)
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# fast deletes
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for qs in self.fast_deletes:
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count = qs._raw_delete(using=self.using)
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deleted_counter[qs.model._meta.label] += count
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# update fields
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for model, instances_for_fieldvalues in self.field_updates.items():
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for (field, value), instances in instances_for_fieldvalues.items():
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query = sql.UpdateQuery(model)
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query.update_batch([obj.pk for obj in instances],
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{field.name: value}, self.using)
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# reverse instance collections
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for instances in self.data.values():
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instances.reverse()
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# delete instances
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for model, instances in self.data.items():
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query = sql.DeleteQuery(model)
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pk_list = [obj.pk for obj in instances]
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count = query.delete_batch(pk_list, self.using)
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deleted_counter[model._meta.label] += count
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if not model._meta.auto_created:
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for obj in instances:
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signals.post_delete.send(
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sender=model, instance=obj, using=self.using
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)
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# update collected instances
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for instances_for_fieldvalues in self.field_updates.values():
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for (field, value), instances in instances_for_fieldvalues.items():
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for obj in instances:
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setattr(obj, field.attname, value)
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for model, instances in self.data.items():
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for instance in instances:
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setattr(instance, model._meta.pk.attname, None)
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return sum(deleted_counter.values()), dict(deleted_counter)
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