class Collector
from django.db.models.deletion import Collector
Ancestors (MRO)
def add(self, objs, source=None, nullable=False, reverse_dependency=False)
django.db.models.deletion.Collector
Add 'objs' to the collection of objects to be deleted. If the call is the result of a cascade, 'source' should be the model that caused it, and 'nullable' should be set to True if the relation can be null. Return a list of all objects that were not already collected.
def add(self, objs, source=None, nullable=False, reverse_dependency=False):
"""
Add 'objs' to the collection of objects to be deleted. If the call is
the result of a cascade, 'source' should be the model that caused it,
and 'nullable' should be set to True if the relation can be null.
Return a list of all objects that were not already collected.
"""
if not objs:
return []
new_objs = []
model = objs[0].__class__
instances = self.data[model]
for obj in objs:
if obj not in instances:
new_objs.append(obj)
instances.update(new_objs)
# Nullable relationships can be ignored -- they are nulled out before
# deleting, and therefore do not affect the order in which objects have
# to be deleted.
if source is not None and not nullable:
self.add_dependency(source, model, reverse_dependency=reverse_dependency)
return new_objs
def add_dependency(self, model, dependency, reverse_dependency=False)
django.db.models.deletion.Collector
def add_dependency(self, model, dependency, reverse_dependency=False):
if reverse_dependency:
model, dependency = dependency, model
self.dependencies[model._meta.concrete_model].add(
dependency._meta.concrete_model
)
self.data.setdefault(dependency, self.data.default_factory())
def add_field_update(self, field, value, objs)
django.db.models.deletion.Collector
Schedule a field update. 'objs' must be a homogeneous iterable collection of model instances (e.g. a QuerySet).
def add_field_update(self, field, value, objs):
"""
Schedule a field update. 'objs' must be a homogeneous iterable
collection of model instances (e.g. a QuerySet).
"""
self.field_updates[field, value].append(objs)
def add_restricted_objects(self, field, objs)
django.db.models.deletion.Collector
def add_restricted_objects(self, field, objs):
if objs:
model = objs[0].__class__
self.restricted_objects[model][field].update(objs)
def can_fast_delete(self, objs, from_field=None)
django.db.models.deletion.Collector
Determine if the objects in the given queryset-like or single object can be fast-deleted. This can be done if there are no cascades, no parents and no signal listeners for the object class. The 'from_field' tells where we are coming from - we need this to determine if the objects are in fact to be deleted. Allow also skipping parent -> child -> parent chain preventing fast delete of the child.
def can_fast_delete(self, objs, from_field=None):
"""
Determine if the objects in the given queryset-like or single object
can be fast-deleted. This can be done if there are no cascades, no
parents and no signal listeners for the object class.
The 'from_field' tells where we are coming from - we need this to
determine if the objects are in fact to be deleted. Allow also
skipping parent -> child -> parent chain preventing fast delete of
the child.
"""
if from_field and from_field.remote_field.on_delete is not CASCADE:
return False
if hasattr(objs, "_meta"):
model = objs._meta.model
elif hasattr(objs, "model") and hasattr(objs, "_raw_delete"):
model = objs.model
else:
return False
if self._has_signal_listeners(model):
return False
# The use of from_field comes from the need to avoid cascade back to
# parent when parent delete is cascading to child.
opts = model._meta
return (
all(
link == from_field
for link in opts.concrete_model._meta.parents.values()
)
and
# Foreign keys pointing to this model.
all(
related.field.remote_field.on_delete is DO_NOTHING
for related in get_candidate_relations_to_delete(opts)
)
and (
# Something like generic foreign key.
not any(
hasattr(field, "bulk_related_objects")
for field in opts.private_fields
)
)
)
def clear_restricted_objects_from_queryset(self, model, qs)
django.db.models.deletion.Collector
def clear_restricted_objects_from_queryset(self, model, qs):
if model in self.restricted_objects:
objs = set(
qs.filter(
pk__in=[
obj.pk
for objs in self.restricted_objects[model].values()
for obj in objs
]
)
)
self.clear_restricted_objects_from_set(model, objs)
def clear_restricted_objects_from_set(self, model, objs)
django.db.models.deletion.Collector
def clear_restricted_objects_from_set(self, model, objs):
if model in self.restricted_objects:
self.restricted_objects[model] = {
field: items - objs
for field, items in self.restricted_objects[model].items()
}
def collect(self, objs, source=None, nullable=False, collect_related=True, source_attr=None, reverse_dependency=False, keep_parents=False, fail_on_restricted=True)
django.db.models.deletion.Collector
Add 'objs' to the collection of objects to be deleted as well as all parent instances. 'objs' must be a homogeneous iterable collection of model instances (e.g. a QuerySet). If 'collect_related' is True, related objects will be handled by their respective on_delete handler. If the call is the result of a cascade, 'source' should be the model that caused it and 'nullable' should be set to True, if the relation can be null. If 'reverse_dependency' is True, 'source' will be deleted before the current model, rather than after. (Needed for cascading to parent models, the one case in which the cascade follows the forwards direction of an FK rather than the reverse direction.) If 'keep_parents' is True, data of parent model's will be not deleted. If 'fail_on_restricted' is False, error won't be raised even if it's prohibited to delete such objects due to RESTRICT, that defers restricted object checking in recursive calls where the top-level call may need to collect more objects to determine whether restricted ones can be deleted.
def collect(
self,
objs,
source=None,
nullable=False,
collect_related=True,
source_attr=None,
reverse_dependency=False,
keep_parents=False,
fail_on_restricted=True,
):
"""
Add 'objs' to the collection of objects to be deleted as well as all
parent instances. 'objs' must be a homogeneous iterable collection of
model instances (e.g. a QuerySet). If 'collect_related' is True,
related objects will be handled by their respective on_delete handler.
If the call is the result of a cascade, 'source' should be the model
that caused it and 'nullable' should be set to True, if the relation
can be null.
If 'reverse_dependency' is True, 'source' will be deleted before the
current model, rather than after. (Needed for cascading to parent
models, the one case in which the cascade follows the forwards
direction of an FK rather than the reverse direction.)
If 'keep_parents' is True, data of parent model's will be not deleted.
If 'fail_on_restricted' is False, error won't be raised even if it's
prohibited to delete such objects due to RESTRICT, that defers
restricted object checking in recursive calls where the top-level call
may need to collect more objects to determine whether restricted ones
can be deleted.
"""
if self.can_fast_delete(objs):
self.fast_deletes.append(objs)
return
new_objs = self.add(
objs, source, nullable, reverse_dependency=reverse_dependency
)
if not new_objs:
return
model = new_objs[0].__class__
if not keep_parents:
# Recursively collect concrete model's parent models, but not their
# related objects. These will be found by meta.get_fields()
concrete_model = model._meta.concrete_model
for ptr in concrete_model._meta.parents.values():
if ptr:
parent_objs = [getattr(obj, ptr.name) for obj in new_objs]
self.collect(
parent_objs,
source=model,
source_attr=ptr.remote_field.related_name,
collect_related=False,
reverse_dependency=True,
fail_on_restricted=False,
)
if not collect_related:
return
if keep_parents:
parents = set(model._meta.get_parent_list())
model_fast_deletes = defaultdict(list)
protected_objects = defaultdict(list)
for related in get_candidate_relations_to_delete(model._meta):
# Preserve parent reverse relationships if keep_parents=True.
if keep_parents and related.model in parents:
continue
field = related.field
on_delete = field.remote_field.on_delete
if on_delete == DO_NOTHING:
continue
related_model = related.related_model
if self.can_fast_delete(related_model, from_field=field):
model_fast_deletes[related_model].append(field)
continue
batches = self.get_del_batches(new_objs, [field])
for batch in batches:
sub_objs = self.related_objects(related_model, [field], batch)
# Non-referenced fields can be deferred if no signal receivers
# are connected for the related model as they'll never be
# exposed to the user. Skip field deferring when some
# relationships are select_related as interactions between both
# features are hard to get right. This should only happen in
# the rare cases where .related_objects is overridden anyway.
if not (
sub_objs.query.select_related
or self._has_signal_listeners(related_model)
):
referenced_fields = set(
chain.from_iterable(
(rf.attname for rf in rel.field.foreign_related_fields)
for rel in get_candidate_relations_to_delete(
related_model._meta
)
)
)
sub_objs = sub_objs.only(*tuple(referenced_fields))
if getattr(on_delete, "lazy_sub_objs", False) or sub_objs:
try:
on_delete(self, field, sub_objs, self.using)
except ProtectedError as error:
key = "'%s.%s'" % (field.model.__name__, field.name)
protected_objects[key] += error.protected_objects
if protected_objects:
raise ProtectedError(
"Cannot delete some instances of model %r because they are "
"referenced through protected foreign keys: %s."
% (
model.__name__,
", ".join(protected_objects),
),
set(chain.from_iterable(protected_objects.values())),
)
for related_model, related_fields in model_fast_deletes.items():
batches = self.get_del_batches(new_objs, related_fields)
for batch in batches:
sub_objs = self.related_objects(related_model, related_fields, batch)
self.fast_deletes.append(sub_objs)
for field in model._meta.private_fields:
if hasattr(field, "bulk_related_objects"):
# It's something like generic foreign key.
sub_objs = field.bulk_related_objects(new_objs, self.using)
self.collect(
sub_objs, source=model, nullable=True, fail_on_restricted=False
)
if fail_on_restricted:
# Raise an error if collected restricted objects (RESTRICT) aren't
# candidates for deletion also collected via CASCADE.
for related_model, instances in self.data.items():
self.clear_restricted_objects_from_set(related_model, instances)
for qs in self.fast_deletes:
self.clear_restricted_objects_from_queryset(qs.model, qs)
if self.restricted_objects.values():
restricted_objects = defaultdict(list)
for related_model, fields in self.restricted_objects.items():
for field, objs in fields.items():
if objs:
key = "'%s.%s'" % (related_model.__name__, field.name)
restricted_objects[key] += objs
if restricted_objects:
raise RestrictedError(
"Cannot delete some instances of model %r because "
"they are referenced through restricted foreign keys: "
"%s."
% (
model.__name__,
", ".join(restricted_objects),
),
set(chain.from_iterable(restricted_objects.values())),
)
def delete(self)
django.db.models.deletion.Collector
def delete(self):
# sort instance collections
for model, instances in self.data.items():
self.data[model] = sorted(instances, key=attrgetter("pk"))
# if possible, bring the models in an order suitable for databases that
# don't support transactions or cannot defer constraint checks until the
# end of a transaction.
self.sort()
# number of objects deleted for each model label
deleted_counter = Counter()
# Optimize for the case with a single obj and no dependencies
if len(self.data) == 1 and len(instances) == 1:
instance = list(instances)[0]
if self.can_fast_delete(instance):
with transaction.mark_for_rollback_on_error(self.using):
count = sql.DeleteQuery(model).delete_batch(
[instance.pk], self.using
)
setattr(instance, model._meta.pk.attname, None)
return count, {model._meta.label: count}
with transaction.atomic(using=self.using, savepoint=False):
# send pre_delete signals
for model, obj in self.instances_with_model():
if not model._meta.auto_created:
signals.pre_delete.send(
sender=model,
instance=obj,
using=self.using,
origin=self.origin,
)
# fast deletes
for qs in self.fast_deletes:
count = qs._raw_delete(using=self.using)
if count:
deleted_counter[qs.model._meta.label] += count
# update fields
for (field, value), instances_list in self.field_updates.items():
updates = []
objs = []
for instances in instances_list:
if (
isinstance(instances, models.QuerySet)
and instances._result_cache is None
):
updates.append(instances)
else:
objs.extend(instances)
if updates:
combined_updates = reduce(or_, updates)
combined_updates.update(**{field.name: value})
if objs:
model = objs[0].__class__
query = sql.UpdateQuery(model)
query.update_batch(
list({obj.pk for obj in objs}), {field.name: value}, self.using
)
# reverse instance collections
for instances in self.data.values():
instances.reverse()
# delete instances
for model, instances in self.data.items():
query = sql.DeleteQuery(model)
pk_list = [obj.pk for obj in instances]
count = query.delete_batch(pk_list, self.using)
if count:
deleted_counter[model._meta.label] += count
if not model._meta.auto_created:
for obj in instances:
signals.post_delete.send(
sender=model,
instance=obj,
using=self.using,
origin=self.origin,
)
for model, instances in self.data.items():
for instance in instances:
setattr(instance, model._meta.pk.attname, None)
return sum(deleted_counter.values()), dict(deleted_counter)
def get_del_batches(self, objs, fields)
django.db.models.deletion.Collector
Return the objs in suitably sized batches for the used connection.
def get_del_batches(self, objs, fields):
"""
Return the objs in suitably sized batches for the used connection.
"""
field_names = [field.name for field in fields]
conn_batch_size = max(
connections[self.using].ops.bulk_batch_size(field_names, objs), 1
)
if len(objs) > conn_batch_size:
return [
objs[i : i + conn_batch_size]
for i in range(0, len(objs), conn_batch_size)
]
else:
return [objs]
def instances_with_model(self)
django.db.models.deletion.Collector
def instances_with_model(self):
for model, instances in self.data.items():
for obj in instances:
yield model, obj
def related_objects(self, related_model, related_fields, objs)
django.db.models.deletion.Collector
Get a QuerySet of the related model to objs via related fields.
def related_objects(self, related_model, related_fields, objs):
"""
Get a QuerySet of the related model to objs via related fields.
"""
predicate = query_utils.Q.create(
[(f"{related_field.name}__in", objs) for related_field in related_fields],
connector=query_utils.Q.OR,
)
return related_model._base_manager.using(self.using).filter(predicate)
def sort(self)
django.db.models.deletion.Collector
def sort(self):
sorted_models = []
concrete_models = set()
models = list(self.data)
while len(sorted_models) < len(models):
found = False
for model in models:
if model in sorted_models:
continue
dependencies = self.dependencies.get(model._meta.concrete_model)
if not (dependencies and dependencies.difference(concrete_models)):
sorted_models.append(model)
concrete_models.add(model._meta.concrete_model)
found = True
if not found:
return
self.data = {model: self.data[model] for model in sorted_models}