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Unified Diff: venv/Lib/site-packages/django/db/models/deletion.py

Issue 554060043: testMe
Patch Set: Created 2 years, 10 months ago
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Index: venv/Lib/site-packages/django/db/models/deletion.py
===================================================================
new file mode 100644
--- /dev/null
+++ b/venv/Lib/site-packages/django/db/models/deletion.py
@@ -0,0 +1,319 @@
+from collections import Counter, OrderedDict
+from operator import attrgetter
+
+from django.db import IntegrityError, connections, transaction
+from django.db.models import signals, sql
+from django.utils import six
+
+
+class ProtectedError(IntegrityError):
+ def __init__(self, msg, protected_objects):
+ self.protected_objects = protected_objects
+ super(ProtectedError, self).__init__(msg, protected_objects)
+
+
+def CASCADE(collector, field, sub_objs, using):
+ collector.collect(sub_objs, source=field.remote_field.model,
+ source_attr=field.name, nullable=field.null)
+ if field.null and not connections[using].features.can_defer_constraint_checks:
+ collector.add_field_update(field, None, sub_objs)
+
+
+def PROTECT(collector, field, sub_objs, using):
+ raise ProtectedError(
+ "Cannot delete some instances of model '%s' because they are "
+ "referenced through a protected foreign key: '%s.%s'" % (
+ field.remote_field.model.__name__, sub_objs[0].__class__.__name__, field.name
+ ),
+ sub_objs
+ )
+
+
+def SET(value):
+ if callable(value):
+ def set_on_delete(collector, field, sub_objs, using):
+ collector.add_field_update(field, value(), sub_objs)
+ else:
+ def set_on_delete(collector, field, sub_objs, using):
+ collector.add_field_update(field, value, sub_objs)
+ set_on_delete.deconstruct = lambda: ('django.db.models.SET', (value,), {})
+ return set_on_delete
+
+
+def SET_NULL(collector, field, sub_objs, using):
+ collector.add_field_update(field, None, sub_objs)
+
+
+def SET_DEFAULT(collector, field, sub_objs, using):
+ collector.add_field_update(field, field.get_default(), sub_objs)
+
+
+def DO_NOTHING(collector, field, sub_objs, using):
+ pass
+
+
+def get_candidate_relations_to_delete(opts):
+ # The candidate relations are the ones that come from N-1 and 1-1 relations.
+ # N-N (i.e., many-to-many) relations aren't candidates for deletion.
+ return (
+ f for f in opts.get_fields(include_hidden=True)
+ if f.auto_created and not f.concrete and (f.one_to_one or f.one_to_many)
+ )
+
+
+class Collector(object):
+ def __init__(self, using):
+ self.using = using
+ # Initially, {model: {instances}}, later values become lists.
+ self.data = OrderedDict()
+ self.field_updates = {} # {model: {(field, value): {instances}}}
+ # fast_deletes is a list of queryset-likes that can be deleted without
+ # fetching the objects into memory.
+ self.fast_deletes = []
+
+ # Tracks deletion-order dependency for databases without transactions
+ # or ability to defer constraint checks. Only concrete model classes
+ # should be included, as the dependencies exist only between actual
+ # database tables; proxy models are represented here by their concrete
+ # parent.
+ self.dependencies = {} # {model: {models}}
+
+ def add(self, objs, source=None, nullable=False, reverse_dependency=False):
+ """
+ Adds '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.
+
+ Returns a list of all objects that were not already collected.
+ """
+ if not objs:
+ return []
+ new_objs = []
+ model = objs[0].__class__
+ instances = self.data.setdefault(model, set())
+ 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:
+ if reverse_dependency:
+ source, model = model, source
+ self.dependencies.setdefault(
+ source._meta.concrete_model, set()).add(model._meta.concrete_model)
+ return new_objs
+
+ def add_field_update(self, field, value, objs):
+ """
+ Schedules a field update. 'objs' must be a homogeneous iterable
+ collection of model instances (e.g. a QuerySet).
+ """
+ if not objs:
+ return
+ model = objs[0].__class__
+ self.field_updates.setdefault(
+ model, {}).setdefault(
+ (field, value), set()).update(objs)
+
+ def can_fast_delete(self, objs, from_field=None):
+ """
+ Determines if the objects in the given queryset-like 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. Allows 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 not (hasattr(objs, 'model') and hasattr(objs, '_raw_delete')):
+ return False
+ model = objs.model
+ if (signals.pre_delete.has_listeners(model) or
+ signals.post_delete.has_listeners(model) or
+ signals.m2m_changed.has_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
+ if any(link != from_field for link in opts.concrete_model._meta.parents.values()):
+ return False
+ # Foreign keys pointing to this model, both from m2m and other
+ # models.
+ for related in get_candidate_relations_to_delete(opts):
+ if related.field.remote_field.on_delete is not DO_NOTHING:
+ return False
+ for field in model._meta.private_fields:
+ if hasattr(field, 'bulk_related_objects'):
+ # It's something like generic foreign key.
+ return False
+ return True
+
+ def get_del_batches(self, objs, field):
+ """
+ Returns the objs in suitably sized batches for the used connection.
+ """
+ conn_batch_size = max(
+ connections[self.using].ops.bulk_batch_size([field.name], 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 collect(self, objs, source=None, nullable=False, collect_related=True,
+ source_attr=None, reverse_dependency=False, keep_parents=False):
+ """
+ Adds '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 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 six.itervalues(concrete_model._meta.parents):
+ 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)
+ if collect_related:
+ parents = model._meta.parents
+ 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
+ if field.remote_field.on_delete == DO_NOTHING:
+ continue
+ batches = self.get_del_batches(new_objs, field)
+ for batch in batches:
+ sub_objs = self.related_objects(related, batch)
+ if self.can_fast_delete(sub_objs, from_field=field):
+ self.fast_deletes.append(sub_objs)
+ elif sub_objs:
+ field.remote_field.on_delete(self, field, sub_objs, self.using)
+ 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)
+
+ def related_objects(self, related, objs):
+ """
+ Gets a QuerySet of objects related to ``objs`` via the relation ``related``.
+ """
+ return related.related_model._base_manager.using(self.using).filter(
+ **{"%s__in" % related.field.name: objs}
+ )
+
+ def instances_with_model(self):
+ for model, instances in six.iteritems(self.data):
+ for obj in instances:
+ yield model, obj
+
+ 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 = OrderedDict((model, self.data[model])
+ for model in sorted_models)
+
+ 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()
+
+ 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
+ )
+
+ # fast deletes
+ for qs in self.fast_deletes:
+ count = qs._raw_delete(using=self.using)
+ deleted_counter[qs.model._meta.label] += count
+
+ # update fields
+ for model, instances_for_fieldvalues in six.iteritems(self.field_updates):
+ for (field, value), instances in six.iteritems(instances_for_fieldvalues):
+ query = sql.UpdateQuery(model)
+ query.update_batch([obj.pk for obj in instances],
+ {field.name: value}, self.using)
+
+ # reverse instance collections
+ for instances in six.itervalues(self.data):
+ instances.reverse()
+
+ # delete instances
+ for model, instances in six.iteritems(self.data):
+ query = sql.DeleteQuery(model)
+ pk_list = [obj.pk for obj in instances]
+ count = query.delete_batch(pk_list, self.using)
+ 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
+ )
+
+ # update collected instances
+ for model, instances_for_fieldvalues in six.iteritems(self.field_updates):
+ for (field, value), instances in six.iteritems(instances_for_fieldvalues):
+ for obj in instances:
+ setattr(obj, field.attname, value)
+ for model, instances in six.iteritems(self.data):
+ for instance in instances:
+ setattr(instance, model._meta.pk.attname, None)
+ return sum(deleted_counter.values()), dict(deleted_counter)
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