patched M2M manager with signals (Django)

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class ForeignRelatedObjectsDescriptor(object):
# This class provides the functionality that makes the related-object
# managers available as attributes on a model class, for fields that have
# multiple "remote" values and have a ForeignKey pointed at them by
# some other model. In the example "poll.choice_set", the choice_set
# attribute is a ForeignRelatedObjectsDescriptor instance.
def __init__(self, related):
self.related = related # RelatedObject instance
def __get__(self, instance, instance_type=None):
if instance is None:
raise AttributeError, "Manager must be accessed via instance"
rel_field = self.related.field
rel_model = self.related.model
# Dynamically create a class that subclasses the related
# model's default manager.
superclass = self.related.model._default_manager.__class__
class RelatedManager(superclass):
def get_query_set(self):
return superclass.get_query_set(self).filter(**(self.core_filters))
def add(self, *objs):
for obj in objs:
setattr(obj, rel_field.name, instance)
obj.save()
add.alters_data = True
def create(self, **kwargs):
new_obj = self.model(**kwargs)
self.add(new_obj)
return new_obj
create.alters_data = True
# remove() and clear() are only provided if the ForeignKey can have a value of null.
if rel_field.null:
def remove(self, *objs):
val = getattr(instance, rel_field.rel.get_related_field().attname)
for obj in objs:
# Is obj actually part of this descriptor set?
if getattr(obj, rel_field.attname) == val:
setattr(obj, rel_field.name, None)
obj.save()
else:
raise rel_field.rel.to.DoesNotExist, "%r is not related to %r." % (obj, instance)
remove.alters_data = True
def clear(self):
for obj in self.all():
setattr(obj, rel_field.name, None)
obj.save()
clear.alters_data = True
manager = RelatedManager()
attname = rel_field.rel.get_related_field().name
manager.core_filters = {'%s__%s' % (rel_field.name, attname):
getattr(instance, attname)}
manager.model = self.related.model
return manager
def __set__(self, instance, value):
if instance is None:
raise AttributeError, "Manager must be accessed via instance"
manager = self.__get__(instance)
# If the foreign key can support nulls, then completely clear the related set.
# Otherwise, just move the named objects into the set.
if self.related.field.null:
manager.clear()
manager.add(*value)
def create_many_related_manager(superclass):
"""Creates a manager that subclasses 'superclass' (which is a Manager)
and adds behavior for many-to-many related objects."""
class ManyRelatedManager(superclass):
def __init__(self, model=None, core_filters=None, instance=None,
symmetrical=None, join_table=None, source_col_name=None,
target_col_name=None, field_name=None):
super(ManyRelatedManager, self).__init__()
self.core_filters = core_filters
self.model = model
self.symmetrical = symmetrical
self.instance = instance
self.join_table = join_table
self.source_col_name = source_col_name
self.target_col_name = target_col_name
self._pk_val = self.instance._get_pk_val()
self.field_name = field_name
if self._pk_val is None:
raise ValueError("%r instance needs to have a primary key value before a many-to-many relationship can be used." % instance.__class__.__name__)
def get_query_set(self):
return superclass.get_query_set(self).filter(**(self.core_filters))
def add(self, *objs):
self._add_items(self.source_col_name, self.target_col_name, *objs)
# If this is a symmetrical m2m relation to self, add the mirror entry in the m2m table
if self.symmetrical:
self._add_items(self.target_col_name, self.source_col_name, *objs)
add.alters_data = True
def remove(self, *objs):
self._remove_items(self.source_col_name, self.target_col_name, *objs)
# If this is a symmetrical m2m relation to self, remove the mirror entry in the m2m table
if self.symmetrical:
self._remove_items(self.target_col_name, self.source_col_name, *objs)
remove.alters_data = True
def clear(self):
self._clear_items(self.source_col_name)
# If this is a symmetrical m2m relation to self, clear the mirror entry in the m2m table
if self.symmetrical:
self._clear_items(self.target_col_name)
clear.alters_data = True
def create(self, **kwargs):
new_obj = self.model(**kwargs)
new_obj.save()
self.add(new_obj)
return new_obj
create.alters_data = True
def _add_items(self, source_col_name, target_col_name, *objs):
# join_table: name of the m2m link table
# source_col_name: the PK colname in join_table for the source object
# target_col_name: the PK colname in join_table for the target object
# *objs - objects to add. Either object instances, or primary keys of object instances.
# If there aren't any objects, there is nothing to do.
if objs:
# Check that all the objects are of the right type
new_ids = set()
for obj in objs:
if isinstance(obj, self.model):
new_ids.add(obj._get_pk_val())
else:
new_ids.add(obj)
# Add the newly created or already existing objects to the join table.
# First find out which items are already added, to avoid adding them twice
cursor = connection.cursor()
cursor.execute("SELECT %s FROM %s WHERE %s = %%s AND %s IN (%s)" % \
(target_col_name, self.join_table, source_col_name,
target_col_name, ",".join(['%s'] * len(new_ids))),
[self._pk_val] + list(new_ids))
existing_ids = set([row[0] for row in cursor.fetchall()])
# Add the ones that aren't there already
new_ids = new_ids - existing_ids
for obj_id in new_ids:
cursor.execute("INSERT INTO %s (%s, %s) VALUES (%%s, %%s)" % \
(self.join_table, source_col_name, target_col_name),
[self._pk_val, obj_id])
added_objs = [obj for obj in objs if (isinstance(obj, self.model) and obj._get_pk_val() in new_ids) or obj in new_ids]
dispatcher.send(signal=signals.m2m_add_items, sender=self.model,
instance=self.instance, field_name=self.field_name,
objs=added_objs)
transaction.commit_unless_managed()
def _remove_items(self, source_col_name, target_col_name, *objs):
# source_col_name: the PK colname in join_table for the source object
# target_col_name: the PK colname in join_table for the target object
# *objs - objects to remove
# If there aren't any objects, there is nothing to do.
if objs:
# Check that all the objects are of the right type
old_ids = set()
for obj in objs:
if isinstance(obj, self.model):
old_ids.add(obj._get_pk_val())
else:
old_ids.add(obj)
# Remove the specified objects from the join table
cursor = connection.cursor()
cursor.execute("DELETE FROM %s WHERE %s = %%s AND %s IN (%s)" % \
(self.join_table, source_col_name,
target_col_name, ",".join(['%s'] * len(old_ids))),
[self._pk_val] + list(old_ids))
dispatcher.send(signal=signals.m2m_remove_items, sender=self.model,
instance=self.instance, field_name=self.field_name,
objs=objs)
transaction.commit_unless_managed()
def _clear_items(self, source_col_name):
# source_col_name: the PK colname in join_table for the source object
dispatcher.send(signal=signals.m2m_clear_items, sender=self.model,
instance=self.instance, field_name=self.field_name)
cursor = connection.cursor()
cursor.execute("DELETE FROM %s WHERE %s = %%s" % \
(self.join_table, source_col_name),
[self._pk_val])
transaction.commit_unless_managed()
return ManyRelatedManager