Fixed #5390 -- Added signals for m2m operations. Thanks to the many p…

…eople (including, most recently, rvdrijst and frans) that have contributed to this patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@12223 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/fields/related.py

@@ -427,7 +427,8 @@ def create_many_related_manager(superclass, rel=False):
     through = rel.through
     class ManyRelatedManager(superclass):
         def __init__(self, model=None, core_filters=None, instance=None, symmetrical=None,
-                join_table=None, source_field_name=None, target_field_name=None):
+                join_table=None, source_field_name=None, target_field_name=None,
+                reverse=False):
             super(ManyRelatedManager, self).__init__()
             self.core_filters = core_filters
             self.model = model
@@ -437,6 +438,7 @@ def __init__(self, model=None, core_filters=None, instance=None, symmetrical=Non
             self.target_field_name = target_field_name
             self.through = through
             self._pk_val = self.instance.pk
+            self.reverse = reverse
             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__)
 
@@ -516,14 +518,19 @@ def _add_items(self, source_field_name, target_field_name, *objs):
                     source_field_name: self._pk_val,
                     '%s__in' % target_field_name: new_ids,
                 })
-                vals = set(vals)
-
+                new_ids = new_ids - set(vals)
                 # Add the ones that aren't there already
-                for obj_id in (new_ids - vals):
+                for obj_id in new_ids:
                     self.through._default_manager.using(self.instance._state.db).create(**{
                         '%s_id' % source_field_name: self._pk_val,
                         '%s_id' % target_field_name: obj_id,
                     })
+                if self.reverse or source_field_name == self.source_field_name:
+                    # Don't send the signal when we are inserting the
+                    # duplicate data row for symmetrical reverse entries.
+                    signals.m2m_changed.send(sender=rel.through, action='add',
+                        instance=self.instance, reverse=self.reverse,
+                        model=self.model, pk_set=new_ids)
 
         def _remove_items(self, source_field_name, target_field_name, *objs):
             # source_col_name: the PK colname in join_table for the source object
@@ -544,9 +551,21 @@ def _remove_items(self, source_field_name, target_field_name, *objs):
                     source_field_name: self._pk_val,
                     '%s__in' % target_field_name: old_ids
                 }).delete()
+                if self.reverse or source_field_name == self.source_field_name:
+                    # Don't send the signal when we are deleting the
+                    # duplicate data row for symmetrical reverse entries.
+                    signals.m2m_changed.send(sender=rel.through, action="remove",
+                        instance=self.instance, reverse=self.reverse,
+                        model=self.model, pk_set=old_ids)
 
         def _clear_items(self, source_field_name):
             # source_col_name: the PK colname in join_table for the source object
+            if self.reverse or source_field_name == self.source_field_name:
+                # Don't send the signal when we are clearing the
+                # duplicate data rows for symmetrical reverse entries.
+                signals.m2m_changed.send(sender=rel.through, action="clear",
+                    instance=self.instance, reverse=self.reverse,
+                    model=self.model, pk_set=None)
             self.through._default_manager.using(self.instance._state.db).filter(**{
                 source_field_name: self._pk_val
             }).delete()
@@ -579,7 +598,8 @@ def __get__(self, instance, instance_type=None):
             instance=instance,
             symmetrical=False,
             source_field_name=self.related.field.m2m_reverse_field_name(),
-            target_field_name=self.related.field.m2m_field_name()
+            target_field_name=self.related.field.m2m_field_name(),
+            reverse=True
         )
 
         return manager
@@ -596,6 +616,7 @@ def __set__(self, instance, value):
         manager.clear()
         manager.add(*value)
 
+
 class ReverseManyRelatedObjectsDescriptor(object):
     # This class provides the functionality that makes the related-object
     # managers available as attributes on a model class, for fields that have
@@ -629,7 +650,8 @@ def __get__(self, instance, instance_type=None):
             instance=instance,
             symmetrical=(self.field.rel.symmetrical and isinstance(instance, rel_model)),
             source_field_name=self.field.m2m_field_name(),
-            target_field_name=self.field.m2m_reverse_field_name()
+            target_field_name=self.field.m2m_reverse_field_name(),
+            reverse=False
         )
 
         return manager

django/db/models/signals.py

@@ -12,3 +12,5 @@
 post_delete = Signal(providing_args=["instance"])
 
 post_syncdb = Signal(providing_args=["class", "app", "created_models", "verbosity", "interactive"])
+
+m2m_changed = Signal(providing_args=["action", "instance", "reverse", "model", "pk_set"])

docs/ref/signals.txt

@@ -170,6 +170,123 @@ Arguments sent with this signal:
         Note that the object will no longer be in the database, so be very
         careful what you do with this instance.
 
+m2m_changed
+-----------
+
+.. data:: django.db.models.signals.m2m_changed
+   :module:
+
+Sent when a :class:`ManyToManyField` is changed on a model instance.
+Strictly speaking, this is not a model signal since it is sent by the
+:class:`ManyToManyField`, but since it complements the
+:data:`pre_save`/:data:`post_save` and :data:`pre_delete`/:data:`post_delete`
+when it comes to tracking changes to models, it is included here.
+
+Arguments sent with this signal:
+
+    ``sender``
+        The intermediate model class describing the :class:`ManyToManyField`.
+        This class is automatically created when a many-to-many field is
+        defined; it you can access it using the ``through`` attribute on the
+        many-to-many field.
+
+    ``instance``
+        The instance whose many-to-many relation is updated. This can be an
+        instance of the ``sender``, or of the class the :class:`ManyToManyField`
+        is related to.
+
+    ``action``
+        A string indicating the type of update that is done on the relation.
+        This can be one of the following:
+
+        ``"add"``
+            Sent *after* one or more objects are added to the relation
+        ``"remove"``
+            Sent *after* one or more objects are removed from the relation
+        ``"clear"``
+            Sent *before* the relation is cleared
+
+    ``reverse``
+    	Indicates which side of the relation is updated (i.e., if it is the
+    	forward or reverse relation that is being modified).
+
+    ``model``
+        The class of the objects that are added to, removed from or cleared
+        from the relation.
+
+    ``pk_set``
+        With the ``"add"`` and ``"remove"`` action, this is a list of
+        primary key values that have been added to or removed from the relation.
+
+        For the ``"clear"`` action, this is ``None``.
+
+For example, if a ``Pizza`` can have multiple ``Topping`` objects, modeled
+like this:
+
+.. code-block:: python
+
+    class Topping(models.Model):
+        # ...
+
+    class Pizza(models.Model):
+        # ...
+        toppings = models.ManyToManyField(Topping)
+
+If we would do something like this:
+
+.. code-block:: python
+
+    >>> p = Pizza.object.create(...)
+    >>> t = Topping.objects.create(...)
+    >>> p.toppings.add(t)
+
+the arguments sent to a :data:`m2m_changed` handler would be:
+
+    ==============  ============================================================
+    Argument        Value
+    ==============  ============================================================
+    ``sender``      ``Pizza.toppings.through`` (the intermediate m2m class)
+
+    ``instance``    ``p`` (the ``Pizza`` instance being modified)
+
+    ``action``      ``"add"``
+
+    ``reverse``     ``False`` (``Pizza`` contains the :class:`ManyToManyField`,
+                    so this call modifies the forward relation)
+
+    ``model``       ``Topping`` (the class of the objects added to the
+                    ``Pizza``)
+
+    ``pk_set``      ``[t.id]`` (since only ``Topping t`` was added to the relation)
+    ==============  ============================================================
+
+And if we would then do something like this:
+
+.. code-block:: python
+
+    >>> t.pizza_set.remove(p)
+
+the arguments sent to a :data:`m2m_changed` handler would be:
+
+    ==============  ============================================================
+    Argument        Value
+    ==============  ============================================================
+    ``sender``      ``Pizza.toppings.through`` (the intermediate m2m class)
+
+    ``instance``    ``t`` (the ``Topping`` instance being modified)
+
+    ``action``      ``"remove"``
+
+    ``reverse``     ``True`` (``Pizza`` contains the :class:`ManyToManyField`,
+                    so this call modifies the reverse relation)
+
+    ``model``       ``Pizza`` (the class of the objects removed from the
+                    ``Topping``)
+
+    ``pk_set``      ``[p.id]`` (since only ``Pizza p`` was removed from the
+                    relation)
+    ==============  ============================================================
+
 class_prepared
 --------------
 

docs/topics/signals.txt

@@ -29,6 +29,9 @@ notifications:
       Sent before or after a model's :meth:`~django.db.models.Model.delete`
       method is called.
 
+    * :data:`django.db.models.signals.m2m_changed`
+
+      Sent when a :class:`ManyToManyField` on a model is changed.
 
     * :data:`django.core.signals.request_started` &
       :data:`django.core.signals.request_finished`

tests/modeltests/m2m_signals/__init__.py

@@ -0,0 +1 @@
+