django-m2m.patch

diff --git a/django/db/models/fields/related.py b/django/db/models/fields/related.py
index 529898e..dcac719 100644
--- a/django/db/models/fields/related.py
+++ b/django/db/models/fields/related.py
@@ -405,8 +405,9 @@ def create_many_related_manager(superclass, through=False):
     """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):
+        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, reverse=False):
             super(ManyRelatedManager, self).__init__()
             self.core_filters = core_filters
             self.model = model
@@ -417,6 +418,8 @@ def create_many_related_manager(superclass, through=False):
             self.target_col_name = target_col_name
             self.through = through
             self._pk_val = self.instance._get_pk_val()
+            self.field_name = field_name
+            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__)
 
@@ -498,10 +501,22 @@ def create_many_related_manager(superclass, through=False):
                 existing_ids = set([row[0] for row in cursor.fetchall()])
 
                 # Add the ones that aren't there already
-                for obj_id in (new_ids - existing_ids):
+                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]
+                if self.reverse:
+                    sender = self.model
+                else:
+                    sender = self.instance.__class__
+                signals.m2m_changed.send(sender=sender, action='add',
+                    instance=self.instance, model=self.model, 
+                    reverse=self.reverse, field_name=self.field_name, 
+                    objects=added_objs)
                 transaction.commit_unless_managed()
 
         def _remove_items(self, source_col_name, target_col_name, *objs):
@@ -524,9 +539,24 @@ def create_many_related_manager(superclass, through=False):
                     (self.join_table, source_col_name,
                     target_col_name, ",".join(['%s'] * len(old_ids))),
                     [self._pk_val] + list(old_ids))
+                if self.reverse:
+                    sender = self.model
+                else:
+                    sender = self.instance.__class__
+                signals.m2m_changed.send(sender=sender, action="remove",
+                    instance=self.instance, model=self.model,
+                    reverse=self.reverse, field_name=self.field_name, 
+                    objects=list(objs))
                 transaction.commit_unless_managed()
 
         def _clear_items(self, source_col_name):
+            if self.reverse:
+                    sender = self.model
+            else:
+                    sender = self.instance.__class__
+            signals.m2m_changed.send(sender=sender, action="clear",
+                instance=self.instance, model=self.model, reverse=self.reverse, 
+                field_name=self.field_name, objects=None)
             # source_col_name: the PK colname in join_table for the source object
             cursor = connection.cursor()
             cursor.execute("DELETE FROM %s WHERE %s = %%s" % \
@@ -564,7 +594,9 @@ class ManyRelatedObjectsDescriptor(object):
             symmetrical=False,
             join_table=qn(self.related.field.m2m_db_table()),
             source_col_name=qn(self.related.field.m2m_reverse_name()),
-            target_col_name=qn(self.related.field.m2m_column_name())
+            target_col_name=qn(self.related.field.m2m_column_name()),
+            field_name=self.related.field.name,
+            reverse=True
         )
 
         return manager
@@ -609,7 +641,9 @@ class ReverseManyRelatedObjectsDescriptor(object):
             symmetrical=(self.field.rel.symmetrical and isinstance(instance, rel_model)),
             join_table=qn(self.field.m2m_db_table()),
             source_col_name=qn(self.field.m2m_column_name()),
-            target_col_name=qn(self.field.m2m_reverse_name())
+            target_col_name=qn(self.field.m2m_reverse_name()),
+            field_name=self.field.name,
+            reverse=False
         )
 
         return manager
diff --git a/django/db/models/signals.py b/django/db/models/signals.py
index 0455336..d5457d3 100644
--- a/django/db/models/signals.py
+++ b/django/db/models/signals.py
@@ -12,3 +12,5 @@ pre_delete = Signal(providing_args=["instance"])
 post_delete = Signal(providing_args=["instance"])
 
 post_syncdb = Signal(providing_args=["class", "app", "created_models", "verbosity", "interactive"])
+
+m2m_changed = Signal(providing_args=["instance", "action", "model", "field_name", "reverse", "objects"])
diff --git a/docs/ref/signals.txt b/docs/ref/signals.txt
index cc203f1..32b2e6f 100644
--- a/docs/ref/signals.txt
+++ b/docs/ref/signals.txt
@@ -170,6 +170,139 @@ 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 model class containing the :class:`ManyToManyField`.
+
+    ``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.
+        
+    ``model``
+        The class of the objects that are added to, removed from or cleared 
+        from the relation.
+        
+    ``field_name``
+        The name of the :class:`ManyToManyField` in the ``sender`` class.
+        This can be used to identify which relation has changed 
+        when multiple many-to-many relations to the same model 
+        exist in ``sender``.
+        
+    ``reverse``
+    	Indicates which side of the relation is updated.
+    	It is ``False`` for updates on an instance of the ``sender`` and
+        ``True`` for updates on an instance of the related class.
+        
+    ``objects``
+        With the ``"add"`` and ``"remove"`` action, this is a list of
+        objects that have been added to or removed from the relation.
+        The class of these objects is given in the ``model`` argument.
+        
+        For the ``"clear"`` action, this is ``None`` .
+        
+        Note that if you pass primary keys to the ``add`` or ``remove`` method
+        of a relation, ``objects`` will contain primary keys, not instances.
+        Also note that if you pass objects to the ``add`` method that are 
+        already in the relation, they will not be in the ``objects`` list.
+        (This doesn't apply to ``remove``.)
+        
+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`` (the class containing the field)
+
+    ``instance``    ``p`` (the ``Pizza`` instance being modified)
+
+    ``action``      ``"add"`` since the ``add`` method was called
+    
+    ``model``       ``Topping`` (the class of the objects added to the
+                    ``Pizza``)
+    
+    ``reverse``     ``False`` (since ``Pizza`` contains the 
+                    :class:`ManyToManyField`)
+    
+    ``field_name``  ``"topping"`` (the name of the :class:`ManyToManyField`)
+    
+    ``objects``     ``[t]`` (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`` (the class containing the field)
+
+    ``instance``    ``t`` (the ``Topping`` instance being modified)
+
+    ``action``      ``"remove"`` since the ``remove`` method was called
+    
+    ``model``       ``Pizza`` (the class of the objects removed from the 
+                    ``Topping``)
+    
+    ``reverse``     ``True`` (since ``Pizza`` contains the
+                    :class:`ManyToManyField` but the relation is modified
+                    through ``Topping``)
+    
+    ``field_name``  ``"topping"`` (the name of the :class:`ManyToManyField`)
+    
+    ``objects``     ``[p]`` (since only ``Pizza p`` was removed from the 
+                    relation)
+    ==============  ============================================================
+
 class_prepared
 --------------
 
diff --git a/docs/topics/signals.txt b/docs/topics/signals.txt
index 6f66b03..3539093 100644
--- a/docs/topics/signals.txt
+++ b/docs/topics/signals.txt
@@ -28,7 +28,10 @@ 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`