Fixed django#9475 -- allow add(), create(), etc for m2m with through

django/db/models/fields/related_descriptors.py

@@ -906,32 +906,20 @@ def get_prefetch_queryset(self, instances, queryset=None):
                 False,
             )
 
-        def add(self, *objs):
-            if not rel.through._meta.auto_created:
-                opts = self.through._meta
-                raise AttributeError(
-                    "Cannot use add() on a ManyToManyField which specifies an "
-                    "intermediary model. Use %s.%s's Manager instead." %
-                    (opts.app_label, opts.object_name)
-                )
+        def add(self, *objs, through_defaults=None):
             self._remove_prefetched_objects()
             db = router.db_for_write(self.through, instance=self.instance)
             with transaction.atomic(using=db, savepoint=False):
-                self._add_items(self.source_field_name, self.target_field_name, *objs)
+                self._add_items(
+                    self.source_field_name, self.target_field_name, *objs, through_defaults=through_defaults)
 
                 # 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_field_name, self.source_field_name, *objs)
+                    self._add_items(
+                        self.target_field_name, self.source_field_name, *objs, through_defaults=through_defaults)
         add.alters_data = True
 
         def remove(self, *objs):
-            if not rel.through._meta.auto_created:
-                opts = self.through._meta
-                raise AttributeError(
-                    "Cannot use remove() on a ManyToManyField which specifies "
-                    "an intermediary model. Use %s.%s's Manager instead." %
-                    (opts.app_label, opts.object_name)
-                )
             self._remove_prefetched_objects()
             self._remove_items(self.source_field_name, self.target_field_name, *objs)
         remove.alters_data = True
@@ -955,15 +943,7 @@ def clear(self):
                 )
         clear.alters_data = True
 
-        def set(self, objs, *, clear=False):
-            if not rel.through._meta.auto_created:
-                opts = self.through._meta
-                raise AttributeError(
-                    "Cannot set values on a ManyToManyField which specifies an "
-                    "intermediary model. Use %s.%s's Manager instead." %
-                    (opts.app_label, opts.object_name)
-                )
-
+        def set(self, objs, *, clear=False, through_defaults=None):
             # Force evaluation of `objs` in case it's a queryset whose value
             # could be affected by `manager.clear()`. Refs #19816.
             objs = tuple(objs)
@@ -972,7 +952,7 @@ def set(self, objs, *, clear=False):
             with transaction.atomic(using=db, savepoint=False):
                 if clear:
                     self.clear()
-                    self.add(*objs)
+                    self.add(*objs, through_defaults=through_defaults)
                 else:
                     old_ids = set(self.using(db).values_list(self.target_field.target_field.attname, flat=True))
 
@@ -988,49 +968,41 @@ def set(self, objs, *, clear=False):
                             new_objs.append(obj)
 
                     self.remove(*old_ids)
-                    self.add(*new_objs)
+                    self.add(*new_objs, through_defaults=through_defaults)
         set.alters_data = True
 
-        def create(self, **kwargs):
-            # This check needs to be done here, since we can't later remove this
-            # from the method lookup table, as we do with add and remove.
-            if not self.through._meta.auto_created:
-                opts = self.through._meta
-                raise AttributeError(
-                    "Cannot use create() on a ManyToManyField which specifies "
-                    "an intermediary model. Use %s.%s's Manager instead." %
-                    (opts.app_label, opts.object_name)
-                )
+        def create(self, through_defaults=None, **kwargs):
             db = router.db_for_write(self.instance.__class__, instance=self.instance)
             new_obj = super(ManyRelatedManager, self.db_manager(db)).create(**kwargs)
-            self.add(new_obj)
+            self.add(new_obj, through_defaults=through_defaults)
             return new_obj
         create.alters_data = True
 
-        def get_or_create(self, **kwargs):
+        def get_or_create(self, through_defaults=None, **kwargs):
             db = router.db_for_write(self.instance.__class__, instance=self.instance)
             obj, created = super(ManyRelatedManager, self.db_manager(db)).get_or_create(**kwargs)
             # We only need to add() if created because if we got an object back
             # from get() then the relationship already exists.
             if created:
-                self.add(obj)
+                self.add(obj, through_defaults=through_defaults)
             return obj, created
         get_or_create.alters_data = True
 
-        def update_or_create(self, **kwargs):
+        def update_or_create(self, through_defaults=None, **kwargs):
             db = router.db_for_write(self.instance.__class__, instance=self.instance)
             obj, created = super(ManyRelatedManager, self.db_manager(db)).update_or_create(**kwargs)
             # We only need to add() if created because if we got an object back
             # from get() then the relationship already exists.
             if created:
-                self.add(obj)
+                self.add(obj, through_defaults=through_defaults)
             return obj, created
         update_or_create.alters_data = True
 
-        def _add_items(self, source_field_name, target_field_name, *objs):
+        def _add_items(self, source_field_name, target_field_name, *objs, through_defaults=None):
             # source_field_name: the PK fieldname in join table for the source object
             # target_field_name: the PK fieldname in join table for the target object
             # *objs - objects to add. Either object instances, or primary keys of object instances.
+            through_defaults = through_defaults or {}
 
             # If there aren't any objects, there is nothing to do.
             from django.db.models import Model
@@ -1080,10 +1052,10 @@ def _add_items(self, source_field_name, target_field_name, *objs):
 
                     # Add the ones that aren't there already
                     self.through._default_manager.using(db).bulk_create([
-                        self.through(**{
+                        self.through(**dict(through_defaults, **{
                             '%s_id' % source_field_name: self.related_val[0],
                             '%s_id' % target_field_name: obj_id,
-                        })
+                        }))
                         for obj_id in new_ids
                     ])
 

docs/ref/models/relations.txt

@@ -36,7 +36,7 @@ Related objects reference
       In this example, the methods below will be available both on
       ``topping.pizza_set`` and on ``pizza.toppings``.
 
-    .. method:: add(*objs, bulk=True)
+    .. method:: add(*objs, bulk=True, through_defaults=None)
 
         Adds the specified model objects to the related object set.
 
@@ -62,7 +62,14 @@ Related objects reference
         some custom logic when a relationship is created, listen to the
         :data:`~django.db.models.signals.m2m_changed` signal.
 
-    .. method:: create(**kwargs)
+        The ``through_defaults`` argument can be used to specify values for
+        the new :ref:`an intermediate model <intermediary-manytomany>` instance.
+
+       .. versionchanged:: 2.1
+
+            The ``through_defaults`` argument was added.
+
+    .. method:: create(through_defaults=None, **kwargs)
 
         Creates a new object, saves it and puts it in the related object set.
         Returns the newly created object::
@@ -92,6 +99,13 @@ Related objects reference
         parameter ``blog`` to ``create()``. Django figures out that the new
         ``Entry`` object's ``blog`` field should be set to ``b``.
 
+        The ``through_defaults`` argument can be used to specify values for
+        the new :ref:`an intermediate model <intermediary-manytomany>` instance.
+
+       .. versionchanged:: 2.1
+
+            The ``through_defaults`` argument was added.
+
     .. method:: remove(*objs)
 
         Removes the specified model objects from the related object set::
@@ -125,6 +139,11 @@ Related objects reference
         :data:`~django.db.models.signals.post_save` signals and comes at the
         expense of performance.
 
+       .. versionchanged:: 2.1
+
+            The ``remove()`` method is now allowed on relationships with
+            custom intermediate models.
+
     .. method:: clear()
 
         Removes all objects from the related object set::
@@ -139,7 +158,7 @@ Related objects reference
         :class:`~django.db.models.ForeignKey`\s where ``null=True`` and it also
         accepts the ``bulk`` keyword argument.
 
-    .. method:: set(objs, bulk=True, clear=False)
+    .. method:: set(objs, bulk=True, clear=False, through_defaults=None)
 
         Replace the set of related objects::
 
@@ -158,18 +177,20 @@ Related objects reference
         race conditions. For instance, new objects may be added to the database
         in between the call to ``clear()`` and the call to ``add()``.
 
+        The ``through_defaults`` argument can be used to specify values for
+        new :ref:`an intermediate model <intermediary-manytomany>` instances.
+
     .. note::
 
        Note that ``add()``, ``create()``, ``remove()``, ``clear()``, and
        ``set()`` all apply database changes immediately for all types of
        related fields. In other words, there is no need to call ``save()``
        on either end of the relationship.
 
-       Also, if you are using :ref:`an intermediate model
-       <intermediary-manytomany>` for a many-to-many relationship, then the
-       ``add()``, ``create()``, ``remove()``, and ``set()`` methods are
-       disabled.
-
        If you use :meth:`~django.db.models.query.QuerySet.prefetch_related`,
        the ``add()``, ``remove()``, ``clear()``, and ``set()`` methods clear
        the prefetched cache.
+
+       .. versionchanged:: 2.1
+
+            The ``through_defaults`` argument was added.

docs/releases/2.1.txt

@@ -164,6 +164,12 @@ Migrations
 Models
 ~~~~~~
 
+* The ``add()``, ``create()``, ``get_or_create()``, ``update_or_create()``,
+  ``set()``, and ``remove()`` methods are now allowed on many-to-many
+  relationships with custom intermediate models. There is a
+  ``through_defaults`` argument for specifying values for new intermediate
+  models.
+
 * Models can now use ``__init_subclass__()`` from :pep:`487`.
 
 * A ``BinaryField`` may now be set to ``editable=True`` if you wish to include

docs/topics/db/examples/many_to_many.txt

@@ -34,10 +34,7 @@ objects, and a ``Publication`` has multiple ``Article`` objects:
             ordering = ('headline',)
 
 What follows are examples of operations that can be performed using the Python
-API facilities. Note that if you are using :ref:`an intermediate model
-<intermediary-manytomany>` for a many-to-many relationship, some of the related
-manager's methods are disabled, so some of these examples won't work with such
-models.
+API facilities.
 
 Create a couple of ``Publications``::
 

docs/topics/db/models.txt

@@ -511,37 +511,34 @@ the intermediate model::
     >>> beatles.members.all()
     <QuerySet [<Person: Ringo Starr>, <Person: Paul McCartney>]>
 
-Unlike normal many-to-many fields, you *can't* use ``add()``, ``create()``,
-or ``set()`` to create relationships::
+You can also use ``add()``, ``create()``, or ``set()`` to create relationships,
+as long as your specify ``through_defaults`` for any required fields::
 
     >>> # The following statements will not work
-    >>> beatles.members.add(john)
-    >>> beatles.members.create(name="George Harrison")
-    >>> beatles.members.set([john, paul, ringo, george])
-
-Why? You can't just create a relationship between a ``Person`` and a ``Group``
-- you need to specify all the detail for the relationship required by the
-``Membership`` model. The simple ``add``, ``create`` and assignment calls
-don't provide a way to specify this extra detail. As a result, they are
-disabled for many-to-many relationships that use an intermediate model.
-The only way to create this type of relationship is to create instances of the
-intermediate model.
-
-The :meth:`~django.db.models.fields.related.RelatedManager.remove` method is
-disabled for similar reasons. For example, if the custom through table defined
-by the intermediate model does not enforce uniqueness on the
-``(model1, model2)`` pair, a ``remove()`` call would not provide enough
-information as to which intermediate model instance should be deleted::
+    >>> beatles.members.add(john, through_defaults={'date_joined': date(1960, 8, 1)})
+    >>> beatles.members.create(name="George Harrison", through_defaults={'date_joined': date(1960, 8, 1)})
+    >>> beatles.members.set([john, paul, ringo, george], through_defaults={'date_joined': date(1960, 8, 1)})
+
+The simple ``add``, ``create`` and ``set`` calls don't provide a way to
+specify different details for different objects. You may prefer to create
+instances of the intermediate model directly instead.
+
+If the custom through table defined by the intermediate model does not enforce
+uniqueness on the ``(model1, model2)`` pair, allowing multiple values, the
+:meth:`~django.db.models.fields.related.RelatedManager.remove` call will
+remove all intermediate model instances::
 
     >>> Membership.objects.create(person=ringo, group=beatles,
     ...     date_joined=date(1968, 9, 4),
     ...     invite_reason="You've been gone for a month and we miss you.")
     >>> beatles.members.all()
     <QuerySet [<Person: Ringo Starr>, <Person: Paul McCartney>, <Person: Ringo Starr>]>
-    >>> # This will not work because it cannot tell which membership to remove
+    >>> # This deletes both of the intermediate model instances for Ringo Starr
     >>> beatles.members.remove(ringo)
+    >>> beatles.members.all()
+    <QuerySet [<Person: Paul McCartney>]>
 
-However, the :meth:`~django.db.models.fields.related.RelatedManager.clear`
+The :meth:`~django.db.models.fields.related.RelatedManager.clear`
 method can be used to remove all many-to-many relationships for an instance::
 
     >>> # Beatles have broken up
@@ -550,10 +547,9 @@ method can be used to remove all many-to-many relationships for an instance::
     >>> Membership.objects.all()
     <QuerySet []>
 
-Once you have established the many-to-many relationships by creating instances
-of your intermediate model, you can issue queries. Just as with normal
-many-to-many relationships, you can query using the attributes of the
-many-to-many-related model::
+Once you have established the many-to-many relationships, you can issue
+queries. Just as with normal many-to-many relationships, you can query using
+the attributes of the many-to-many-related model::
 
     # Find all the groups with a member whose name starts with 'Paul'
     >>> Group.objects.filter(members__name__startswith='Paul')

tests/m2m_through/models.py

@@ -23,6 +23,7 @@ class Group(models.Model):
         through='TestNoDefaultsOrNulls',
         related_name="testnodefaultsnonulls",
     )
+    required_through = models.ManyToManyField(Person, through='RequiredThrough', related_name='required_through')
 
     class Meta:
         ordering = ('name',)
@@ -69,6 +70,12 @@ class TestNoDefaultsOrNulls(models.Model):
     nodefaultnonull = models.CharField(max_length=5)
 
 
+class RequiredThrough(models.Model):
+    person = models.ForeignKey(Person, models.CASCADE)
+    group = models.ForeignKey(Group, models.CASCADE)
+    required = models.IntegerField()
+
+
 class PersonSelfRefM2M(models.Model):
     name = models.CharField(max_length=5)
     friends = models.ManyToManyField('self', through="Friendship", symmetrical=False)