Ticket #1745: m2m_requires_pk_val.patch

django/db/models/fields/related.py

@@ -239 +239 @@
             self.join_table = join_table
             self.source_col_name = source_col_name
             self.target_col_name = target_col_name
-            if instance:
-                self._pk_val = self.instance._get_pk_val()
+            self._pk_val = self.instance._get_pk_val()
+            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." % model)
 
         def get_query_set(self):
             return superclass.get_query_set(self).filter(**(self.core_filters))

tests/modeltests/many_to_many/models.py

@@ -110 +110 @@
 >>> a2.delete()
 >>> Article.objects.all()
 [Django lets you build Web apps easily]
->>> p1.article_set.all()
-[Django lets you build Web apps easily]
+>>> p2.article_set.all()
+[]
 
 # Adding via the 'other' end of an m2m
 >>> a4 = Article(headline='NASA finds intelligent life on Earth')