[1.0.X] Fixed #9649 -- Better error handling in model creation.

Previously, you could explicitly assign None to a non-null ForeignKey
(or other) field when creating the model (Child(parent=None), etc). We
now throw an exception when you do that, which matches the behaviour
when you assign None to the attribute after creation.

Thanks to ales.zoulek@gmail.com and ondrej.kohout@gmail.com for some
analysis of this problem.

Backport of r9983 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@9984 bcc190cf-cafb-0310-a4f2-bffc1f526a37

2 files changed, 19 insertions, 7 deletions

diff --git a/django/db/models/base.py b/django/db/models/base.py
index 50a701dce2..e704db2918 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -224,12 +224,13 @@ class Model(object):
         # keywords, or default.
 
         for field in fields_iter:
-            rel_obj = None
+            is_related_object = False
             if kwargs:
                 if isinstance(field.rel, ManyToOneRel):
                     try:
                         # Assume object instance was passed in.
                         rel_obj = kwargs.pop(field.name)
+                        is_related_object = True
                     except KeyError:
                         try:
                             # Object instance wasn't passed in -- must be an ID.
@@ -245,11 +246,11 @@ class Model(object):
                     val = kwargs.pop(field.attname, field.get_default())
             else:
                 val = field.get_default()
-            # If we got passed a related instance, set it using the field.name
-            # instead of field.attname (e.g. "user" instead of "user_id") so
-            # that the object gets properly cached (and type checked) by the
-            # RelatedObjectDescriptor.
-            if rel_obj:
+            if is_related_object:
+                # If we are passed a related instance, set it using the
+                # field.name instead of field.attname (e.g. "user" instead of
+                # "user_id") so that the object gets properly cached (and type
+                # checked) by the RelatedObjectDescriptor.
                 setattr(self, field.name, rel_obj)
             else:
                 setattr(self, field.attname, val)
diff --git a/tests/regressiontests/many_to_one_regress/models.py b/tests/regressiontests/many_to_one_regress/models.py
index 2039bd5ddf..3f35bef62c 100644
--- a/tests/regressiontests/many_to_one_regress/models.py
+++ b/tests/regressiontests/many_to_one_regress/models.py
@@ -1,5 +1,5 @@
 """
-Regression tests for a few FK bugs: #1578, #6886
+Regression tests for a few ForeignKey bugs.
 """
 
 from django.db import models
@@ -106,6 +106,17 @@ Traceback (most recent call last):
     ...
 ValueError: Cannot assign "<First: First object>": "Child.parent" must be a "Parent" instance.
 
+# Nor can you explicitly assign None to Child.parent during object creation
+# (regression for #9649).
+>>> Child(name='xyzzy', parent=None)
+Traceback (most recent call last):
+    ...
+ValueError: Cannot assign None: "Child.parent" does not allow null values.
+>>> Child.objects.create(name='xyzzy', parent=None)
+Traceback (most recent call last):
+    ...
+ValueError: Cannot assign None: "Child.parent" does not allow null values.
+
 # Creation using keyword argument should cache the related object.
 >>> p = Parent.objects.get(name="Parent")
 >>> c = Child(parent=p)