[1.0.X] Changed r10672 to not falsely error out when using generic in…

…lines.

The bug was picked up by the tests already, but only if run against a
backend that supports referential integrity.

Backport of r10732 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@10736 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/contrib/admin/validation.py

@@ -140,11 +140,11 @@ def validate_inline(cls, parent, parent_model):
 
     # exclude
     if hasattr(cls, 'exclude') and cls.exclude:
-        fk_name = _get_foreign_key(parent_model, cls.model).name
-        if fk_name in cls.exclude:
+        fk = _get_foreign_key(parent_model, cls.model, can_fail=True)
+        if fk and fk.name in cls.exclude:
             raise ImproperlyConfigured("%s cannot exclude the field "
                     "'%s' - this is the foreign key to the parent model "
-                    "%s." % (cls.__name__, fk_name, parent_model.__name__))
+                    "%s." % (cls.__name__, fk.name, parent_model.__name__))
 
 def validate_base(cls, model):
     opts = model._meta

django/forms/models.py

@@ -727,10 +727,13 @@ def get_unique_error_message(self, unique_check):
         unique_check = [field for field in unique_check if field != self.fk.name]
         return super(BaseInlineFormSet, self).get_unique_error_message(unique_check)
 
-def _get_foreign_key(parent_model, model, fk_name=None):
+def _get_foreign_key(parent_model, model, fk_name=None, can_fail=False):
     """
-    Finds and returns the ForeignKey from model to parent if there is one.
-    If fk_name is provided, assume it is the name of the ForeignKey field.
+    Finds and returns the ForeignKey from model to parent if there is one
+    (returns None if can_fail is True and no such field exists). If fk_name is
+    provided, assume it is the name of the ForeignKey field. Unles can_fail is
+    True, an exception is raised if there is no ForeignKey from model to
+    parent_model.
     """
     # avoid circular import
     from django.db.models import ForeignKey
@@ -756,6 +759,8 @@ def _get_foreign_key(parent_model, model, fk_name=None):
         if len(fks_to_parent) == 1:
             fk = fks_to_parent[0]
         elif len(fks_to_parent) == 0:
+            if can_fail:
+                return
             raise Exception("%s has no ForeignKey to %s" % (model, parent_model))
         else:
             raise Exception("%s has more than 1 ForeignKey to %s" % (model, parent_model))