Fixed #7539, #13067 -- Added on_delete argument to ForeignKey to control cascade behavior. Also refactored deletion for efficiency and code clarity. Many thanks to Johannes Dollinger and Michael Glassford for extensive work on the patch, and to Alex Gaynor, Russell Keith-Magee, and Jacob Kaplan-Moss for review.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14507 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/core/management/validation.py

@@ -22,6 +22,7 @@ def get_validation_errors(outfile, app=None):
     from django.db import models, connection
     from django.db.models.loading import get_app_errors
     from django.db.models.fields.related import RelatedObject
+    from django.db.models.deletion import SET_NULL, SET_DEFAULT
 
     e = ModelErrorCollection(outfile)
 
@@ -85,6 +86,13 @@ def get_validation_errors(outfile, app=None):
             # Perform any backend-specific field validation.
             connection.validation.validate_field(e, opts, f)
 
+            # Check if the on_delete behavior is sane
+            if f.rel and hasattr(f.rel, 'on_delete'):
+                if f.rel.on_delete == SET_NULL and not f.null:
+                    e.add(opts, "'%s' specifies on_delete=SET_NULL, but cannot be null." % f.name)
+                elif f.rel.on_delete == SET_DEFAULT and not f.has_default():
+                    e.add(opts, "'%s' specifies on_delete=SET_DEFAULT, but has no default value." % f.name)
+
             # Check to see if the related field will clash with any existing
             # fields, m2m fields, m2m related objects or related objects
             if f.rel: