Fixed #8209: ModelForms now validate unique constraints. Alex Gaynor did much of this work, and Brian Rosner helped as well.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@8805 bcc190cf-cafb-0310-a4f2-bffc1f526a37

docs/topics/forms/modelforms.txt

@@ -338,6 +338,16 @@ parameter when declaring the form field::
    ...     class Meta:
    ...         model = Article
 
+Overriding the clean() method
+-----------------------------
+
+You can overide the ``clean()`` method on a model form to provide additional
+validation in the same way you can on a normal form.  However, by default the
+``clean()`` method validates the uniqueness of fields that are marked as unique
+on the model, and those marked as unque_together, if you would like to overide
+the ``clean()`` method and maintain the default validation you must call the
+parent class's ``clean()`` method.
+
 Form inheritance
 ----------------
 
@@ -500,4 +510,4 @@ books of a specific author. Here is how you could accomplish this::
     >>> from django.forms.models import inlineformset_factory
     >>> BookFormSet = inlineformset_factory(Author, Book)
     >>> author = Author.objects.get(name=u'Orson Scott Card')
-    >>> formset = BookFormSet(instance=author)
+    >>> formset = BookFormSet(instance=author)