Ticket #24325: 24325.diff

docs/releases/1.8.txt

@@ -710 +710 @@
     ...
     ValueError: Cannot assign "<Author: John>": "Author" instance isn't saved in the database.
 
+Accessing foreign keys in ``ModelForm.save()``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In older versions, you could access foreign keys in ``ModelForm.save()`` when
+adding new instances. For example, given ``Book`` with a ``ForeignKey`` to
+``Author``::
+
+    class BookForm(forms.ModelForm):
+        def save(self, *args, **kwargs):
+            book = super(BookForm, self).save(*args, **kwargs)
+            book.title = "%s by %s" % (book.title, book.author.name)
+            return book
+
+This is no longer possible because accessing the foreign key (``book.author``
+in the example) will raise ``RelatedObjectDoesNotExist``. This change was
+necessary to avoid assigning unsaved objects to relations (as described in the
+previous section).
+
+To adapt the above example, you could replace ``book.author.name`` with
+``self.cleaned_data['author'].name``.
+
 Management commands that only accept positional arguments
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~