Modified [7112] to make things behave more in line with Python subclassing when subclassing ModelForms.

Meta can now be subclassed and changes on the child model affect the fields
list. Also removed a block of error checking, since it's harder to mess up in
unexpected ways now (e.g. you can't change the model and get the entirely wrong
fields list), so it was a level of overkill.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@7115 bcc190cf-cafb-0310-a4f2-bffc1f526a37

1 files changed, 10 insertions, 12 deletions

diff --git a/docs/modelforms.txt b/docs/modelforms.txt
index ec0ecf40cc..b9f0d88165 100644
--- a/docs/modelforms.txt
+++ b/docs/modelforms.txt
@@ -335,14 +335,19 @@ models. For example, using the previous ``ArticleForm`` class::
 This creates a form that behaves identically to ``ArticleForm``, except there
 is some extra validation and cleaning for the ``pub_date`` field.
 
+You can also subclass the parent's ``Meta`` inner class if you want to change
+the ``Meta.fields`` or ``Meta.excludes`` lists::
+
+    >>> class RestrictedArticleForm(EnhancedArticleForm):
+    ...     class Meta(ArticleForm.Meta):
+    ...         exclude = ['body']
+
+This adds in the extra method from the ``EnhancedArticleForm`` and modifies
+the original ``ArticleForm.Meta`` to remove one field.
+
 There are a couple of things to note, however. Most of these won't normally be
 of concern unless you are trying to do something tricky with subclassing.
 
- * All the fields from the parent classes will appear in the child
-   ``ModelForm``. This means you cannot change a parent's ``Meta.exclude``
-   attribute, for example, and except it to have an effect, since the field is
-   already part of the field list in the parent class.
-
  * Normal Python name resolution rules apply. If you have multiple base
    classes that declare a ``Meta`` inner class, only the first one will be
    used.  This means the child's ``Meta``, if it exists, otherwise the
@@ -351,10 +356,3 @@ of concern unless you are trying to do something tricky with subclassing.
  * For technical reasons, you cannot have a subclass that is inherited from
    both a ``ModelForm`` and a ``Form`` simultaneously.
 
-Because of the "child inherits all fields from parents" behaviour, you
-shouldn't try to declare model fields in multiple classes (parent and child).
-Instead, declare all the model-related stuff in one class and use inheritance
-to add "extra" non-model fields and methods to the final result. Whether you
-put the "extra" functions in the parent class or the child class will depend
-on how you intend to reuse them.
-