[soc2009/model-validation] A few words on validation methods on models

git-svn-id: http://code.djangoproject.com/svn/django/branches/soc2009/model-validation@11439 bcc190cf-cafb-0310-a4f2-bffc1f526a37

docs/ref/models/instances.txt

@@ -27,6 +27,30 @@ The keyword arguments are simply the names of the fields you've defined on your
 model. Note that instantiating a model in no way touches your database; for
 that, you need to ``save()``.
 
+Validating objects
+==================
+
+.. versionadded:: 1.2
+
+To validate your model, just call it's ``clean()`` method:
+
+.. method:: Model.clean([exclude=[]])
+
+The optional ``exclude`` argument can contain a list of field names that should
+be omitted when validating. This method raises ``ValidationError`` containing a
+message dict with errors from all fields.
+
+To add your own validation logic, override the supplied ``validate()`` method:
+
+.. method:: Model.validate()
+
+The ``validate()`` method on ``Model`` by default checks for uniqueness of
+fields and group of fields that are declared to be unique so remember to call
+``super.validate()`` if you want this validation to run.
+
+Any ``ValidationError`` raised in this method will be propagated in the
+``message_dict`` under ``NON_FIELD_ERRORS``.
+
 Saving objects
 ==============