--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/parts/django/tests/modeltests/field_subclassing/fields.py	Sat Jan 08 11:20:57 2011 +0530
@@ -0,0 +1,74 @@
+from django.core.exceptions import FieldError
+from django.db import models
+from django.utils import simplejson as json
+from django.utils.encoding import force_unicode
+
+
+class Small(object):
+    """
+    A simple class to show that non-trivial Python objects can be used as
+    attributes.
+    """
+    def __init__(self, first, second):
+        self.first, self.second = first, second
+
+    def __unicode__(self):
+        return u'%s%s' % (force_unicode(self.first), force_unicode(self.second))
+
+    def __str__(self):
+        return unicode(self).encode('utf-8')
+
+class SmallField(models.Field):
+    """
+    Turns the "Small" class into a Django field. Because of the similarities
+    with normal character fields and the fact that Small.__unicode__ does
+    something sensible, we don't need to implement a lot here.
+    """
+    __metaclass__ = models.SubfieldBase
+
+    def __init__(self, *args, **kwargs):
+        kwargs['max_length'] = 2
+        super(SmallField, self).__init__(*args, **kwargs)
+
+    def get_internal_type(self):
+        return 'CharField'
+
+    def to_python(self, value):
+        if isinstance(value, Small):
+            return value
+        return Small(value[0], value[1])
+
+    def get_db_prep_save(self, value):
+        return unicode(value)
+
+    def get_prep_lookup(self, lookup_type, value):
+        if lookup_type == 'exact':
+            return force_unicode(value)
+        if lookup_type == 'in':
+            return [force_unicode(v) for v in value]
+        if lookup_type == 'isnull':
+            return []
+        raise TypeError('Invalid lookup type: %r' % lookup_type)
+
+class SmallerField(SmallField):
+    pass
+
+
+class JSONField(models.TextField):
+    __metaclass__ = models.SubfieldBase
+
+    description = ("JSONField automatically serializes and desializes values to "
+        "and from JSON.")
+
+    def to_python(self, value):
+        if not value:
+            return None
+
+        if isinstance(value, basestring):
+            value = json.loads(value)
+        return value
+
+    def get_db_prep_save(self, value):
+        if value is None:
+            return None
+        return json.dumps(value)