--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/parts/django/tests/modeltests/custom_pk/fields.py	Sat Jan 08 11:20:57 2011 +0530
@@ -0,0 +1,55 @@
+import random
+import string
+
+from django.db import models
+
+
+class MyWrapper(object):
+    def __init__(self, value):
+        self.value = value
+
+    def __repr__(self):
+        return "<%s: %s>" % (self.__class__.__name__, self.value)
+
+    def __unicode__(self):
+        return self.value
+
+    def __eq__(self, other):
+        if isinstance(other, self.__class__):
+            return self.value == other.value
+        return self.value == other
+
+class MyAutoField(models.CharField):
+    __metaclass__ = models.SubfieldBase
+
+    def __init__(self, *args, **kwargs):
+        kwargs['max_length'] = 10
+        super(MyAutoField, self).__init__(*args, **kwargs)
+
+    def pre_save(self, instance, add):
+        value = getattr(instance, self.attname, None)
+        if not value:
+            value = MyWrapper(''.join(random.sample(string.lowercase, 10)))
+            setattr(instance, self.attname, value)
+        return value
+
+    def to_python(self, value):
+        if not value:
+            return
+        if not isinstance(value, MyWrapper):
+            value = MyWrapper(value)
+        return value
+
+    def get_db_prep_save(self, value):
+        if not value:
+            return
+        if isinstance(value, MyWrapper):
+            return unicode(value)
+        return value
+
+    def get_db_prep_value(self, value):
+        if not value:
+            return
+        if isinstance(value, MyWrapper):
+            return unicode(value)
+        return value