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