Django snippets

# -*- coding: UTF-8 -*-

from django.db import models
from datetime import datetime

class FullHistory(models.Model):
    """ 
    Issues: Unique fields don't work (multiple versions of the same row may need to have the same value)
    """
    date_created     = models.DateTimeField(default=datetime.now, editable=False)
    date_updated     = models.DateTimeField(default=datetime.now, editable=False)

    class Meta:
        abstract = True
        ordering = ('date_updated',)

    def __init__(self, *args, **kwargs):
        # History classes must end in 'History', others must not.
        if self.__class__.__name__.endswith('History'):
            self._history_class = True
        else:
            self._history_class = False
        super(FullHistory, self).__init__(*args, **kwargs)


    def save(self, *args, **kwargs):
        if self._history_class:
            self._save_history_instance()
        else:
            self._save_non_history_instance()

        super(FullHistory, self).save(*args, **kwargs)

    def _save_history_instance(self):
        """ Save method for a History object.
        """
        # This updated instance must become a new object, 
        # no updating is possible for history classes
        self.id = None

    def _save_non_history_instance(self):
        """ Save method for a non-History object.
        """
        # Duplicate and reassign parent.
        for model, field in self._meta.parents.items():
            if getattr(self, '%s_id' % field.name) is not None:
                rel_obj = getattr(self, field.name)
                rel_obj.id = None
                rel_obj.save()
                setattr(self, '%s_id' % field.name, rel_obj.id)

        # Set the new update time on the non-archived version
        self.date_updated = datetime.now()

    def delete(self):
        # Only delete if this is not a "history" version
        if not self._history_class:
            self.save()
            super(FullHistory, self).delete()