django-mixins.py

from django.db import models
from django.contrib.contenttypes import generic
from django.contrib.contenttypes.models import ContentType


class GenericLinkedModel(models.Model):
    """
    Abstract base model that allows for an object to be linked (foreign-keyed)
    to various models. Useful example: Comments or tags for different types of
    objects.

    Example Usage:
    ==============
    
    from django.contrib.contenttypes import generic
    ...

    class Comment(GenericLinkedModel):
        text = models.Charfield(max_length=500)
        ...

    class Post(models.Model):
        comments = generic.GenericRelation(Comment)
        ...

    """

    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField()
    content_object = generic.GenericForeignKey('content_type', 'object_id')

    class Meta:
        abstract = True