class Post(models.Model):
    text = models.TextField(u"Post")

class Image(models.Model):
    image = models.ImageField(u"Image")

class Video(models.Model):
    url = models.URLField(u"Video") 

class Item(models.Model):
    CONTENT_TYPE_CHOICES = (
        (ContentType.objects.get_for_model(Post), 'Post'),
        (ContentType.objects.get_for_model(Image),'Image'),
        (ContentType.objects.get_for_model(Video),'Video')
    )
    content_type    = models.ForeignKey(ContentType,choices=CONTENT_TYPE_CHOICES)
    object_id       = models.PositiveIntegerField()
    content_object  = generic.GenericForeignKey("content_type", "object_id")
    article         = models.ForeignKey(Article, related_name='items')

class Article(models.Model):
    title       = models.CharField(u"Title", max_length=255)
    link        = models.URLField(u"Adres URL", max_length=400, blank=True, null=True)