Type with models inheritance

gistfile1.py

##### Test ...
#
# DocumentService(name='document1').save()
# VideoService(name='video1').save()
# DocumentService(name='document2').save()
# VideoService(name='video2').save()
#
# DocumentService.objects.all()
#> [<DocumentService: <class 'test_app.models.DocumentService'>: document1>, <DocumentService: <class 'test_app.models.DocumentService'>: document2>]
#
# VideoService.objects.all()
#> [<VideoService: <class 'test_app.models.VideoService'>: video1>, <VideoService: <class 'test_app.models.VideoService'>: video2>]
#
# Service.objects.all()
#> [<DocumentService: <class 'test_app.models.DocumentService'>: document1>, <VideoService: <class 'test_app.models.VideoService'>: video1>, <DocumentService: <class 'test_app.models.DocumentService'>: document2>, <VideoService: <class 'test_app.models.VideoService'>: video2>]

from django.db import models
from django.contrib.contenttypes.models import ContentType
from test_app.manager import TypeFilter

class ServiceMetaclass(models.base.ModelBase):
    def __call__(cls, *args, **kwargs):
        obj = super(ServiceMetaclass, cls).__call__(*args, **kwargs)
        return obj.get_object(cls)


class Service(models.Model):

    __metaclass__ = ServiceMetaclass

    name = models.CharField(max_length=25)
    age = models.CharField(max_length=25)
    #todo: choices with querys ContentTypes for admin work
    content_type = models.ForeignKey(ContentType)
    objects = models.Manager()
    objects_typed = TypeFilter()

    def __unicode__(self):
        return '{cls}: {name}'.format(cls=self.__class__, name=self.name)

    def save(self, *args, **kwargs):
        self.content_type = ContentType.objects.get_for_model(self)
        super(Service, self).save(*args, **kwargs)

    def get_object(self, unr_class):
        #object not saved, let it continue
        if self.id is None:
            return self
        #try instance Service when isn't (Service.objets.all())
        if self.__class__ != self.content_type.model_class():
            return self.content_type.model_class().objects.get(pk=self.pk)
        #try instance Service childs (DocumentService.objects.all())
        else:
            return self

class DocumentService(Service):
    def hi(self):
        print 'i am document service'

class VideoService(Service):

    def hi(self):
        print 'i am video service'