[Answer]-Django ORM: wrapper for model objects

What you are talking about is perfectly doable with Django by using a custom model manager:

class MyModelManager(models.Manager):
    def get_query_set(self):
        return super(MyModelManager, self).get_query_set().annotate(size=Sum('id', field='order_size_weight*requested_selling_price'))


class MyModel(models.Model):
    objects = MyModelManager()

    # fields

Also see other similar topics:

• Is it possible to override .objects on a django model?
• Override djangos's object.all() with the request data
• Django custom model managers