Single custom Manager for Multiple models in Django

Question

I have several models connected to each other with ForeignKeys relationships.
The main one in this sort of hierarchy contains a owner field.

I would like to create a single custom manager for all these models that changes the returned queryset depending on the models that is calling it.

I know that manager can access self.model to get the model that it is attached to.

Class Main(models.Model)
  owner=models.ForeignKey (User)
  owned = OwnedManager()

Class Second(models.Model)
  main=models.ForeignKey('Main')
  owned = OwnedManager()

Class Third(models.Model)
  second=models.ForeignKey('Second')
  owned = OwnedManager()

I would like my Custom Manager to have this sort of behavior:

class OwnedManager(models.Manager): 
    def get_owned_objs(self, owner):
        if self.model == 'Main': # WRONG: How do I get the model name?
            owned_main = self.filter(owner=owner)
            return owned_main
        elif self.model == 'Second':
            owned_second = self.filter(main__owner=owner)
            return owned_second
        else:
            owned_third = self.filter(second__main__owner=owner)
            return owned_third

In order to have a consistent way to call it across different models, like so:

main_object.owned.get_owned_objs(owner=user1) # of the Model Main
second_object.owned.get_owned_objs(owner=user1) # of the Model Second
third_object.owned.get_owned_objs(owner=user1) # of the Model Third

QUESTION:

• self.model == 'Main' is wrong. I don't get the model name like this. Is there a way to get it?
• Is this efficient? Do you know a better way to implement this? Maybe Custom Managers Inheritance?

EDIT - MY SOLUTION: The accepted answer below is a good solution but I also found a way to get the model name of the particular model calling the custom manager, that is:

if self.model.__name__ == 'Main':

The key here is the attribute __name__

Answer 1

1) Make abstract model

class AbstractModel(models.Model):
    class Meta(models.Meta):
        abstract = True

    objects = OwnedManager()

2) Inherit your models from AbstractModel, put some key in meta

class Model(AbstractModel)
    class Meta(AbstractModel.Meta):
        filter_key = 'some_key'

3) Redesign your OwnedManager

class OwnedManager(models.Manager): 
    def get_owned_objs(self, owner):
        if hasattr(self.model._meta, 'filter_key'):
            return self.filter(**{self.model._meta.filter_key: owner})

Now you can use SomeModel.objects.get_owned_objs(owner=user1) in any inherited models, where filter_key is setted without getting models's name.