Fixed #20777 -- Admin proxy model deletion regression

            if source_attr:

                self.add_edge(getattr(obj, source_attr), obj)

            else:

                if obj._meta.proxy:

                    # Take concrete model's instance to avoid mismatch in edges

                    obj = obj._meta.concrete_model(pk=obj.pk)

                self.add_edge(None, obj)

        try:

            return super(NestedObjects, self).collect(objs, source_attr=source_attr, **kwargs)

.. method:: Model.__eq__()

The equality method is defined such that instances with the same primary

key value and the same concrete class are considered equal. The term

concrete class means proxy model's first non-proxy parent or the class

itself if it isn't a proxy class.

key value and the same concrete class are considered equal. For proxy

models, concrete class is defined as the model's first non-proxy parent;

for all other models it is simply the model's class.

For example::

from django.contrib import admin

from .models import TrackerUser, ProxyTrackerUser

admin.site.register(TrackerUser)

admin.site.register(ProxyTrackerUser)

[

    {

        "pk": 100,

        "model": "auth.user",

        "fields": {

            "username": "super",

            "first_name": "Super",

            "last_name": "User",

            "is_active": true,

            "is_superuser": true,

            "is_staff": true,

            "last_login": "2007-05-30 13:20:10",

            "groups": [],

            "user_permissions": [],

            "password": "sha1$995a3$6011485ea3834267d719b4c801409b8b1ddd0158",

            "email": "super@example.com",

            "date_joined": "2007-05-30 13:20:10"

        }

    },

    {

        "pk": 100,

        "model": "proxy_models.BaseUser",

# Proxy models still works with filters (on related fields)

# and select_related, even when mixed with model inheritance

@python_2_unicode_compatible

class BaseUser(models.Model):

    name = models.CharField(max_length=255)

    def __str__(self):

        return ':'.join((self.__class__.__name__, self.name,))

class TrackerUser(BaseUser):

    status = models.CharField(max_length=50)