[Django] #24470: Serialization of base classes is not customizable for migrations

[Django]

#24470: Serialization of base classes is not customizable for migrations
-------------------------------+--------------------
     Reporter:  rockymeza      |      Owner:  nobody
         Type:  Uncategorized  |     Status:  new
    Component:  Migrations     |    Version:  1.7
     Severity:  Normal         |   Keywords:
 Triage Stage:  Unreviewed     |  Has patch:  0
Easy pickings:  0              |      UI/UX:  0
-------------------------------+--------------------
 I have a base class that is created by a class factory for one of my
 models. You can see an example [https://github.com/fusionbox/django-
 widgy/blob/master/widgy/models/mixins.py#L97-L117 here], but basically it
 works like this:

 {{{#!python
 def CreateBaseClass(arg):
     class cls(object):
         def get_arg(self):
             return arg

     return cls


 class MyModel(CreateBaseClass('foo'), models.Model):
     # ...
 }}}

 When I run makemigrations, it serializes the base classes to something
 like this:

 {{{#!python
         migrations.CreateModel(
             name='MyModel',
             fields=[
                 ('id', models.AutoField(verbose_name='ID',
 serialize=False, auto_created=True, primary_key=True)),
             ],
             options={},
             bases=(myapp.models.cls, models.Model),
         ),
 }}}

 But this errors because myapp.models.cls doesn't exist.

 I think that Django should allow the base classes to customize their
 serialization so that the migration would end up something like this:

 {{{#!python
             bases=(myapp.models.CreateBaseClass('foo'), models.Model),
 }}}

 This could be done through a classmethod called deconstruct_class, and it
 would be used like this:

 {{{#!python
 def CreateBaseClass(arg):
     class cls(object):
         @classmethod
         def deconstruct_class(cls):
             return 'myapp.models.CreateBaseClass', (arg,), {}

         # ...

     return cls
 }}}

 Here are some related tickets:
 #23950, #22951

 Thanks,

--
Ticket URL: <https://code.djangoproject.com/ticket/24470>
Django <https://code.djangoproject.com/>
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