'GenericForeignKey' object has no attribute 'deconstruct'

[corebreaker]

The class django.contrib.contenttypes.generic.GenericForeignKey is a field type for models, used for my example by application cmsplugin_rt.rt_carousel, application that i modified in order to use it in Django 1.7 .

But class django.contrib.contenttypes.generic.GenericForeignKey has not the required method deconstruct.

I posted this ticket cause class django.contrib.contenttypes.generic.GenericForeignKey could be used by others as field in models and the exception could be raised for this reason.

The lack is just that class django.contrib.contenttypes.generic.GenericForeignKey has not implemented the required method deconstruct. This method should be added if not, we have to subclass GenericForeignKey at every time we use it as field in models. It's just a big work to do each time.

[Baptiste Mispelon]

Hi,

How do you get that error message?
From what I've tried, using a GenericForeignKey in a model works with migrations and doesn't trigger any particular error.

Thanks.

[corebreaker]

Django 1.7 project simple example that shows the bug.

[corebreaker]

I joined a Django project that has the bug. Use migrate command to see it. The result is:

Operations to perform:
  Synchronize unmigrated apps: staticfiles, messages
  Apply all migrations: admin, contenttypes, formbug, auth, sessions
Synchronizing apps without migrations:
  Creating tables...
  Installing custom SQL...
  Installing indexes...
Running migrations:
  Applying contenttypes.0001_initial... OK
  Applying auth.0001_initial... OK
  Applying admin.0001_initial... OK
  Applying formbug.0001_initial...Traceback (most recent call last):
  File "./manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/__init__.py", line 385, in execute_from_command_line
    utility.execute()
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/__init__.py", line 377, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/base.py", line 288, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/base.py", line 338, in execute
    output = self.handle(*args, **options)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/commands/migrate.py", line 160, in handle
    executor.migrate(targets, plan, fake=options.get("fake", False))
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/executor.py", line 63, in migrate
    self.apply_migration(migration, fake=fake)
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/executor.py", line 91, in apply_migration
    if self.detect_soft_applied(migration):
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/executor.py", line 135, in detect_soft_applied
    apps = project_state.render()
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/state.py", line 67, in render
    model.render(self.apps)
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/state.py", line 305, in render
    body = dict(self.construct_fields())
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/state.py", line 276, in construct_fields
    _, path, args, kwargs = field.deconstruct()

I just used GenericForeignKey class as a model field. In Django 1.7, model fields require to implement deconstruct method. But GenericForeignKey has not implemented this method.

[Tim Graham]

Did you generate the migration file using makemigrations? It seems to be missing most of the models from the sample project. I get an entirely different one if I delete the file you provided and then run makemigrations (GenericForeignKey doesn't appear in the resulting migration). I'll attach it for reference.