Expanding the list of relationship field arguments - django

Question

I’m looking for a way to expand the list of relationship field arguments, e.g. to add a predicate for each direction of the relation. My first guess was to define a subclass of models.ForeignKey
class NewForeignKey(models.ForeignKey):
def __init__(self, parent, pred='', reverse_pred='', **kwargs):
self.pred = pred,
self.reverse_pred = reverse_pred
super(NewForeignKey, self).__init__(parent, **kwargs)
Then use this subclass in my models as in the following example:
class Question(models.Model):
question_text = models.CharField(max_length=200)
pub_date = models.DateTimeField('date published')
class Choice(models.Model):
question = NewForeignKey (Question,
pred="refers to",
reverse_pred="includes",
on_delete=models.CASCADE)
choice_text = models.CharField(max_length=200)
votes = models.IntegerField(default=0)
Initially, this seemed to work fine, however, when I tried to pass it through makemigrations it failed with the following error message:
Traceback (most recent call last):
File "manage.py", line 10, in <module>
execute_from_command_line(sys.argv)
File "C:\Python27\lib\site-packages\django\core\management\__init__.py", line 354, in execute_from_command_line
utility.execute()
File "C:\Python27\lib\site-packages\django\core\management\__init__.py", line 346, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "C:\Python27\lib\site-packages\django\core\management\base.py", line 394, in run_from_argv
self.execute(*args, **cmd_options)
File "C:\Python27\lib\site-packages\django\core\management\base.py", line 445, in execute
output = self.handle(*args, **options)
File "C:\Python27\lib\site-packages\django\core\management\commands\makemigrations.py", line 99, in handle
ProjectState.from_apps(apps),
File "C:\Python27\lib\site-packages\django\db\migrations\state.py", line 178, in from_apps
model_state = ModelState.from_model(model)
File "C:\Python27\lib\site-packages\django\db\migrations\state.py", line 354, in from_model
e,
TypeError: Couldn't reconstruct field question on polls.Choice: __init__() takes at least 2 arguments (1 given)
To make things even simpler I tried from scratch to migrate as follows:
first without the FK,
then added the FK as models.ForeignKey and
finally replaced models.ForeignKey with NewForeignKey
Migrations after step (1) and (2) were successful (obviously). makemigrations after step (3) fails all the time with the same result whether I skip step (2) or not.
Digging deeper, I couldn’t find an explanation why this shouldn’t be possible. I understand that Django models have to be subclassed from django.db.models.Model (see here), but this isn’t the case with models.ForeignKey.
A clarification on this issue and/or any suggestions for a workaround or a clever alternative that would allow the use of additional relationship field arguments would be appreciated.