Allow add/create on m2m intermediate tables if all the non-FK fields have defaults or are NULLable

[Gergely Kontra]

Add/create is currently disabled on m2m relations that use an intermediate table. This is due to the fact that values to populate the intermediate table cannot be provided using the add/create calls.

However, what if the intermediate model has reasonable default values, so
one can assign model A to B without extra info?

In my case, I just want to syncronize 2 databases, and I would like to
mark relationships, that are already synced. So, in my case, the
intermediate table contains a boolean, which defaults to false, and
will become true, when the data is synced.

In this case adding relations without explicitly creating the intermediate table would be great.

(based on ​this thread in the ML)

[Alex Gaynor]

Marking as accepted because it makes sense.

[Russell Keith-Magee]

Updated description and summary to describe the problem better.

[Ales Zoulek]

I did just a quick workaround. It's far from complete and universal code, but it works for me and could help some of you. :)

from django.db.models.fields.related import ReverseManyRelatedObjectsDescriptor as DjangoReverseManyRelatedObjectsDescriptor
from django.db import models



class ReverseManyRelatedObjectsDescriptor(DjangoReverseManyRelatedObjectsDescriptor):
    """Partialy supports add method in ManyToManyField with 'through'"""
    def __get__(self, *args, **kwargs):
        manager = super(ReverseManyRelatedObjectsDescriptor, self).__get__(*args, **kwargs)
        def add(*objs):
            manager._add_items(manager.source_col_name, manager.target_col_name, *objs)
        add.alters_data = True
        manager.add = add
        return manager


class ManyToManyField(models.ManyToManyField):

    def contribute_to_class(self, cls, name):
        ret = super(ManyToManyField, self).contribute_to_class(cls, name)
        setattr(cls, self.name, ReverseManyRelatedObjectsDescriptor(self))
        return ret

# Continue with your models here. Use ManyToManyField class where needed.
class A(models.Model)
    b = ManyToManyField(B, through=AB)

...

[(none)]

Milestone post-1.0 deleted

[Johannes Dollinger]

Duplicate of #9475.