[Django]-Django Cannot set values on a ManyToManyField which specifies an intermediary model. Use Manager instead

If you are allowed to modify class Membership, adding auto_created = True might solve your problem,

class Membership(models.Model): 
    class Meta:
        auto_created = True

In Django 1.7, the error message is changed to “Cannot set values on a ManyToManyField which specifies an intermediary model”. The solution is the same.

NOTE: This will remove your intermediate model entirely, and all the additional fields with it.

I had a similar error message on a different problem. I post it here just in case it helps others.

I’ve added a new ManyToManyField on an existing model. This model was used in a ModelForm built with an exclude field.

I fixed the problem by add the new field in the excluded ones.

As of the Django 2.2 release you can also specify a through_defaults on the field in order to use add, create and assignment:

The RelatedManager.add(), create(), remove(), set(), get_or_create(),
and update_or_create() methods are now allowed on many-to-many
relationships with intermediate models. The new through_defaults
argument is used to specify values for new intermediate model
instance(s).

In your case since all the fields already have defaults it might just work in 2.2.

As specified in https://docs.djangoproject.com/en/2.1/topics/db/models/

"Unlike normal many-to-many fields, you can’t use add(), create(), or set() to create relationships"

This means for django version 2.1 ,these methods are impossible. But the same page of django 2.2 documentation https://docs.djangoproject.com/en/2.2/topics/db/models/ tells that:

"You can also use add(), create(), or set() to create relationships, as long as you specify through_defaults for any required fields"

So just update the django to 2.2 or newer versions to use the above methods and while creating objects give the argument ‘through_defaults’ as a python dictionary with keys as your extra field names and values as their default values.