How to correctly use auto_created attribute in django?

问题

I need to create my own intermediate model.

class class1(models.Model)

class class2(models.Model):
    field1 = models.ManyToManyField(class1, through="class3")

class class3(models.Model):
    field1 = models.ForeignKey(class1)
    field2 = models.ForeignKey(class2)
    field3 = models.IntegerField()

    class Meta:
        auto_created = True

I use "auto_created=True" because in the following code, I had the error :

AttributeError: Cannot use add() on a ManyToManyField which specifies an intermediary model.

for m2m_field in self._meta.many_to_many:
    for m2m_link in getattr(self, m2m_field.get_attname()).all():
        getattr(to_object, m2m_field.get_attname()).add(m2m_link)

Now it works fine, but when I try to do a makemigration, django wants to remove my class3 (the intermediate class), and removing the "through" attribute in the field1 in class2.

What am I doing wrong ? Any solutions ?

Tks all.

回答1:

As far as I am aware, the auto_created attribute in the Meta class is undocumented, so you should avoid using it.

As the AttributeError says, it is not possible to use add() for a many to many field that uses an intermediary model. The correct fix is to create an instance of the intermediate model, instead of using add().

class3.objects.create(field_1=c1, field_2=c2, field_3=1).

See the docs on extra fields in many to many relationships for more info.

来源：https://stackoverflow.com/questions/34394323/how-to-correctly-use-auto-created-attribute-in-django