Django - model mixin doesn't work as expected

Question

In PipedriveSync model I use GenericForeignKey so any model can have PipedriveSync object related.

class PipedriveSync(TimeStampedModel):
    ...
    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
    object_id = models.PositiveIntegerField()
    content_object = GenericForeignKey('content_type', 'object_id')

And I use GenericRelation to be able to reference backwards this object. For example user.pipedrivesyncs.all()

Take a look at User

class User(AbstractUser):
    pipedrivesyncs = GenericRelation('pipedrive.PipedriveSync')

Since I have to specify the same pipedrivesyncs for many models, I decided to create a mixin for that (there are couple of methods there too but it doesn't matter now).

class PipedriveSyncRelatedMixin():
    pipedrivesyncs = GenericRelation('pipedrive.PipedriveSync')

And I use it this way

class User(PipedriveSyncRelatedMixin,AbstractUser):
    pass

The problem is that this Mixin doesn't work the way it works when I specify pipedrivesyncs manually.

Case of specifying pipedrivesyncs manually:

> u = User.objects.first()
> u.pipedrivesyncs.first()
> <PipedriveSync: PipedriveSync object (20)>

Case when using Mixin

> u = User.objects.first()
> u.pipedrivesyncs.first()
> AttributeError: 'GenericRelation' object has no attribute 'first'

Where is the difference and can I use Mixin for this purpose?

Answer 1

Your mixin has to be abstract and heritance should come from models.Model i think.

class PipedriveSyncRelatedMixin(models.Model):
    pipedrivesyncs = GenericRelation('pipedrive.PipedriveSync')

    class Meta:
        abstract = True