System check fields.E300 does not allow for related fields involving auto_created through models.

[Jason Bruce]

The model system checks will raise the fields.E300 error if you make an auto_created through model the target of a related field. Here is an example of models that will trigger this error:

class E300TestModelA(models.Model):
    pass

class E300TestModelB(models.Model):
    many_to_many_rel = models.ManyToManyField(E300TestModelA)

class E300TestModelC(models.Model):
    one_to_one_rel = models.OneToOneField("check_framework.E300TestModelB_many_to_many_rel", on_delete=models.CASCADE)

I realize this might be an unusual thing to do, however I have a use case that requires this and thought I would create this ticket in case others agree that this should be changed. I will create a pull request shortly.

[Jason Bruce]

I created a pull request with a fix for the bug and a regression test.

[Sarah Boyce]

Thank you for the report and patch

[Jason Bruce]

I updated my pr. Please let me know if there is anything else I can improve.