Hi.
According to documentation
<https://docs.djangoproject.com/en/1.9/topics/db/managers/#custom-managers-and-model-inheritance>
managers
defined on non-abstract base classes are not inherited by child classes. In
fact they're inherited via python MRO. I made pull request
<https://github.com/django/django/pull/5797> to fix it. I find this
inheritance embarrassing due to reasons, explained in documentation:
1. Managers defined on non-abstract base classes are *not* inherited by
child classes. If you want to reuse a manager from a non-abstract base,
redeclare it explicitly on the child class. These sorts of managers are
likely to be fairly specific to the class they are defined on, so
inheriting them can often lead to unexpected results (particularly as far
as the default manager goes). Therefore, they aren’t passed onto child
classes.
I also think this example shows some reasons why this inheritance is
embarrasing:
class SimpleComment(models.Model):
test_objects = models.Manager()
class BaseComment(models.Model):
pass
class Comment(BaseComment):
test_objects = models.Manager()
print(hasattr(models.SimpleComment, 'objects')) #False
print(hasattr(models.Comment, 'objects')) #True, we may expect False here,
since 'SimpleComment' gives False in similar sitation.
print(models.Comment.objects.model) #<class 'BaseComment'>, this manager is
not contributed to 'Comment' class
Tim Graham suggests asking if anyone relying on this inheritance and
documentation should be fixed instead. Any suggestions?
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