django-polymorphic Filter by child type

问题

I have models structure like below:

class MyObject(PolymorphicModel):
    group = models.ForeignKey(Group)

class Group(PolymorphicModel):
    pass

class SpecialGroup(Group):
    pass

Now, I would like to select all MyObjects, which group is of type SpecialGroup.

Is it possible to achieve it with QuerySet API, without running raw SQL? The only working solution I came up with was by running additional 'select' SQL query using .extra().

Thanks in advance, Cheers!

回答1:

Internally, django_polymorphic uses Django's ContentType framework to determine the actual class used for each model.

from django.contrib.contenttypes.models import ContentType

MyObject.objects.filter(group__polymorphic_ctype=ContentType.objects.get_for_model(SpecialGroup))

来源：https://stackoverflow.com/questions/22675596/django-polymorphic-filter-by-child-type