[Django]-Django: how do I query based on GenericForeignKey's fields?

by

73👍

✅

The Ticket.issue field you’ve defined will help you go from a Ticket instance to the Issue it’s attached to, but it won’t let you go backwards. You’re close with your second example, but you need to use the issue_id field – you can’t query on the GenericForeignKey (it just helps you retrieve the object when you have a Ticket instance). Try this:

from django.contrib.contenttypes.models import ContentType

issue = Issue.objects.get(scan=scan_obj)
tickets = Ticket.objects.filter(
    issue_id=issue.id,
    issue_ct=ContentType.objects.get_for_model(issue).id
    )
👤girasquid

15👍

Filtering across a GenericForeignKey can by creating a second model that shares the db_table with Ticket. First split up Ticket into an abstract model and concrete model.

class TicketBase(models.Model):
    issue_ct = models.ForeignKey(ContentType, related_name='issue_content_type')
    issue_id = models.PositiveIntegerField(null=True, blank=True)

    class Meta:
        abstract = True

class Ticket(TicketBase):
    issue = generic.GenericForeignKey('issue_ct', 'issue_id')

Then create a model that also subclasses TicketBase. This subclass will have all the same fields except issue which is instead defined as a ForeignKey. Adding a custom Manager allows it to be filtered to just a single ContentType.

Since this subclass does not need to be synced or migrated it can be created dynamically using type().

def subclass_for_content_type(content_type):
    class Meta:
        db_table = Ticket._meta.db_table

    class Manager(models.Manager):
        """ constrain queries to a single content type """
        def get_query_set(self):
            return super(Manager, self).get_query_set().filter(issue_ct=content_type)

    attrs = {
        'related_to': models.ForeignKey(content_type.model_class()),
        '__module__': 'myapp.models',
        'Meta': Meta,
        'objects': Manager()
    }
   return type("Ticket_%s" % content_type.name, (TicketBase,), attrs)
👤kreneskyp

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