How can I restrict ForeignKey choices using a reverse relationship in Django admin?

Hello there,

I have a basic model structure where the Parent model includes a ForeignKey field named default_child that uses limit_choices_to to filter choices based on a reverse relationship from the Child model. Here's the code:

PYTHONCopied
class Parent(models.Model):
    name = models.CharField(...
    default_child = models.ForeignKey(
        to="Child",
        null=True,
        on_delete=models.SET_NULL,
        limit_choices_to=models.Q(parent_id=models.F("id")),
        related_name="+",
    )

class Child(models.Model):
    name = models.CharField(...
    parent = models.ForeignKey(
        to="Parent",
        related_name="children",
    )

I was expecting the default_child field in the admin panel’s change page to be populated with suitable choices, but it remains empty. Is there an alternative method to achieve this filtering?