How to prevent self (recursive) selection for FK / MTM fields in the Django Admin

Question

Given a model with ForeignKeyField (FKF) or ManyToManyField (MTMF) fields with a foreignkey to \'self\' how can I prevent self (recursive) selection within the Djan

Answer 1

You can also override the get_form method of the ModelAdmin like so:

def get_form(self, request, obj=None, **kwargs):
    """
    Modify the fields in the form that are self-referential by
    removing self instance from queryset
    """
    form = super().get_form(request, obj=None, **kwargs)
    # obj won't exist yet for create page
    if obj:
        # Finds fieldnames of related fields whose model is self
        rmself_fields = [f.name for f in self.model._meta.get_fields() if (
            f.concrete and f.is_relation and f.related_model is self.model)]
        for fieldname in rmself_fields:
            form.base_fields[fieldname]._queryset =
                form.base_fields[fieldname]._queryset.exclude(id=obj.id)
    return form

Note that this is a on-size-fits-all solution that automatically finds self-referencing model fields and removes self from all of them :-)