define some extra field methods so this rel acts more like a field which lets us use reversemanytoonedescriptor in both directions a foreignobject that uses startswith operator in its joins instead of the default equality operator this is logically a manytomany relation and creates a reversemanytoonedescriptor in both directions makes reversemanytoonedescriptor work in both directions this model is designed to yield no join conditions and raise an exception in join assql define some extra field methods so this rel acts more like a field which lets us use reversemanytoonedescriptor in both directions a foreignobject that uses startswith operator in its joins instead of the default equality operator this is logically a many to many relation and creates a reversemanytoonedescriptor in both directions makes reversemanytoonedescriptor work in both directions this model is designed to yield no join conditions and raise an exception in join as_sql
from django.db import models
from django.db.models.fields.related import ReverseManyToOneDescriptor
from django.db.models.lookups import StartsWith
from django.db.models.query_utils import PathInfo


class CustomForeignObjectRel(models.ForeignObjectRel):
    

    @property
    def foreign_related_fields(self):
        return tuple(lhs_field for lhs_field, rhs_field in self.field.related_fields)

    def get_attname(self):
        return self.name


class StartsWithRelation(models.ForeignObject):
    

    auto_created = False

    many_to_many = False
    many_to_one = True
    one_to_many = False
    one_to_one = False

    rel_class = CustomForeignObjectRel

    def __init__(self, *args, **kwargs):
        kwargs["on_delete"] = models.DO_NOTHING
        super().__init__(*args, **kwargs)

    @property
    def field(self):
        
        return self.remote_field

    def get_extra_restriction(self, alias, related_alias):
        to_field = self.remote_field.model._meta.get_field(self.to_fields[0])
        from_field = self.model._meta.get_field(self.from_fields[0])
        return StartsWith(to_field.get_col(alias), from_field.get_col(related_alias))

    def get_joining_fields(self, reverse_join=False):
        return ()

    def get_path_info(self, filtered_relation=None):
        to_opts = self.remote_field.model._meta
        from_opts = self.model._meta
        return [
            PathInfo(
                from_opts=from_opts,
                to_opts=to_opts,
                target_fields=(to_opts.pk,),
                join_field=self,
                m2m=False,
                direct=False,
                filtered_relation=filtered_relation,
            )
        ]

    def get_reverse_path_info(self, filtered_relation=None):
        to_opts = self.model._meta
        from_opts = self.remote_field.model._meta
        return [
            PathInfo(
                from_opts=from_opts,
                to_opts=to_opts,
                target_fields=(to_opts.pk,),
                join_field=self.remote_field,
                m2m=False,
                direct=False,
                filtered_relation=filtered_relation,
            )
        ]

    def contribute_to_class(self, cls, name, private_only=False):
        super().contribute_to_class(cls, name, private_only)
        setattr(cls, self.name, ReverseManyToOneDescriptor(self))


class BrokenContainsRelation(StartsWithRelation):
    

    def get_extra_restriction(self, alias, related_alias):
        return None


class SlugPage(models.Model):
    slug = models.CharField(max_length=20, unique=True)
    descendants = StartsWithRelation(
        "self",
        from_fields=["slug"],
        to_fields=["slug"],
        related_name="ascendants",
    )
    containers = BrokenContainsRelation(
        "self",
        from_fields=["slug"],
        to_fields=["slug"],
    )

    class Meta:
        ordering = ["slug"]

    def __str__(self):
        return "SlugPage %s" % self.slug