Skip to content

Instantly share code, notes, and snippets.

What would you like to do?
Strict ForeignKeys
from __future__ import unicode_literals
from django.db import models
from django.db.models.fields.related_descriptors import ForwardManyToOneDescriptor # noqa
class RelationNotLoaded(Exception):
class StrictForwardManyToOne(ForwardManyToOneDescriptor):
def __get__(self, instance, cls=None):
return getattr(instance, self.cache_name)
except AttributeError:
raise RelationNotLoaded(
'Relation `{rel}` not loaded. Use `select_related` or '
def explicit_get(self, instance, cls=None):
return super(StrictForwardManyToOne, self).__get__(instance, cls)
class StrictForeignKey(models.ForeignKey):
def contribute_to_class(self, cls, name, **kwargs):
super(StrictForeignKey, self).contribute_to_class(cls, name, **kwargs)
# Override the descriptor defined by ForeignObject
descriptor = StrictForwardManyToOne(self)
setattr(cls,, descriptor)
# Add a method so you don't always have to use select_related
fetch_name = 'fetch_{rel}'.format(
setattr(cls, fetch_name, lambda inst: descriptor.explicit_get(inst))
# Create your models here.
class Author(models.Model):
name = models.TextField()
class Book(models.Model):
title = models.TextField()
author = StrictForeignKey(Author, on_delete=models.PROTECT, related_name='books')

This comment has been minimized.

Copy link

commented May 24, 2019

Nice work @kyle-eshares!

I'd like to use this snippet for a client of mine. Would it be possible for you to license it?

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
You can’t perform that action at this time.