sfendell sfendell -3 years ago 115
Python Question

Making a tree structure in django models?

I want to have a model with 2 fields, children and parent. How do I do this in django? I have something like this

from django.db import models
class FooModel(models.Model)
parent = models.ForeignKey('self', blank=True, null=True)
children = models.ManyToOneRel('self', blank=True, null=True)

def __init__(self, *args, **kwargs):
super(FooModel, self).__init__(*args, **kwargs)
self.parent.children.add(self)


But I don't think i'm supposed to use the ManyToOneRel like this (especially because it's giving me a keyword error on 'blank'). Any advice?

Answer Source

ManyToOneRel is an internal implementation class, it's not for use in your models.

But why do you think you need it anyway? As the documentation explains in detail, when you define a ForeignKey, you automatically get a reverse relation. So in your case, if you define parent then you automatically get self.foomodel_set already: and you can make it even more explicit by using the related_name parameter:

parent = models.ForeignKey('self', blank=True, null=True, related_name='children')

Note that if you're planning on doing complicated things with trees, you probably want to be using the django-mptt library.

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