Creating efficient database queries for hierarchical models (django)

Question

Consider this (django) model:

class Source(models.Model):
   # Some other fields
   type = models.ForeignKey(\'Type\')

class Type(models.Model):
    # Some othe         


        

Answer 1

django-mptt or django-treebeard are great helpers for hierarchical data. They both add extra metadata to your model to allow efficient queries.

if you choose to use django-treebeard your model could look something like this:

from django.db import models
from treebeard.mp_tree import MP_Node

class Source(models.Model):
    # Some other fields
    type = models.ForeignKey('Type')

class Type(MP_Node):
    # Some other fields
    name = models.CharField(max_length=100)

    # parent gets added automatically by treebeard
    # parent = models.ForeignKey('self', blank=True, null=True)

and could be queried like this:

# get all Sources of Type type and descendants of type
type = Type.objects.get(name='Radio')
Source.objects.filter(type__in=type.get_descendants())

see https://django-treebeard.readthedocs.io/en/latest/api.html for more possible queries