Recursive QuerySet with django

Question

I have this model referencing itself to allow building a tree:

class PartCategory(models.Model):
    parent = models.ForeignKey('PartCategory', on_delete=models.DO_NOTHING, null=True, default=None, blank=True)
    name = models.TextField()

I now have an SQL query to get one element and all of its child in one select (in this example the element with id=64):

WITH RECURSIVE
  under_partcategory(id,name, parent_id,level) AS (
    select api_partcategory.id,api_partcategory.name,api_partcategory.parent_id,0 from api_partcategory where api_partcategory.id=64
    UNION ALL
    SELECT api_partcategory.id,api_partcategory.name,api_partcategory.parent_id, under_partcategory.level+1
    FROM api_partcategory JOIN under_partcategory ON api_partcategory.parent_id=under_partcategory.id
    ORDER BY 2
  )
SELECT * FROM under_partcategory;

I am searching a way to express this query inside a QuerySet to allow adding filtering options and fields construction from my model but I don't quite know if it's kind of possible.

Can I construct a composite QuerySet made from some kind of raw query built from my model, and at the same time allowing to use the filter and order_by capabilities?

Edit:

To be more specific I would like to have a QuerySet I can use this whay:

PartCategory.recursive.filter(64)

Internally it would build the request by replacing all embraced parts with elements from PartCategory model:

WITH RECURSIVE
  under_{model name}({model fields},level) AS (
    select {model fields},0 from {model name} {where {model name}.id=64 #extracted from filter}
    UNION ALL
    SELECT {model fields}, under_{model_name}.level+1
    FROM {model name} JOIN under_{model_name} ON {model_name}.parent_id=under_{model_name}.id
    ORDER BY 2
  )
SELECT * FROM under_{model_name};

I'm playing with a custom managers to try to build this but for now I don't know how to build {model fields} from my model and how to return an object eligible for filter.

Edit 2:

As stated by colwin I made it with django-mptt but not exactly as I was thinking in first place.

My model with django-mptt becomes:

from mptt.models import MPTTModel, TreeForeignKey

class PartCategory(MPTTModel):
    parent = TreeForeignKey('self', null=True, blank=True, related_name='children', db_index=True)
    name = models.TextField()
    class MPTTMeta:
        order_insertion_by = ['name']

And to extract my item 64 with all its childrens I now do:

categories = PartCategory.objects.get(id=64).get_descendants(include_self=True)

This is quite straightforward !

Answer 1

Shouldn't this work for you?

parts = PartCategory.objects.raw('''
    WITH RECURSIVE
    under_partcategory(id,name, parent_id,level) AS (
    select   api_partcategory.id,api_partcategory.name,api_partcategory.parent_id,0 from api_partcategory where api_partcategory.id=64
    UNION ALL
    SELECT api_partcategory.id,api_partcategory.name,api_partcategory.parent_id, under_partcategory.level+1
    FROM api_partcategory JOIN under_partcategory ON api_partcategory.parent_id=under_partcategory.id
    ORDER BY 2
  )
SELECT * FROM under_partcategory;
''')

You can also look at https://github.com/django-mptt/django-mptt

Answer 2

I had the same problem, and wanted to avoid raw SQL. While I'm on PostgreSQL, this is for a package that may be used under other DB contexts. I found this:

https://django-mptt.readthedocs.io/en/latest/overview.html