depth relation search

I am looking for a "pythonic" / "orm-ic" solution for this problem...

Model Soldier has a ManyToManyField to itself.

class Soldier(models.Model):
    ...
    subordinates = models.ManyToManyField('Soldier', ...)

A, B and C are Soldier objects

They form kind of "c开发者_如何学Gohain of command" like so: A > B > C

B is in A.subordinates.all()

C is in B.subordinates.all()

What's the best way to get all subordinates of A?

Something like A.get_all_subordinates(), that should return [B, C].

We don't know how many levels of this relation there is at runtime. (C can have some subordinates of his own, B can have siblings, etc.)

If you model the superior <-> subordinate relation with a many-to-many relation, you'll end up with a graph-like structure that can get arbitrary complex (e.g. circular relations). This will become very hard to query efficiently.

If you're after a tree-like structure (which means that every Soldier has at most one direct superior), you could use django-mptt:

from django.db import models
from mptt.models import MPTTModel

class Soldier(MPTTModel):
    parent = models.ForeignKey('self', null=True, blank=True)

Getting all the subordinates is then as easy as

subordinates = soldier.get_descendants()

And the best thing about get_descendants: it causes exactly one query to get all descendants.