How to recursively query in django efficiently?

Question

I have a model, which looks like:

class StaffMember(models.Model):

    id = models.OneToOneField(to=User, unique=True, primary_key=True, related_name=\'staf         


        

Answer 1

I found a solution to the problem. The recursive solution takes the node, goes to it's first child and goes deep down till bottom of the hierarchy. Then comes back up again to the second child (if exists), and then again goes down till the bottom. In short, it explores all the nodes one by one and appends all the members in an array. The solution I came up with, fetches the members layer-wise.

member = StaffMember.objects.get(id__id=user_id)

new_list = [member]

new_list = get_final_team(new_list)

def get_final_team(qs):
    team = []
    staffmembers = StaffMember.objects.filter(supervisor__in=qs)

    team += staffmembers 
    if staffmembers:
        interim_team_qs = get_final_team(staffmembers)
        for qs in interim_team_qs:
            team.append(qs)
    else:
        team = [qs]

    return team

The number of db calls this method entails is the number of layers (of hierarchy) that are present beneath the member whose team we want to find out.

Answer 2

If you're using a database that supports recursive common table expressions (e.g. PostgreSQL), this is precisely the use-case.

team = StaffMember.objects.raw('''
    WITH RECURSIVE team(id, supervisor) AS (
          SELECT id, supervisor 
          FROM staff_member
          WHERE id = 42
        UNION ALL
          SELECT sm.id, sm.supervisor
          FROM staff_member AS sm, team AS t
          WHERE sm.id = t.supervisor
        )
    SELECT * FROM team
''')

References: Raw SQL queries in Django
Recursive Common Table Expressions in PostgreSQL