Django self-recursive ManyToManyField filter query

Question

Hi, I have a model like so:

class Activity(models.Model):  
    title = models.CharField(max_length=200)
    summary = models.TextField(null=True, blank=True)  
    tasks = models.ManyToManyField('self', symmetrical=False, null=True, blank=True)  

It works like this, an activity can be linked to itself and the parent activity is called an 'Activity' and the child activity/activities will be called 'Task/Tasks'

How do I filter the model to get all the 'Activities' and How do I filter the model to get all the 'Tasks' ?

Thanks for all the help.

Answer 1

Here you go:

from django.db.models import Count

annotated_qs = Activity.objects.annotate(num_tasks=Count(tasks))

activities = annotated_qs.objects.filter(num_tasks=0)
tasks = annotated_qs.objects.filter(num_tasks__gt=0)

:)

You could do it with better performance without annotation, if you use __is_null=True, but I can't recall or quick google it's syntax right now.