5

I'm using Django-MPTT to do a display a simple 2 level hierarchy (root => child(ren)). I'm looking for a way to structure my queryset so that nodes get returned with the root node having the most children first and the node with the least children (if any) last.

NFicano
  • 1,065
  • 1
  • 11
  • 26

2 Answers2

4

Take a look at your parent field and make note of the related_name. Suppose it is children. Then do the following:

from django.db.models import Count

MyMPTTModel.objects.root_nodes().annotate(
    Count('children')).order_by('-children__count')

If you need access to the child instances themselves, you may also want to look at doing a qs.prefetch_related('children') as well.

DylanYoung
  • 2,423
  • 27
  • 30
  • It's also worth noting that if your hierarchy is indeed only two levels deep, you probably don't get any benefit from mptt as a simple parent field and order field should suffice and be more performant... though I could be wrong. – DylanYoung Aug 08 '17 at 18:13
3

something like this should do it:

from mptt.templatetags.mptt_tags import cache_tree_children
qs = qs.filter(level__lt=2)
root_nodes = cache_tree_children(qs)
root_nodes.sort(key=lambda node: len(node.get_children()), reverse=True)
craigds
  • 2,072
  • 14
  • 25