fastest way to create JSON to reflect a tree structure in Python / Django using mptt

Question

What\'s the fastest way in Python (Django) to create a JSON based upon a Django queryset. Note that parsing it in the template as proposed here is not an option.

The ba

Answer 1

I suspect by far the biggest slowdown is that this will do 1 database query per node. The json rendering is trivial in comparison to the hundreds of round-trips to your database.

You should cache the children on each node so that those queries can be done all at once. django-mptt has a cache_tree_children() function you can do this with.

import json
from mptt.templatetags.mptt_tags import cache_tree_children

def recursive_node_to_dict(node):
    result = {
        'id': node.pk,
        'name': node.name,
    }
    children = [recursive_node_to_dict(c) for c in node.get_children()]
    if children:
        result['children'] = children
    return result

root_nodes = cache_tree_children(Node.objects.all())
dicts = []
for n in root_nodes:
    dicts.append(recursive_node_to_dict(n))

print json.dumps(dicts, indent=4)

Custom json encoding, while it might provide a slight speedup in some scenarios, is something I'd highly discourage, as it will be a lot of code, and it's something that's easy to get very wrong.