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

After playing around with this a bit, I found that the solutions were all too slow, because mptt itself is scanning the cache multiple times to get_children.

Capitalizing on the fact that mptt returns rows in the correct order to easily build trees, I made this:

def flat_tree_to_dict(nodes, max_depth):
    tree = []
    last_levels = [None] * max_depth
    for n in nodes:
        d = {'name': n.name}
        if n.level == 0:
            tree.append(d)
        else:
            parent_dict = last_levels[n.level - 1]
            if 'children' not in parent_dict:
                parent_dict['children'] = []
            parent_dict['children'].append(d)
        last_levels[n.level] = d
    return tree

For my data set, this runs 10x faster than other solutions because it's O(n), only iterating the data once.

I use it like this:

json.dumps(flat_tree_to_dict(Model.objects.all(), 4), indent=4)