mongoose recursive schema

navigation.js

schema.statics.findRecursive = function(cb) {
    this.find({ show: true, menu: true })
        .select('order parent url title')
        .sort({ parent: -1, order: 1 })
        .lean()
        .exec(function(err, items) {
            if (err) cb(err);

            var o = {},
                arr = [];
            items.forEach(function(item) {
                item.sub = [];
                o[item._id] = item;
            });
            for (var i in o) {
                var item = o[i];
                if (item.parent) {
                    o[item.parent].sub.push(item);
                    delete o[i];
                }
            }
            for (var i in o) {
                arr.push(o[i]);
            }
            cb(null, arr);
        });
};