MongoDB sorting documents by nested data

Question

Considering the following design for posts:

{
title: string,
body: string,
comments: [
    {name: string, comment: string, ...},
    {name: string, comment:          


        

Answer 1

You need to use the aggregate command

This should give you a list of post _id with the number of comments sorted by the count in reverse order.

You can use the $limit operators to return the x top rows. e.g. { $limit : 5 }

 db.posts.aggregate(
   { $unwind : "$comments" },
   { $group : { _id : "$_id" , number : { $sum : 1 } } },
   { $sort : { number : -1 } }
 );

Take a look http://docs.mongodb.org/manual/tutorial/aggregation-examples/