What is the correct way to do a HAVING in a MongoDB GROUP BY?

Question

For what would be this query in SQL (to find duplicates):

SELECT userId, name FROM col GROUP BY userId, name HAVING COUNT(*)>1

I perform

Answer 1

New answer using Mongo aggregation framework

After this question was asked and answered, 10gen released Mongodb version 2.2 with an aggregation framework. The new best way to do this query is:

db.col.aggregate( [
   { $group: { _id: { userId: "$userId", name: "$name" },
               count: { $sum: 1 } } },
   { $match: { count: { $gt: 1 } } },
   { $project: { _id: 0, 
                 userId: "$_id.userId", 
                 name: "$_id.name", 
                 count: 1}}
] )

10gen has a handy SQL to Mongo Aggregation conversion chart worth bookmarking.