Aggregate with Mongoid

Question

MongoDB has a new Aggregation Framework and I'm trying to figure out how to use it with Mongoid. It appears there is a branch of Moped with this functionality as discussed here. I've updated to MongoDB 2.2 and tried installing this branch of Moped on my app like this:

gem 'moped', git: 'git://github.com/mongoid/moped.git', branch: 'aggregation-support'

but aggregation is still not working. This is the call I am using to test it:

= Post.all.aggregate({ "$group" => { "_id" => "$_id" } })

UPDATE

In the mongo shell this works:

db.users.aggregate({ $group : { _id : "$_id" }})

so I'm thinking it's a Mongoid issue...any word on this would be great!

Is it because on the shell you are accessing the users collection and in Mongoid the posts collection? ^^ — Christoph Geschwind
Have you tried Post.collection.aggregate("$group" => { "_id" => "$_id" }) ? — Christoph Geschwind
@neon did you get the aggregate framework to work with moped and mongoid using that branch and would you like to update your question with the solution. — brg
It seems like you're missing the aggregation function in your update? Are you trying to sum, find a min or a max or what? In any case, in Mongoid 3.0.x the aggregation methods "avg", "max", "min", and "sum" are documented here: mongoid.org/en/mongoid/docs/querying.html#aggregations — GSP

yacc yacc · Accepted Answer · 2013-03-21T18:16:45

Since 3.0.1, Mongoid requires MongoDB 2.2 and supports the new aggregation framework.

You can now call aggregate on collections:

project = {"$project" => 
  {
    "charges" => 1,
    "year"    => { "$year" => "$created"}, "month" => { "$month" => "$created"},
    "week"    => { "$week" => "$created"}, "day"   => { "$dayOfYear" => "$created"} 
  }
}
group =  { "$group" =>
  { "_id" => {"year"=>"$year", "week"=>"$week"}, "count" => { "$sum" => 1 } } 
}
Charge.collection.aggregate([project,group])

Aggregate with Mongoid

2 Answers