found record through association

Question

I have a modeling like this

class Room
  include Mongoid::Document
  field :name, type: String
  has_many :messages
end

class Message
  include Mongoid::Document
  field :content, type: String
  belongs_to :room
end

I need to found the top 3 rooms that had most messages in the last 24 hours, but I have no idea from where to start.
maybe something with map/reduce?

Answer 1

Try this using mongoid aggregation

Room.collection.aggregate(
  {
    "$match" => {"$messages.created_at" => {"$gte" => 1.day.ago}},
    "$group" => { 
      _id: '$messages', count: {"$sum" => 1}
    },
    { "$sort" => { count: -1 } }
  }
)