Question

Ive got a painting model. votes is embedded into painting. How can i query all paintings and order by the number of votes? IN theory, I would like to list down all paintings starting with the ones with the most votes.

For reference purposes. Here is the definition of the two models:

class Painting
  include Mongoid::Document
  include Mongoid::Timestamps

  field :title, :type => String

  embeds_many :votes
  ...
end

class Vote
  include Mongoid::Document
  include Mongoid::Timestamps

  embedded_in :painting, :inverse_of => :votes
  ...
end

Answer 1

You can do it by using counter cache column. Once you implement this functionality like mentioned here: http://railscasts.com/episodes/23-counter-cache-column, paintings table will contain votes_count column which holds the number of votes for each painting

Then you can easily add named_scope in your painting.rb model to order paintings by number of votes:

class Painting
  named_scope :order_by_maximum_votes, :order => "votes_count DESC"
end

Then you can fetch all paintings like this way:

@paintings = Painting.all.order_by_maximum_votes