N+1 problem in mongoid

Question

I'm using Mongoid to work with MongoDB in Rails.

What I'm looking for is something like active record include. Currently I failed to find such method in mongoid orm.

Anybody know how to solve this problem in mongoid or perhaps in mongomapper, which is known as another good alternative.

Answer 1

Now that some time has passed, Mongoid has indeed added support for this. See the "Eager Loading" section here:
http://docs.mongodb.org/ecosystem/tutorial/ruby-mongoid-tutorial/#eager-loading

Band.includes(:albums).each do |band|
  p band.albums.first.name # Does not hit the database again.
end

I'd like to point out:

1. Rails' :include does not do a join
2. SQL and Mongo both need eager loading.
3. The N+1 problem happens in this type of scenario (query generated inside of loop):

.

<% @posts.each do |post| %>
  <% post.comments.each do |comment| %>
    <%= comment.title %>
  <% end %>
<% end %>

Looks like the link that @amrnt posted was merged into Mongoid.