Question

so i’m using Mongoid and i want to return an object with it’s refference. lets say i have:

class User
  include Mongoid::Document
  has_many :pictures
end

class Picture
  include Mongoid::Document
  belongs_to :user
end

the problem is with this code:

users = User.all #goes to the db
users.each do |user|
  pic = user.pictures.first # <--- bad! hitting the db again here
end

so, how can return an object (user) that contains it’s refference so i wont need to hit the db again?

Answer 1

This would normally be done with joining in ActiveRecord. Something like this:

 User.includes(:pictures).each do |user|

But since MongoDB doesn’t support joins, there’s no way to load parent document and its referenced documents in one go. If this becomes a problem, you should consider embedding pictures in a user document (this, however, may cause more serious performance penalties).

Update

Mongoid has a way to eagerly load (search the page for “Eager Loading”) referenced relations, but still separate queries are made. Database won’t be hit on subsequent access of a relation.