How would I grab only articles with comments that were created 20 minutes ago?

Question

Using mongodb and mongoid. How would one grab all articles. Only articles with comments created 20 minutes ago?

class Article
  include Mongoid::Document

           


        

Answer 1

articles = Article.where(:_id.in => Comment.where(:created_at => 20.minutes.ago).map(&:article_id))

Answer 2

you can also do this, which should be more efficient:

articles = Article.where(:"comments.created_at".gt => 20.minutes.ago)