How would I grab only articles with comments that

Question

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

class Article
  include Mongoid::Document

  has_many :comments
end

class Comment
  include Mongoid::Document

  belongs_to :article
end

Answer 1

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

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

Answer 2

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