Avoid N+1 queries when scopes are involved

scoped_n_plus_one.rb

class User < ActiveRecord::Base
  has_many :posts
  has_many :published_posts, -> { published }, class_name: "Post"
end

class Post < ActiveRecord::Base
  belongs_to :user
  scope :published, -> { where(status: :published) }
end

User.limit(10).preload(:published_posts).each do |user|
  user.published_posts.each do |post|
    puts post.title
  end
end