如何从嵌套的activerecord集合中获取所有记录

Question

I have an ActiveRecord query that i need help with.

Lets say we have a user and he has multiple libraries. In each library, there are many collections. In each collection, he has many books.

How do I get a list of all his books?

I know I can do libraries.each |library| library.collections.each do |collections| collection.books.each do |book| books << book.title

but I'm hoping for a simpler methodology then this.

Answer 1

You can use rails' has_many through for it

class User
  has_many :libraries
  has_many :collections, through: :libraries
  has_many :books, -> { uniq }, through: :collections
end

Then you can simply query

@user = User.first
@user_books = @user.books