title: Trying to figure out what kind of relationships I should use
body: <p>Sinatra, Mongoid 3</p>
  
  <p>There 4 models: <code>User, Book, FavoriteBooks, ReadBooks, NewBooks</code>. Each user has their list of the favourites, read and new books. A book belongs to a list. But it's also possible to request an information about any book which means books should <strong>not</strong> be embedded into <code>FavoriteBooks, ReadBooks, NewBooks</code>.</p>
  
  <p>The part of the scheme:</p>
  
  <pre><code>class Book
   include Mongoid::Document
   belongs_to :favourite_books
   belongs_to :read_books
   belongs_to :new_books 
  end
  
  class FavoriteBook
   include Mongoid::Document
   has_many :books
  end
  
  #.... the same for ReadBooks and NewBooks
  
  
  class User
   include Mongoid::Document
   # what else?
  end
  </code></pre>
  
  <p>It seems like I missed something. </p>
  
  <p>What should I do to make a user "contain" the lists of <code>FavoriteBooks, ReadBooks, NewBooks</code>? Should I use one-to-one relationship?</p>