title: How to have repeated items in an Ordered To-Many relationship?
body: <p>In Core Data of Xcode 4.3.2, an Ordered To-Many relationship is modelled with <code>NSOrderedSet</code>. It works well until I found the need to have repeated items in the relationship; it should really be modelled in a <code>NSArray</code>.</p>
  
  <p>For example, in a music app, I have the following songs: <code>SongA, SongB, SongC</code> ,</p>
  
  <p>I may want a party play list where people insert songs in any order and could be repeated. The list may look something like: </p>
  
  <pre><code>[SongC, SongC, SongA, SongC]
  </code></pre>
  
  <p>The way Core Data currently works, the list would become:</p>
  
  <pre><code>[SongC, SongA]
  </code></pre>
  
  <p>I.e., all repeated items are dropped, as it is modelled with sets.</p>
  
  <p>So, coming back to my question: what is a good way to model repeated items in order in a relationship in Core Data?</p>