title: Can multiple (two) persistent stores be used with one object model, while maintaining relations from one to the other?
body: <p><strong>Introduction</strong></p>
  
  <p>My iOS project ships with a Core Data persistent store weighing some 160MB in SQLite format. There is a ton of grouped information in there, in which users should be able to mark favorites. For this, I need (at least part of) the database to have write capabilities. But of course persistent stores that ship in the application bundle are by design read-only. </p>
  
  <p>If you want the store to have read-write capabilities, you should copy it to, e.g. the app's documents folder. I don't want to do this, because then the app would be twice the size, while the main part of that database is read-only anyway. That would be a waste of resources.</p>
  
  <p><strong>Multiple persistent stores for NSPersistentStoreCoordinator</strong></p>
  
  <p>This is why I thought of using two persistent stores. The first would be the big one in the bundle, and the second could be a small one in the documents folder, storing special "favorite" entities with relationships to the big store.</p>
  
  <p>I know something is possible in this regard, but I can't find the specifics. Should one only use multiple stores if you also have multiple object models? Can one object model be 'distributed' over two persistent stores? When browsing through the <a href="http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CoreData/Articles/cdUsingPersistentStores.html">Core Data Programming docs</a>, I can't find any real reference about how to set this up. Also Marcus Zarra's book doesn't seem to delve into this topic:</p>
  
  <blockquote>
    <p>It is possible to add more than one NSPersistentStore to the NSPersistentStoreCoordinator, which can be useful when dealing with data that is split into multiple files. However, in our exam- ple, we have a single file. (<a href="http://books.google.com/books?id=tFOXOwAACAAJ&amp;dq=inauthor%3a%22Marcus+S.+Zarra%22&amp;hl=nl&amp;ei=Mg92TaedMY_qOeus2bsG&amp;sa=X&amp;oi=book_result&amp;ct=result&amp;resnum=1&amp;ved=0CDMQ6AEwAA">Marcus Zarra: "Core Data - Apple's API for Persisting Data on Mac OS X" page 71</a>) </p>
  </blockquote>
  
  <p><strong>The Question</strong></p>
  
  <p>Who could tell me if what I'm thinking of is possible with Core Data and multiple persistent stores? And could you maybe provide a hint about how to achieve this? Online/offline resources that deal with the topic are very much appreciated too.</p>