title: CoreData many to many relationship insert and delete operations
body: <p>I have a question about CoreData relationships.</p>
  
  <p>I have this situation:</p>
  
  <p>I have DOG and BONE entity.</p>
  
  <ul>
  <li>Each DOG can have more BONE.</li>
  <li>Each BONE can have more DOG.</li>
  </ul>
  
  <p>So I need a many to many relationship.</p>
  
  <p>how do I set the report delete in CoreData? what kind?</p>
  
  <p>I think I need something as this:</p>
  
  <ul>
  <li>When I delete a BONE I do not have to remove the DOG;</li>
  <li>When I delete a DOG I do not have to remove the BONE if this is used from a DOG.</li>
  <li>When I delete a DOG I have to remove the BONEs if these are used only from this DOG.</li>
  </ul>
  
  <p>Is this mechanism automatic for CoreData if I impose this relationship type?</p>
  
  <p>About insert?</p>
  
  <p>For example: I need to insert a DOG with some Bones: How do I check if the bone already exists? 
  Every bone in my table has an ID</p>