title: Delete coredata objects with Custom migration
body: <p>I am trying to delete objects form coredata with coredata custom migration. I tried it inside following methods. It always failed with error.</p>
  <ul>
  <li><code>performCustomValidationForEntityMapping</code></li>
  <li><code>- (BOOL)endEntityMapping:(NSEntityMapping *)mapping manager:(NSMigrationManager *)manager error:(NSError **)error</code></li>
  <li><code>- (BOOL)beginEntityMapping:(NSEntityMapping *)mapping manager:(NSMigrationManager *)manager error:(NSError **)error</code></li>
  </ul>
  <p><strong>Error :</strong></p>
  <pre><code>Error Domain=NSCocoaErrorDomain Code=513 &quot;The file couldn’t be saved because you don’t have permission.&quot; UserInfo={NSPersistentStoreOptions={
    NSReadOnlyPersistentStoreOption = 1;
  }, reason=Unable to write to file opened Read Only.,
  </code></pre>