title: Is it possible to do a UNION like query with MagicalRecord/Core Data
body: <p>I have two Entities <code>Event</code> and <code>Action</code> which both inherit from <code>Message</code>. I've read that it's better for performance not to use single table inheritance. The events and actions are used in the app as an array of messages sorted by date. Currently I'm just selecting the events and actions separately then merging/sorting the new array. </p>
  
  <pre><code>    NSArray *events = [STEvent MR_findAll];
      NSArray *actions = [STAction MR_findAll];
      NSMutableArray *messages = [[NSMutableArray alloc] initWithArray:events];
      [messages addObjectsFromArray:actions];
      NSArray *messagesSorted;
      messagesSorted = [messages sortedArrayUsingComparator:^NSComparisonResult(id a, id b) {
          NSDate *first = [(STMessage*)a date];
          NSDate *second = [(STMessage*)b date];
          return [first compare:second];
      }];
  </code></pre>
  
  <p>Is it possible to do a SQL UNION like query with Magical Record or Core Data to retrieve everything at once?</p>