title: NSPredicate to Search Collection
body: <p>I have a tableview with a search bar.  I was able to use NSPredicate to search the tableview when I add the items to another array:</p>
  
  <pre><code>for(head in items){
     [desc addObject:head.DESC];
     [category addObject:head.CATEGORY];
   }
  
  - (void)filterContentForSearchText:(NSString*)searchText scope:(NSString*)scope
  {
     NSPredicate *resultPredicate = [NSPredicate predicateWithFormat:@"self CONTAINS[cd] %@", searchText];
  searchResults = [desc filteredArrayUsingPredicate:resultPredicate];
  }
  </code></pre>
  
  <p>Now I want to keep the collection together so that a tableView didSelectRowAtIndexPath will be able to use the category object.</p>
  
  <p>I load my table view like this:</p>
  
  <pre><code>for (int i = 0; i &lt; [items count]; i++){
      head = [items objectAtIndex:indexPath.row];
      labelName.text = head.DESC;
  </code></pre>
  
  <p>How can I get my NSPredicate to search the collection for head.DESC?</p>
  
  <pre><code> #pragma mark Search Results
  - (void)filterContentForSearchText:(NSString*)searchText scope:(NSString*)scope
    {
  NSPredicate *resultPredicate = [NSPredicate predicateWithFormat:@"self CONTAINS[cd] %@", searchText];
  searchResults = [items filteredArrayUsingPredicate:resultPredicate];
  }
  </code></pre>
  
  <p>Currently, I am getting this exception when running the above code.</p>
  
  <pre><code>reason: 'Can't use in/contains operator with collection &lt;Order: 0x7b22e900&gt; (not a collection)'
  </code></pre>