title: NSPredicate problem with column name
body: <p>I am trying to query a table using NSPredicate. Here is essentially what I'm doing:</p>
  
  <pre><code>NSNumber *value = [NSNumber numberWithInteger: 2];
  NSString *columnName = @"something_id";
  
  NSLog(@"%@ == %@", columnName, value);
  NSPredicate *refQuery = [NSPredicate predicateWithFormat: @"%@ == %@", columnName, value];
  </code></pre>
  
  <p>NSLog prints out what I expect ("something_id == 2"), but the predicate doesn't work.
  However, the predicate DOES work if I change it to: </p>
  
  <pre><code>NSPredicate *refQuery = [NSPredicate predicateWithFormat: @"something_id == %@", value];
  </code></pre>
  
  <p>So why won't this work and how can I fix it?</p>