title: Check for duplicates when saving
body: <p>How to check for duplicates when saving new object?</p>
  
  <p>Scenario:</p>
  
  <ul>
  <li>check for duplicates by some query -> when no duplicates perform saving</li>
  </ul>
  
  <p>Is not good because between <strong><em>check</em></strong> and <strong><em>save</em></strong> there is plenty of time when other user can insert new object with the same data (high activity of users).</p>
  
  <p>Should I check for exception when saving or what?</p>