title: How to enforce unique field value in java Google App Engine
body: <p>I am try to find out how to enforce uniqueness in fields other than the unique id.</p>
  
  <p>Example:</p>
  
  <pre><code>@PersistenceCapable(identityType = IdentityType.APPLICATION)
  public class User implements IsSerializable {
      @PrimaryKey
      @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
      private Long id;
  
      @Persistent
      private String name; 
  
      @Persistent
      private String email; // &lt;= I want this to be unique as well
  }
  </code></pre>
  
  <p>In the example above, how can I enforce uniqueness of the email value across the database?</p>
  
  <p>Daniel</p>