title: How to do multiple column UniqueConstraint in hbm?
body: <p>Working on some legacy hibernate code.</p>
  
  <p>How do I do the following with hbm.xml(hibernate mapping file) instead of with annotations?</p>
  
  <pre><code>@Table(name="users", uniqueConstraints = {
      @UniqueConstraint(columnNames={"username", "client"}),
      @UniqueConstraint(columnNames={"email", "client"})
  })
  public class User implements Serializable {
      private static final long serialVersionUID = 1L;
      @Id
      private int id;
      private String username;
      private String email;
      private Client client;
  }
  </code></pre>