title: Define unique key in hibernate
body: <p>I have three models in my project.</p>
  
  <pre><code> public class Bank{
     private int id;
     private String title;
     ....
  }
  public class Branch{
     private Bank bank;
     private int id;
     private String title;
     ....
  }
  public class Account{
     private Branch branch;
     private int id;
     private String accountNumber;
     private String title;
     ....
  }
  </code></pre>
  
  <p>how to define the accountNumber and id Of bank combined as a unique key?</p>