title: How to introduce multi-column constraint with JPA annotations?
body: <p>I am trying to introduce a multi-key constraint on a JPA-mapped entity:</p>
  
  <pre><code>public class InventoryItem {
      @Id
      private Long id;
  
      @Version 
      private Long version;
  
      @ManyToOne
      @JoinColumn("productId")
      private Product product;
  
      @Column(nullable=false);
      private long serial;
  }
  </code></pre>
  
  <p>Basically (product, serial) pair should be unique, but I only found a way to say that serial should be unique.  This obviously isn't a good idea since different products might have same serial numbers.  </p>
  
  <p>Is there a way to generate this constraint via JPA or am I forced to manually create it to DB?</p>