How to introduce multi-column constraint with JPA annotations?

Question

I am trying to introduce a multi-key constraint on a JPA-mapped entity:

public class InventoryItem {     @Id     private Long id;      @Version      private Long version;      @ManyToOne     @JoinColumn("productId")     private Product product;      @Column(nullable=false);     private long serial; } 

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.

Is there a way to generate this constraint via JPA or am I forced to manually create it to DB?

Answer 1

You can declare unique constraints using the @Table(uniqueConstraints = ...) annotation in your entity class, i.e.

@Entity @Table(uniqueConstraints={     @UniqueConstraint(columnNames = {"productId", "serial"}) })  public class InventoryItem {     ... } 

Note that this does not magically create the unique constraint in the database, you still need a DDL for it to be created. But seems like you are using some sort of automated tool for creating the database based on JPA entity definitions.