Which annotation need to use for unique constraint in JPA entity, unique=true or @UniqueConstraints at class level with single unique column

Question

I have some existing project and used both unique =true at column level and @UniqueConstraints at entity class level for the same column as below. I am currently doing code refactor so need suggestion to improve the code.

@Table(name = "sales_order", uniqueConstraints = @UniqueConstraint(columnNames = "order_no"))
public class SalesOrder implements java.io.Serializable {

    private static final long                 serialVersionUID = 6008509031685325038L;

    //primary key column with some other columns 
    
    @Column(name = "order_no", unique = true, nullable = false)
    private String orderNo;
}

We can not use both for the same unique column right ? In the above code, which one is the best to use or define unique constraint? I would say if it's single column unique then can use unique=true at column level and if unique key contains multiple columns then use @UniqueConstraints.

Answer 1

"Best" is obviously subjective, but your proposed approach works well. And it describes the only limitation, forcing the use of one over the other.

I would say if it's single column unique then can use unique=true at column level and if unique key contains multiple columns then use @UniqueConstraints.

Of course, one might argue for always using @UniqueConstraints in order to make the code more uniform. But that is really a matter of code style.