How to apply unique constraints using annotation

@Column(name = "userId")
    @UniqueConstraint
    private Integer userId;

I am using these annotation for entering data into database table. i want to make use开发者_开发技巧rId field unique field. but when i am doing like it it is showing me error @UniqueConstraints is disallowed for this location.

@Column(name = "userId",unique=true)

or if its an DB generated ID you can also do this

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Integer id;

Here's an example of how to use @UniqueConstraint:

@Entity
@Table(name = "contact", 
  uniqueConstraints = @UniqueConstraint(columnNames = {"name", "company_id"}))
public class Contact {
  ...
}

This specifies that the combination of the "name" column and the "company_id" column will be unique.

And this is the explanation of the Hibernate doc version 3.5 for @UniqueConstraint definition.

 @Entity
    @Table(name="tbl_sky",uniqueConstraints = {@UniqueConstraint(columnNames={"month", "day"})})
    public class Sky implements Serializable {
       ...
    }

and this is for Hibernate 4.3 example for @UniqueConstraint