SQL JPA - Multiple columns as primary key

Question

If i want severeal Column to make up an ID.

SQL example :

CONSTRAINT [PK_NAME] PRIMARY KEY ([Column1],[Column2],[Column3])

How can

Answer 1

Use @Embeddable and @EmbeddedId.

Example:

@Entity
public class Project {
    @EmbeddedId ProjectId id;
     :
}

@Embeddable
Class ProjectId {
    int departmentId;
    long projectId;
}

More information here http://www.objectdb.com/java/jpa/entity/id#Embedded_Primary_Key_