@EmbeddedId with @GeneratedValue in @Embeddable

Question

I have a MySQL DB with the following structure (excerpt):

CREATE TABLE MENU(
    id_menu    TINYINT      UNSIGNED    NOT NULL    AUTO_INCREMENT,
    name             


        

Answer 1

Your JPA @Id does not need to match the database PK column(s). So long as it is unique then that is all that matters and as the associated column is an auto-increment column then this will be the case.

From https://en.wikibooks.org/wiki/Java_Persistence/Identity_and_Sequencing:

The JPA Id does not always have to match the database table primary key constraint, nor is a primary key or a unique constraint required.

So, while the PK for the associated table may be configured as PRIMARY KEY (id_operation, id_menu) it would seem, id_operation, through being auto-increment, could stand alone as a PK and therefore Operation can be mapped as below:

@Entity
public class Operation{

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @ManyToOne
    @JoinColumn(name = "id_menu")
    private Menu menu;
}

If you create the relevant IDClass then OperationRole can be mapped as below. For an example of this scenario and how the ID class would loook see:

https://en.wikibooks.org/wiki/Java_Persistence/Identity_and_Sequencing#Example_JPA_2.0_ManyToOne_id_annotation

@Entity
@IdClass(OperationRolePk.class)
public class OperationRole{

        @Id
        @ManyToOne
        @JoinColumn(name = "id_operation")
        private Operation operation;

        @Id
        @ManyToOne
        @JoinColumn(name = "id_menu")
        private Menu menu;

        @Id
        @ManyToOne
        @JoinColumn(name = "id_user")
        private User user;
}