复合主键，使用@IdClass - 列“id”不能是 null

Question

I have an entity with a composite primary key.

id - version will be the primary key.

id	version	column A
1	1	some data
1	2	some data
2	1	some data
2	2	some data

I am using @IdClass for handling the composite primary key.

@Entity
@IdClass(MyKey.class)
public class YourEntity {
   @Id
   private int id;
   @Id
   private int version;
}


public class MyKey implements Serializable {
   private int id;
   private int version;
}

When I want to insert new row to the table, in other words I want to add new id , it complains that Column 'id' cannot be null .

I don't want id be null . According to my table, when I insert new row, it should add new id with value 3 .

Answer 1

If I understand you correctly, you want to use AUTO_INCREMENT for id column. You should be able to use @GeneratedValue(strategy = GenerationType.IDENTITY) for id field of your entity. But, unfortunately, you can not do it due to HHH-9662 . And this is not critical bug as it is not violate jpa specification.

As workaround, you can use an approach that was described in Vlad Mihalcea's article .

Assuming that you have the following table:

create table test_my_entity (
    id int not null AUTO_INCREMENT,
    version int,
    name  varchar(50),

    primary key (id, version)
);

You can use the following mapping:

import org.hibernate.annotations.SQLInsert;
import javax.persistence.EmbeddedId;
// ...

@Entity
@Table(name = "test_my_entity")
@SQLInsert(sql = "insert into test_my_entity(name, id, version) values (?, ?, ?)")
public class MyEntity {

    @EmbeddedId
    private MyEntityPk pk;

    @Column(name = "name")
    private String name;

    // getters and setters ...
}


@Embeddable
public class MyEntityPk implements Serializable {
    private int id;
    private int version;

    public MyEntityPk() {
    }

    public MyEntityPk(int version) {
        this.version = version;
    }

    public MyEntityPk(int id, int version) {
        this.id = id;
        this.version = version;
    }

    public int getId() {
        return id;
    }

    public int getVersion() {
        return version;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        MyEntityPk that = (MyEntityPk) o;
        return version == that.version && id == that.id;
    }

    @Override
    public int hashCode() {
        return Objects.hash(id, version);
    }

}

and example how you can insert new row:

MyEntity myEntity = new MyEntity();
myEntity.setPk(new MyEntityPk(5));
myEntity.setName("Yulia");
entityManager.persist(myEntity);