JPA ManyToMany Join Table has all attributes as PK

Question

I'm using Hibernate 3.3.1 and am following along in modelling this sample table structure, but I'm having trouble creating a join table with extra attributes.

It's the many-to-many relationship between the Order and Product table. The join table is the Order Detail table. I followed the approach mentioned here.

Now I have the entities

@Entity
@Table(name = "Orders")
public class Order {
    @OneToMany(mappedBy="order")
    private List<OrderDetail> orderItems;
}

and

@Entity
@Table(name="PRODUCTS")
public class Product {
    @OneToMany(mappedBy="product")
    private List<OrderDetail> orderItems;
}

and

@Entity
@IdClass(OrderDetail.class)
@Table(name = "ORDER_DETAIL")
public class OrderDetail implements Serializable {
    @Id
    @Column(name="ORDER_ID")
    private Long orderId;
    @Id
    @Column(name="PRODUCT_ID")
    private Long productId;

    @Column(name = "PRICE")
    private double price;

    @Column(name = "LAST_UPDATED_TIME")
    private Date lastUpdatedTime;

    @ManyToOne
    @JoinColumn(name = "ORDER_ID")
    private Order order;

    @ManyToOne
    @JoinColumn(name = "PRODUCT_ID")
    private Product product;
}

and

public class OrderDetailId implements Serializable {
    private Long orderId;
    private Long productId;
}

I used Apache Derby to do the test, but I'm having trouble with the generated table structure.

CREATE TABLE ORDER_DETAIL (
        PRODUCT_ID BIGINT NOT NULL,
        ORDER_ID BIGINT NOT NULL,
        LAST_UPDATED_TIME TIMESTAMP NOT NULL,
        PRICE DOUBLE NOT NULL
    );

CREATE INDEX SQL120323142938020 ON ORDER_DETAIL (PRODUCT_ID ASC);

CREATE UNIQUE INDEX SQL120323142937810 ON ORDER_DETAIL (PRODUCT_ID ASC, ORDER_ID ASC, LAST_UPDATED_TIME ASC, PRICE ASC);

ALTER TABLE ORDER_DETAIL ADD CONSTRAINT SQL120323142937810 PRIMARY KEY (PRODUCT_ID, ORDER_ID, LAST_UPDATED_TIME, PRICE);

ALTER TABLE ORDER_DETAIL ADD CONSTRAINT FK4A94AA82CC6D989A FOREIGN KEY (PRODUCT_ID)
    REFERENCES PRODUCTS (PROD_ID);

It seems that it has created all of my columns as the primary key. Why is this so?

Answer 1

You use class of your entity as an argument to IdClass. That is not correct. Class of Id should be used. Additionally separate fields for id in join entity are not needed.

Go for something like code below. I cannot guarantee that it works in such a old version of Hibernate, but works for sure in never ones. Worth of trying anyway. It would not hurt to update to at least 3.5.X version (or rather even fresher one) if you want to use JPA 2.0 features. Constructors/equals etc. are stripped away to save space.

@Entity
@Table(name = "Orders")
public class Order {
    @Id Long id;
    @OneToMany(mappedBy="order")
    private List<OrderDetail> orderItems;
}

@Entity
@Table(name="PRODUCTS")
public class Product {
    @Id Long id;
    @OneToMany(mappedBy="product")
    private List<OrderDetail> orderItems;
}

@Entity
@IdClass(OrderDetailId.class)
@Table(name = "ORDER_DETAIL")
public class OrderDetail implements Serializable {
    @Id @ManyToOne @JoinColumn(name = "ORDER_ID")
    private Order order;

    @Id @ManyToOne @JoinColumn(name = "PRODUCT_ID")
    private Product product;

    @Column(name = "PRICE") private double price;
    //Maybe you also want to use @TemporalType here
    @Column(name = "LAST_UPDATED_TIME") private Date lastUpdatedTime;
}

public class OrderDetailId implements Serializable {
    private Long order;
    private Long product;
}

UPDATE 15/08/2017 In JPA 2.1 and above you don't need to add a class for the composite Id and you can do it like this:

@Entity
@Table(name = "ORDER_DETAIL")
public class OrderDetail implements Serializable {
    @Id @ManyToOne @JoinColumn(name = "ORDER_ID")
    private Order order;

    @Id @ManyToOne @JoinColumn(name = "PRODUCT_ID")
    private Product product;

    @Column(name = "PRICE") private double price;
    //Maybe you also want to use @TemporalType here
    @Column(name = "LAST_UPDATED_TIME") private Date lastUpdatedTime;
}

Answer 2

The code below seems to generate tables as desired, I have tested it on MySQL (just the table creation, not CRUD):

@Entity
@Table(name = "orders")
public class Order {

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

    @OneToMany(mappedBy = "orderDetailId.order")
    private List<OrderDetail> orderItems;

    //get set …..

}

@Entity
@Table(name="products")
public class Product {

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

    @OneToMany(mappedBy = "orderDetailId.product")
    private List<OrderDetail> orderItems;   

    //get set ……
}

@Entity
@Table(name = "order_detail")
public class OrderDetail {

    @Id
    private OrderDetailId orderDetailId;

    private double price;

    @Temporal(TemporalType.TIMESTAMP)
    private Date lastUpdatedTime;

    //get set ….            
}

@Embeddable
public class OrderDetailId implements Serializable{

    private Order order;

    private Product product;

    @ManyToOne(fetch=FetchType.LAZY)
    @Access(AccessType.PROPERTY)
    public Order getOrder() {
        return order;
    }

    public void setOrder(Order order) {
        this.order = order;
    }

    @ManyToOne(fetch=FetchType.LAZY)
    @Access(AccessType.PROPERTY)
    public Product getProduct() {
        return product;
    }

    public void setProduct(Product product) {
        this.product = product;
    }

    //hash code equals override 
}

Hibernate DEBUG details as below

DEBUG: org.hibernate.tool.hbm2ddl.SchemaUpdate - create table order_detail (lastUpdatedTime datetime, price double precision not null, product_id bigint, order_id bigint, primary key (order_id, product_id)) ENGINE=InnoDB
DEBUG: org.hibernate.tool.hbm2ddl.SchemaUpdate - create table orders (id bigint not null auto_increment, primary key (id)) ENGINE=InnoDB
DEBUG: org.hibernate.tool.hbm2ddl.SchemaUpdate - create table products (id bigint not null auto_increment, primary key (id)) ENGINE=InnoDB
DEBUG: org.hibernate.tool.hbm2ddl.SchemaUpdate - alter table order_detail add index FK23AE5A622128CF91 (order_id), add constraint FK23AE5A622128CF91 foreign key (order_id) references orders (id)
DEBUG: org.hibernate.tool.hbm2ddl.SchemaUpdate - alter table order_detail add index FK23AE5A62EB201631 (product_id), add constraint FK23AE5A62EB201631 foreign key (product_id) references products (id)