JPA ManyToMany Join Table具有PK的所有屬性

Question

我正在使用Hibernate 3.3.1並且正在建模這個示例表結構 ，但是我在創建具有額外屬性的連接表時遇到了麻煩。

它是Order和Product表之間的多對多關系。 連接表是Order Detail表。 我按照這里提到的方法。

現在我有了實體

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

和

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

和

@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;
}

和

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

我使用Apache Derby進行測試，但是我遇到了生成的表結構的問題。

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);

它似乎已創建我的所有列作為主鍵。 為什么會這樣？

Answer 1

您使用實體的類作為IdClass的參數。 這是不正確的。 應使用Id類。 另外，不需要在連接實體中用於id的單獨字段。

去尋找下面的代碼。 我不能保證它可以在如此舊的Hibernate版本中運行，但絕對可以肯定。 無論如何都值得嘗試。 如果你想使用JPA 2.0功能，更新到至少3.5.X版本（或者更確切地說是更新版本）也不會有什么壞處。 為了節省空間，剝離了構造者/平等等。

@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;
}

更新15/08/2017在JPA 2.1及更高版本中，您不需要為復合ID添加類，您可以這樣做：

@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

下面的代碼似乎根據需要生成表，我在MySQL上測試過它（只是表創建，而不是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詳細信息如下

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)