Java JPA ManyToMany联接表的所有属性都是PK

我使用的是Hibernate 3.3.1，并且在建模方面也遵循这一点，但是我在创建带有额外属性的联接表时遇到了问题

这是

订单

和

产品

表之间的多对多关系。联接表是订单明细表。我采用了上述方法

现在我有了实体

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

及

我使用ApacheDerby进行测试，但生成的表结构有问题

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);

---

它似乎已经创建了我的所有列作为主键。为什么会这样？

您使用实体的类作为IdClass的参数。这是不对的。应使用Id的类。此外，联接实体中的id不需要单独的字段

选择下面的代码。我不能保证它在如此旧的Hibernate版本中工作，但可以肯定的是，它在从未有过的版本中工作。无论如何都值得一试。如果您想使用JPA2.0特性，至少更新到3.5.X版本（或者更高版本）不会有什么坏处。为了节省空间，构造函数/相等项等被剥离

@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;
}

---

下面的代码似乎可以根据需要生成表，我已经在MySQL上对其进行了测试（只是创建表，而不是CRUD）：

---

嗨，Mikko，啊，这只是一个想法，因为我仍然是JPA的初学者。我开始认为@ManyToMany注释似乎更像是一个细微差别，当你可以手动操作时？你不这么认为吗？我的理解有点肤浅，但这是我的印象。在所有情况下，我都能正确思考，知道，没有太多的地图是可能的。当关系的本质要求时，我强烈地倾向于总是使用多对多，因为它更干净，生成的代码更少。

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

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);

@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;
}

@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;
}

@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 
}

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)