hibernate开发中遇到多对多的问题,可以转换为两个一对多

例如，现在有商品表，订单表，两者是多对多的关系，

--订单表
create table ORDERS
(
ID            NUMBER(8) not null,
TOTAL         NUMBER(8,2) not null,
CREATED_DATE VARCHAR2(40) not null,
REALNAME      VARCHAR2(20),
TELPHONE      VARCHAR2(20),
MOBILE        NUMBER(20),
ADDRESS       VARCHAR2(200) not null,
POSTCODE      VARCHAR2(12),
STATE         NUMBER(1),
ACCOUNT_ID    VARCHAR2(40),
PAYMENT_ID    NUMBER(4),
DELIVERY_ID   NUMBER(4),
PAYMENT_STATE NUMBER(1),
MEMO          VARCHAR2(400)
)

--商品表

create table PRODUCT
(
ID           NUMBER(8) not null,
NAME         VARCHAR2(200) not null,
CREATED_DATE VARCHAR2(40),
DESCRIPTION VARCHAR2(4000),
IMAGEURL     VARCHAR2(200),
PRICE        NUMBER(6,2) not null,
STOCK        NUMBER(8),
STATE        NUMBER(1) not null,
CATEGORY_ID NUMBER(4) not null,
DISCOUNT     NUMBER(2)
)

--中间表

create table ORDERITEM
(
ORDER_ID     NUMBER(8),
PRODUCT_ID   NUMBER(8),
ORIGIN_PRICE NUMBER(6,2),
PRICE        NUMBER(6,2),
QUANTITY     NUMBER(6),
ID           VARCHAR2(40) not null
)

传统的多对多映射会在order.hbm.xml中这样设置：

      <set name="products" table="orderitem">
        <key column="order_id"></key>
        <many-to-many class="com.shop.model.Product">
           <column name="product_id"></column>
        </many-to-many>
        </set>

但是，此时中间表orderitem中多了三个字段,此时就不能用上面这种方法了，

那么就可以转化成两个一对多（或者说两个多对一）

步骤：

1.生成orderitem的POJO类，并改造成如下内容：

public class Orderitem implements java.io.Serializable {

// Fields

private String id;
private Double originPrice;
private Double price;
private Long quantity;

private Order order;
private Product product;

// Constructors

/** default constructor */
public Orderitem() {
}

// Property accessors

public String getId() {
   return this.id;
}

public void setId(String id) {
   this.id = id;
}

public Double getOriginPrice() {
   return this.originPrice;
}

public void setOriginPrice(Double originPrice) {
   this.originPrice = originPrice;
}

public Double getPrice() {
   return this.price;
}

public void setPrice(Double price) {
   this.price = price;
}

public Long getQuantity() {
   return this.quantity;
}

public void setQuantity(Long quantity) {
   this.quantity = quantity;
}

public Order getOrder() {
   return order;
}

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

public Product getProduct() {
   return product;
}

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

}

2.配置映射文件

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- 
    Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
    <class name="com.shop.model.Orderitem" table="ORDERITEM" schema="STORE">
        <id name="id" type="java.lang.String">
            <column name="ID" length="10" />
            <generator class="uuid.hex"></generator>
        </id>
        <property name="originPrice" type="java.lang.Double">
            <column name="ORIGIN_PRICE" precision="6" />
        </property>
        <property name="price" type="java.lang.Double">
            <column name="PRICE" precision="6" />
        </property>
        <property name="quantity" type="java.lang.Long">
            <column name="QUANTITY" precision="6" scale="0" />
        </property>
       

       <many-to-one name="order" class="com.shop.model.Order"
        cascade="save-update" >
        <column name="order_Id"></column>
        </many-to-one>
        <many-to-one name="product" class="com.shop.model.Product">
          <column name="product_Id"></column>
        </many-to-one>
    </class>
</hibernate-mapping>

3.接下来就变成多对一事务操作了（当然，从另一个方向看，就是一对多了）。