mybatis关系映射之一对多和多对一

一. 简介:

本实例使用顾客和订单的例子做说明: 一个顾客可以有多个订单, 一个订单只对应一个顾客

二. 例子:

1. 代码结构图:

2. 建表语句:

CREATE DATABASE test;    
  
USE test;  
  
CREATE TABLE person(  
  personId VARCHAR(36) PRIMARY KEY,  
  personName VARCHAR(64),  
  personAddress VARCHAR(128),  
  personTel VARCHAR(11)  
);  
  
CREATE TABLE orders(  
  orderId VARCHAR(36) PRIMARY KEY,  
  orderNumber VARCHAR(20),  
  orderPrice INT,  
  pid VARCHAR(36)  
);  
  
INSERT INTO person VALUES('001', 'Jack', 'Wuhan', '1234567');  
INSERT INTO orders VALUES('O_00001', '00001', 100, '001');  
INSERT INTO orders VALUES('O_00002', '00002', 200, '001');  
  
SELECT p.*, o.*  
FROM person p   
  JOIN orders o ON (p.personId=o.pid)  
WHERE p.personId = '001'  

3. 顾客实体:

/** 
 * 客户实体  
 */  
public class Person {  
  
    private String id;  
    private String name;  
    private String address;  
    private String tel;  
      
    private List<Order> orders;  
      
    @Override  
    public String toString() {  
        return "{id: " + id + ", name: " + name + ", address: " + address + ", tel: " + tel + "}";  
    }  
}  

4. 订单实体:

/** 
 * 订单实体 
 */  
public class Order {  
  
    private String id;  
    private String number;  
    private int price;  
      
    private Person person;   
      
    @Override  
    public String toString() {  
        return "{id: " + id + ", number: " + number + ", price: " + price + "}";  
    }  
  
}  

5. 一对多实体配置: Person.xml

<?xml version="1.0" encoding="UTF-8" ?>  
<!DOCTYPE mapper  
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"  
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">  
<mapper namespace="com.zdp.domain.Person">  
  
    <resultMap type="Person" id="personBean">  
        <id column="personId" property="id"/>  
        <result column="personName" property="name"/>  
        <result column="personAddress" property="address"/>  
        <result column="personTel" property="tel"/>  
          
        <!-- 一对多的关系 -->  
        <!-- property: 指的是集合属性的值, ofType：指的是集合中元素的类型 -->  
        <collection property="orders" ofType="Order">  
            <id column="orderId" property="id"/>  
            <result column="orderNumber" property="number"/>  
            <result column="orderPrice" property="price"/>  
        </collection>  
    </resultMap>  
      
    <!-- 根据id查询Person, 关联将Orders查询出来 -->  
    <select id="selectPersonById" parameterType="string" resultMap="personBean">  
        select p.*, o.* from person p, orders o where p.personId  = o.pid and p.personId = #{id}  
    </select>  
      
</mapper>  

6. 多对一实体配置:

<?xml version="1.0" encoding="UTF-8" ?>  
<!DOCTYPE mapper  
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"  
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">  
<mapper namespace="com.zdp.domain.Order">  
    <resultMap type="Order" id="orderBean">  
        <id column="orderId" property="id"/>  
        <result column="orderNumber" property="number"/>  
        <result column="orderPrice" property="price"/>  
          
        <!-- 多对一的关系 -->  
        <!-- property: 指的是属性的值, javaType：指的是属性的类型-->  
        <association property="person" javaType="Person">  
            <id column="personId" property="id"/>  
            <result column="personName" property="name"/>  
            <result column="personAddress" property="address"/>  
            <result column="personTel" property="tel"/>  
        </association>  
    </resultMap>  
      
    <!-- 根据id查询Order, 关联将Person查询出来 -->  
    <select id="selectOrderById" parameterType="string" resultMap="orderBean">  
        select p.*, o.* from person p, orders o where p.personId  = o.pid and o.orderId = #{id}  
    </select>  
      
</mapper>  

7. 总配置: sqlMapConfig.xml

<?xml version="1.0" encoding="UTF-8" ?>  
<!DOCTYPE configuration  
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"  
"http://mybatis.org/dtd/mybatis-3-config.dtd">  
<configuration>  
    <typeAliases>  
        <typeAlias type="com.zdp.domain.Person" alias="Person"/>    
        <typeAlias type="com.zdp.domain.Order" alias="Order"/>    
    </typeAliases>  
    <environments default="development">  
        <environment id="development">  
            <transactionManager type="JDBC" />  
            <dataSource type="POOLED">  
                <property name="driver" value="com.mysql.jdbc.Driver" />  
                <property name="url" value="jdbc:mysql://localhost/test" />  
                <property name="username" value="root" />  
                <property name="password" value="root" />  
            </dataSource>  
        </environment>  
    </environments>  
    <mappers>  
        <!-- 映射文件的位置 -->  
        <mapper resource="com/zdp/domain/Person.xml" />  
        <mapper resource="com/zdp/domain/Order.xml" />  
    </mappers>  
</configuration>  

8. 测试文件:

/** 
 * 测试一对多和多对一 
 */  
public class MybatisTest {  
  
    private SqlSessionFactory ssf;   
  
    @Before  
    public void initSF() throws Exception {  
        String resource = "sqlMapConfig.xml";  
        InputStream inputStream = Resources.getResourceAsStream(resource);  
        ssf = new SqlSessionFactoryBuilder().build(inputStream);  
    }  
  
    @Test//一对多关联查询  
    public void selectPersonById()throws Exception{  
        SqlSession session = ssf.openSession();  
        Person person = session.selectOne("com.zdp.domain.Person.selectPersonById", "001");  
        System.out.println(person.getOrders());  
    }  
      
    @Test//多对一关联查询  
    public void selectOrderById()throws Exception{  
        SqlSession session = ssf.openSession();  
        Order order = session.selectOne("com.zdp.domain.Order.selectOrderById", "O_00001");  
        System.out.println(order.getPerson().getName());  
    }  
}