mybatis关系映射之一对多和多对一

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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());
    }
}