Mybatis学习笔记9 - 鉴别器discriminator

鉴别器：mybatis可以使用discriminator判断某列的值，然后根据某列的值改变封装行为。

示例如下：

DeptmentMapper接口定义：
package com.mybatis.dao;

import com.mybatis.bean.Department;

public interface DeptmentMapper {
    public Department getDeptById(Integer id);
}

DeptmentMapper.xml文件定义：
<?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.mybatis.dao.DeptmentMapper">
    <!--public Department getDeptById(Integer id);-->
    <select id="getDeptById" resultType="com.mybatis.bean.Department">
        select id,dept_name departmentName from tbl_dept where id=#{id}
    </select>
</mapper>

EmployeeMapper接口定义：
package com.mybatis.dao;

import com.mybatis.bean.Employee;

public interface EmployeeMapper {
    public Employee getEmpByIdWithDept(Integer id);
}

EmployeeMapper.xml文件定义：
<?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.mybatis.dao.EmployeeMapper">
    <!-- <discriminator javaType=""></discriminator>
		鉴别器：mybatis可以使用discriminator判断某列的值，然后根据某列的值改变封装行为
		封装Employee：
			如果查出的是女生：就把部门信息查询出来，否则不查询；
			如果是男生，把last_name这一列的值赋值给email;
	 -->
    <resultMap type="com.mybatis.bean.Employee" id="MyEmpDis">
        <id column="id" property="id"/>
        <result column="last_name" property="lastName"/>
        <result column="email" property="email"/>
        <result column="gender" property="gender"/>
        <!--
            column：指定判定的列名
            javaType：列值对应的java类型  -->
        <discriminator javaType="java.lang.Integer" column="gender">
            <!--女生  resultType:指定封装的结果类型；不能缺少。/resultMap-->
            <case value="0" resultType="com.mybatis.bean.Employee">
                <association property="dept"
                             select="com.mybatis.dao.DeptmentMapper.getDeptById"
                             column="d_id">
                </association>
            </case>
            <!--男生 ;如果是男生，把last_name这一列的值赋值给email; -->
            <case value="1" resultType="com.mybatis.bean.Employee">
                <id column="id" property="id"/>
                <result column="last_name" property="lastName"/>
                <result column="last_name" property="email"/>
                <result column="gender" property="gender"/>
            </case>
        </discriminator>
    </resultMap>

    <select id="getEmpByIdWithDept" resultMap="MyEmpDis">
       select * from tbl_employee where id=#{id}
    </select>
</mapper>

测试代码：
package com.mybatis.demo;

import com.mybatis.bean.Department;
import com.mybatis.bean.Employee;
import com.mybatis.dao.DeptmentMapper;
import com.mybatis.dao.EmployeeMapper;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;

public class MyTest {
    public SqlSessionFactory getSqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        return new SqlSessionFactoryBuilder().build(inputStream);
    }

    @Test
    public void testResultMap() throws IOException {
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        SqlSession openSession = sqlSessionFactory.openSession(true);
        try {
            EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
            Employee girl = mapper.getEmpByIdWithDept(1);
            System.out.println(girl.getDept());
            Employee boy = mapper.getEmpByIdWithDept(7);
            System.out.println(boy.getDept());
        } finally {
            openSession.close();
        }
    }
}