使用discriminator实现鉴别器

Posted 2020-10-27 逆水乘舟，不进则退

1在人员接口实现方法

public Employee getEmpByIdStep(Integer id);

2在映射文件进行配置

<!-- public Employee getEmpByIdStep(Integer id);-->
<select id="getEmpByIdStep" resultMap="MyEmpDis">
select * from tbl_employee where id=#{id}
</select>

3写鉴别器

<!-- <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.atguigu.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="string" column="gender">
<!--女生 resultType:指定封装的结果类型；不能缺少。/resultMap-->
<case value="0" resultType="com.atguigu.mybatis.bean.Employee">
<association property="dept"
select="com.atguigu.mybatis.dao.DepartmentMapper.getDeptById"
column="did">
</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.atguigu.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>

3在junit进行测试

@Test
public void test05() throws IOException{
SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
SqlSession openSession = sqlSessionFactory.openSession();
try{
EmployeeMapperPlus mapper = openSession.getMapper(EmployeeMapperPlus.class);
Employee employee = mapper.getEmpByIdStep(4);
System.out.println(employee);
System.out.println(employee.getDept());
}finally{
openSession.close();
}
}

结果如下：

@Test
public void test05() throws IOException{
SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
SqlSession openSession = sqlSessionFactory.openSession();
try{
EmployeeMapperPlus mapper = openSession.getMapper(EmployeeMapperPlus.class);
Employee employee = mapper.getEmpByIdStep(1);
System.out.println(employee);
System.out.println(employee.getDept());
}finally{
openSession.close();
}
}

结果如下：