15、mybatis学习——鉴别器discriminator的使用

这个例子只是重在为了理解discriminator的使用

一对多的实体类Student.java

多对一的实体类College.java

StudentMapper接口定义测试discriminator的方法

StudentMapper的sql配置文件中进行相对应接口方法配置

     <!-- 测试鉴别器discriminator -->
     <resultMap type="com.pxxy.bean.Student" id="discriminatorMap">
         <id column="id" property="id"/>
         <result column="name" property="name"/>
         <!-- column：指定通过哪列进行鉴别
             javaType：指定该列是什么类型 -->
         <discriminator javaType="string" column="name">
             <!--value：指该列的值是什么时
              此例是如果是名字是小红时把她的学校信息也查询 -->
             <case value="小红" resultType="student">
                 <association property="college" 
                     select="com.pxxy.bean.CollegeMapper.getColById"
                     column="c_id">
                 </association>
             </case>
         </discriminator>
     </resultMap>
     <select id="discriminatorTest" resultMap="discriminatorMap">
         select * from student where id=#{id}
     </select>

测试方法

    //测试根据学校id分布查询学校以及学校的学生
    @Test
    public void testDiscriminatorTest() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class);
        Student student = studentMapper.discriminatorTest(1);
        System.out.println(student);
        System.out.println(student.getCollege());
        sqlSession.close();
    }