17、mybatis学习——mybatis的动态sql之<choose><when><otherwise>选择唯一条件

StudentMapper接口中定义方法

StudentMapper配置文件进行相应的配置（这里没有写<otherwise>标签，接在<when>标签即可）

      <select id="getStuByChoose" resultType="student">
         select * from student 
         <where>
             <!-- choose选择多种情况中的一种，多种情况符合时选择最前的一种 -->
             <choose>
                 <when test="id!=null">
                     id = #{id}
                 </when>
                 <when test="name!=null &amp;&amp; name.trim()!=''">
                     name = #{name}
                 </when>
             </choose>
         </where>
     </select>

测试1（当只有name值时）

    //测试动态sql的<choose><when><otherwise>
    @Test
    public void testGetStuByChoose() 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.getStuByChoose(new Student(null, "小明"));
        System.out.println(student);
        sqlSession.close();
    }

测试结果

测试2（当id和name都有值时）

    //测试动态sql的<choose><when><otherwise>
    @Test
    public void testGetStuByChoose() 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.getStuByChoose(new Student(1, "小明"));
        System.out.println(student);
        sqlSession.close();
    }

测试结果（因为在<when>中id在前，所以会根据id查询）