MyBatis最佳实践:注解开发

1. 注解：

   1. @Insert：添加
   2. @Update：修改
   3. @Delete：删除
   4. @Select：查询
   5. @Result：实现结果集封装
   6. @Results：可以和 @Reslult 一起使用，封装多个结果集
   7. @One：实现一对一和多对一的结果集封装
   8. @Many：实现一对多结果集封装

2. MyBatis 注解不能实现动态SQL 

3. 使用：

   1. SqlMapConfig.xml 配置文件

      <mappers>
          <!-- 第一种方式：class引入接口,只能引入一个接口-->
          <mapper class="com.mybatis.Dao.TeacherDao"/>
          
          <!-- 第二种方法:针对包下边的所用接口-->
          <package name="com.mybatis.Dao"/>
      </mappers>

   2. 编写注解：
      1. 增删改查：

         @Select("select * from user")
         <!--结果映射集  字段和数据库的字段一一对应-->
         @Results(id = "userMap" ,value = {
                 @Result(property = "id",column = "id"),
                 @Result(property = "username",column = "username"),
                 @Result(property = "birthday",column = "birthday"),
                 @Result(property = "sex",column = "sex"),
                 @Result(property = "address",column = "address")
         })
         List<User> findAll();
         
         @Select("select * from user where id = #{id}")
         @ResultMap(value = "userMap")
         List<User> findById(Integer id);
         
         @Select("select * from user where username = #{name}")
         @ResultMap(value = "userMap")
         List<User> findByName(String name);
         
         @Update("update user set username = #{username},birthday = #{birthday},sex = #{sex},address = #{address} where id = #{id}")
         int update(User user);
         
         @Delete("delete from user where  id = #{id}")
         int delete(Integer id);
         
         @Insert("insert into user (username,birthday,sex,address) value(#{username},#{birthday},#{sex},#{address})")
         int insert(User user);

   3. 多对一注解查询：
      1. 立即加载：

         @Select("select student.*,teacher.Tname from student left join teacher on student.t_id = teacher.id")
         @Results(id = "StudentMap",value = {
                 @Result(property = "id",column = "id"),
                 @Result(property = "Sname",column = "Sname"),
                 @Result(property = "sex",column = "sex"),
                 @Result(property = "age",column = "age"),
                 @Result(property = "t_id",column = "t_id"),
                 @Result(property = "teacher.Tname",column = "Tname")
         })
         List<Student> SelectStudentTeacher();

      2. 延迟加载：

         @Select("select * from student")
         @Results(id = "StudentMap",value = {
                 @Result(property = "id",column = "id"),
                 @Result(property = "Sname",column = "Sname"),
                 @Result(property = "sex",column = "sex"),
                 @Result(property = "age",column = "age"),
                 @Result(property = "t_id",column = "t_id"),
                 @Result(property = "teacher",column = "t_id",one = @One(select = "com.mybatis.Dao.TeacherDao.findTeacherById"))
         })
         List<Student> SelectStudentTeacher();
         
         //teacherDao接口
         @Select("select * from teacher where id = #{t_id}")
         List<Teacher> findTeacherById(Integer t_id);

      3. 一对多注解查询：

         @Select("select * from teacher")
         @Results(id = "teacherMap",value = {
                 @Result(property = "id",column = "id"),
                 @Result(property = "Tname",column = "Tname"),
                 @Result(property = "student",column = "id",
                         many = @Many(select = "com.mybatis.Dao.StudentDao.selectStudentByTeacherId",
                                 fetchType = FetchType.LAZY))    //延迟加载
         })
         List<Teacher> selectTeacherStudent();
         
         
         //studentDao接口
         @Select("select * from student where t_id = #{id}")
         List<Student> selectStudentByTeacherId(Integer id);