mybatis 之 mybatis中查询

1. Mybatis 中又3种查询 seleteOne, seleteList, seleteMap.
2. SeleteOne 查询单个对象：

   映射文件：

   <!-- 根据id查询 -->
       <select id="findById" parameterType="int" resultType="cn.wh.vo.Role">
           select * from t_role where id = #{id}
       </select>
       <select id="totalCount" resultType="int">
           select count(*) from t_role
       </select>

   测试

   //查询单个
       @Test
       public void testSelectOne(){
           Role role = (Role)session.selectOne("cn.wh.mapper.RoleMapper.findById",1);
           System.out.println(role.getName());
       }
       //查询count
       @Test
       public void testSelectCount(){
           Integer count = (Integer)session.selectOne("cn.wh.mapper.RoleMapper.totalCount");
           System.out.println(count);
       }

    

3. selectList  查询结果集：
   

   //查询所有
       @Test
       public void testSelectList(){
           List<Role> list = session.selectList("cn.wh.mapper.RoleMapper.findAll");
           for(Role role:list){
               System.out.println(role.getId()+"----"+role.getName());
           }
       }

    

4. selectMap 查询Map集合：

   @Test
       public void testSelectMap(){
           //第二参数是列名  作为 map的key
           Map<Integer,Role> map = session.selectMap("cn.wh.mapper.RoleMapper.findAll", "id");
           Iterator<Integer> iter = map.keySet().iterator();
           while(iter.hasNext()){
               Integer key = iter.next();
               System.out.println(key+"--------"+map.get(key).getName());
           }
       }