mybatis之注意事项

不支持Mapper方法重载

1. 从源码可以看出mybatis是通过 全限定名.方法名 来作为唯一的命名的，所以同名的方法是会抛异常的

   public interface UserMessageMapper {
   
       public UserMessage findUserMessageById(Long id);
   
       public UserMessage findUserMessageById(String mobileNoInternet);
   }
   <select id="findUserMessageById" resultMap="userMessageBaseMap">
           select <include refid="userMessageColumns" /> from t_user_message t where t.id=#{id};
       </select>
   
       <select id="findUserMessageById" resultMap="userMessageBaseMap">
           select <include refid="userMessageColumns" /> from t_user_message t where t.mobile_no_internet=#{mobileNoInternet};
       </select>
   
       @Test
       public void testFindUserMessageIdForMapper(){
           String resource = "Configuration.xml";
           InputStream is = UserMessageTest.class.getClassLoader().getResourceAsStream(resource);
           SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is);
           SqlSession session = sessionFactory.openSession();
           UserMessageMapper userMessageMapper = session.getMapper(UserMessageMapper.class);
           UserMessage userMessage = userMessageMapper.findUserMessageById(7777L);
           System.out.println(userMessage);
       }
       @Test
       public void testFindUserMessageIdForMapper2(){
           String resource = "Configuration.xml";
           InputStream is = UserMessageTest.class.getClassLoader().getResourceAsStream(resource);
           SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is);
           SqlSession session = sessionFactory.openSession();
           UserMessageMapper userMessageMapper = session.getMapper(UserMessageMapper.class);
           UserMessage userMessage = userMessageMapper.findUserMessageById("15210321876");
           System.out.println(userMessage);
       }

Mybatis更新值为0问题

1. mybatis

   mybatis中，如果更新字段类型为Long或Integer，将更新该字段值为0时，if条件遇0则会判断为false，值会更新不成功；
   解决方法：
   判断值是否为空写为这种方式：<if test="(testvalue!=null and testvalue!='') or testvalue==0"></if>

常用语句

1. 数组参数查询

   public List<Role> findRoleByIds(Long[] roleId);
   
   <select id="findRoleByIds" resultMap="roleBaseMap">
   SELECT tr.* FROM t_role tr WHERE tr.`id` in
              <foreach item="item" index="index"  collection="array" open="("separator="," close=")"> 
                    #{item} 
              </foreach>
   </select>

2. Like查询

   使用函数拼接CONCAT(CONCAT('%', #{roleName}),'%')
   <select id="findRoleListByPage" parameterType="java.util.Map" resultMap="roleBaseMap">
     select
       <include refid="roleColumns"/>
      from  t_role
      <if test="roleName!=null">
         where role_name like CONCAT(CONCAT('%', #{roleName}),'%')
      </if>
      order by role_name
   </select>

3. 数组+其他参数混合

   • 批量更新

      public int updateReadBatch(@Param("userId")Long userId,@Param("msgIds") Long[] msgIds);
     
      <update id="updateReadBatch">
         <foreach collection="msgIds" item="item" index="index" open="" close="" separator=";">
             update t_user_message SET read_status=0 where  user_id = #{userId} and id  =#{item}
         </foreach>
      </update>

   • 批量删除

     public int deleteBatch(@Param("userId")Long userId,@Param("msgIds") Long[] msgIds);
     
     
     <!--删除消息，设置为无效状态  -->
     <delete id="deleteBatch">
     <foreach collection="msgIds" item="item" index="index" open="" close="" separator=";">
         update t_user_message SET status=0 where  user_id = #{userId} and id  =#{item}
         </foreach>
     </delete>