Mybatis @Select注解中如何拼写动态sql

迷南。 2022-02-22 16:44 183阅读 0赞

@Mapper
    public interface DemandCommentMapper extends BaseMapper<DemandComment>{ 
        @Select("SELECT "
                + "a.id as 'id',a.create_date as 'createDate',a.content as 'content',"
                + "a.parent_id as 'parentId',a.first_comment_id as 'firstCommentId',"
                + "b.id as 'fromUser.id',b.realname as 'fromUser.realname',b.avatar as 'fromUser.avatar',"
                + "c.id as 'toUser.id',c.realname as 'toUser.realname',c.avatar as 'toUser.avatar' "
                + "FROM t_demand_comment a "
                + "LEFT JOIN t_user b ON b.id = a.from_uid "
                + "LEFT JOIN t_user c ON c.id = a.to_uid "
                + "WHERE a.demand_id = #{demandId} "
                + "ORDER BY a.create_date ASC"
                + "LIMIT #{startNo},#{pageSize}")
        public List<DemandComment> listDemandComment(@Param("demandId") Long demandId, 
    　　　　　　　　　　　　　　　　　　　　　　　　　　　　　@Param("startNo") Integer pageNo, 
    　　　　　　　　　　　　　　　　　　　　　　　　　　　　　@Param("pageSize") Integer pageSize);

这样整个语句是写死的，如果我想根据pageNo与pageSize是否为空来判断是否需要分页，该怎么做呢?  
如果使用xml来配置的话可以用:

<when test='startNo!=null and pageSize != null '>
      LIMIT #{startNo},#{pageSize}
    </when>

如果是用@Select 这种该如何做呢？

### 方法：用script标签包围，然后像xml语法一样书写 ###

@Mapper
    public interface DemandCommentMapper extends BaseMapper<DemandComment>{ 
        @Select("<script>"
                + "SELECT "
                + "a.id as 'id',a.create_date as 'createDate',a.content as 'content',"
                + "a.parent_id as 'parentId',a.first_comment_id as 'firstCommentId',"
                + "b.id as 'fromUser.id',b.realname as 'fromUser.realname',b.avatar as 'fromUser.avatar',"
                + "c.id as 'toUser.id',c.realname as 'toUser.realname',c.avatar as 'toUser.avatar' "
                + "FROM t_demand_comment a "
                + "LEFT JOIN t_user b ON b.id = a.from_uid "
                + "LEFT JOIN t_user c ON c.id = a.to_uid "
                + "WHERE a.demand_id = #{demandId} "
                + "ORDER BY a.create_date ASC "
                + "<if test='startNo!=null and pageSize != null '>"
                + "LIMIT #{startNo},#{pageSize}"
                + "</if>"
                + "</script>")
        public List<DemandComment> listDemandComment(@Param("demandId") Long demandId, 
    　　　　　　　　　　　　　　　　　　　　　　　　　　　　　@Param("startNo") Integer pageNo, 
    　　　　　　　　　　　　　　　　　　　　　　　　　　　　　@Param("pageSize") Integer pageSize);

### 项目实例 ###

@Select("<script>"
                +"select * from mi_taobao where 1=1"
                +"<if test='status != null'>"
                +"and status = #{status}"
                +"</if>"
                +"</script>")
        public List<Taobao> getTaobao(@Param("status") Integer status);

转载自:[https://blog.csdn.net/qq\_32786873/article/details/78297551][https_blog.csdn.net_qq_32786873_article_details_78297551]

[https_blog.csdn.net_qq_32786873_article_details_78297551]: https://blog.csdn.net/qq_32786873/article/details/78297551