mybatis @Select注解中如何拼写动态sql

Posted 2020-11-23 那些年的代码

@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);

　　在这里还碰到一个问题就是报错：Caused by: org.apache.ibatis.reflection.ReflectionException: There is no getter for property named ‘status‘ in ‘class java.lang.Interger‘

　　出现原因：这里出现的问题是在DAO方法中定义的参数 与 实体中定义的属性不一致 导致的。

　　解决方案：dao层加@Param("userId")注解即可（实例中就是加上@Param("status")）

　　public List<DictItem> selectKeyByUserId(@Param("userId") long userId);