mybatis @Select注解中如何拼写动态sql

package cn.erongcai.hrplatform.dao.demand;

import java.util.List;

import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;

import com.baomidou.mybatisplus.mapper.BaseMapper;

import cn.erongcai.hrplatform.model.demand.DemandComment;

@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>

方法:用script标签包围，然后像xml语法一样书写

package cn.erongcai.hrplatform.dao.demand;

import java.util.List;

import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;

import com.baomidou.mybatisplus.mapper.BaseMapper;

import cn.erongcai.hrplatform.model.demand.DemandComment;

@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);
}