mybatis下limit有参数计算时的写法

 开发  mybatis下limit有参数计算时的写法已关闭评论
4月 232020
 

mybatis下limit如果想做分页,对limit做参数计算时:

错误的写法:

<select id=”queryMyApplicationRecord” parameterType=”MyApplicationRequest” resultMap=”myApplicationMap”>
SELECT
a.*,
FROM
tb_user a
WHERE 1=1
<if test=”ids != null and ids.size()!=0″>
AND a.id IN
<foreach collection=”ids” item=”id” index=”index”
open=”(” close=”)” separator=”,”>
#{id}
</foreach>
</if>
<if test=”statusList != null and statusList.size()!=0″>
AND a.status IN
<foreach collection=”statusList” item=”status” index=”index”
open=”(” close=”)” separator=”,”>
#{status}
</foreach>
</if>
ORDER BY a.create_time desc
LIMIT (#{pageNo}-1)*#{pageSize},#{pageSize}; // 错误
</select>
在MyBatis中LIMIT之后的语句不允许的变量不允许进行算数运算,会报错。

正确的写法一:
<select id=”queryMyApplicationRecord” parameterType=”MyApplicationRequest” resultMap=”myApplicationMap”>
SELECT
a.*,
FROM
tb_user a
WHERE 1=1
<if test=”ids != null and ids.size()!=0″>
AND a.id IN
<foreach collection=”ids” item=”id” index=”index”
open=”(” close=”)” separator=”,”>
#{id}
</foreach>
</if>
<if test=”statusList != null and statusList.size()!=0″>
AND a.status IN
<foreach collection=”statusList” item=”status” index=”index”
open=”(” close=”)” separator=”,”>
#{status}
</foreach>
</if>
ORDER BY a.create_time desc
LIMIT ${(pageNo-1)*pageSize},${pageSize}; (正确)
</select>
正确的写法二:(推荐)
<select id=”queryMyApplicationRecord” parameterType=”MyApplicationRequest” resultMap=”myApplicationMap”>
SELECT
a.*,
FROM
tb_user a
WHERE 1=1
<if test=”ids != null and ids.size()!=0″>
AND a.id IN
<foreach collection=”ids” item=”id” index=”index”
open=”(” close=”)” separator=”,”>
#{id}
</foreach>
</if>
<if test=”statusList != null and statusList.size()!=0″>
AND a.status IN
<foreach collection=”statusList” item=”status” index=”index”
open=”(” close=”)” separator=”,”>
#{status}
</foreach>
</if>
ORDER BY a.create_time desc
LIMIT #{offSet},#{limit}; (推荐,代码层可控)
</select>
分析:方法二的写法,需要再请求参数中额外设置两个get函数,如下:
@Data
public class QueryParameterVO {

private List<String> ids;

private List<Integer> statusList;

// 前端传入的页码
private int pageNo; // 从1开始

// 每页的条数
private int pageSize;

// 数据库的偏移
private int offSet;

// 数据库的大小限制
private int limit;

// 这里重写offSet和limit的get方法
public int getOffSet() {
return (pageNo-1)*pageSize;
}

public int getLimit() {
return pageSize;
}
}