在学习jsp的时候，我用到了分页，那时候分页对于我来说很难，调试了大半天，不是这错就是那错，如今学了mybatis 和他的插件mybatis-pagehelper觉得分页简单了。
耐心看完，最后有完整的使用案例
1. 引入分页插件的依赖：
<!--pagehelper -->
<
dependency
>
<
groupId
>
com.github.pagehelper
</
groupId
>
<
artifactId
>
pagehelper-spring-boot-starter
</
artifactId
>
<
version
>
1.2.12
</
version
>
</
dependency
>
2.在.yml文件中添加：
# 分页插件配置
pagehelper:
helperDialect: mysql
supportMethodsArguments: true
3.
使用分页插件，在查询前使用分页插件，原理：统一拦截
sql
，为其提供分页功能：
/**
* page: 第几页
* pageSize: 每页显示条数
* 这两个参数都是由前端传来
*/
PageHelper
.
startPage
(
page
,
pageSize
);
4.
分页数据封装到
PagedGridResult.java 传给前端(
PagedGridResult 是自定义的，但也是通用的，会提供
):
PageInfo
<?>
pageList
=
new
PageInfo
<>
(
list
);
PagedGridResult grid
=
new
PagedGridResult
();
grid
.
setPage
(
page
); // 当前页数
grid
.
setRows
(
list
); //这个list是分页后的数据，是每行的数据
grid
.
setTotal
(
pageList
.
getPages
());
grid
.
setRecords
(
pageList
.
getTotal
());
/*****
看到4 中的代码你可能会迷：
1.PageInfo中的 total 表示： 总记录数 ，而 他的 records才 表示：总记录数
2.PageInfo 中的 page 表示： 总页数，而
PagedGridResult 中的 total 表示 总页数
*/
==================================================================
5.
PagedGridResult 类：
/**
*
* @Title: PagedGridResult.java
* @Package com.imooc.utils
* @Description: 用来返回分页Grid的数据格式
* Copyright: Copyright (c) 2019
*/
public class PagedGridResult {
private int page; // 当前页数
private int total; // 总页数
private long records; // 总记录数
private List<?> rows; // 每行显示的内容
public int getPage() {
return page;
}
public void setPage(int page) {
this.page = page;
}
public int getTotal() {
return total;
}
public void setTotal(int total) {
this.total = total;
}
public long getRecords() {
return records;
}
public void setRecords(long records) {
this.records = records;
}
public List<?> getRows() {
return rows;
}
public void setRows(List<?> rows) {
this.rows = rows;
}
}
========================================================================
6. 使用案例：
@Transactional(propagation = Propagation.SUPPORTS)
@Override
public PagedGridResult queryPagedComments(String itemId, Integer level,
Integer page,Integer pageSize) {
Map<String,Object>map =new HashMap<>();
map.put("itemId",itemId);
map.put("level",level);
/*** page: 第几页 * pageSize: 每页显示条数 */
PageHelper.startPage(page, pageSize);
List<ItemCommentVO> list=itemsMapperCustom.queryItemComments(map);
PageInfo<?> pageList = new PageInfo<>(list); //<>中就是 ？ ，不是乱码，可以传任何类
PagedGridResult grid = new PagedGridResult();
grid.setPage(page);
grid.setRows(list);
grid.setTotal(pageList.getPages());
grid.setRecords(pageList.getTotal());
return grid;
}
================================================================================
7.如果你有很多地方要用到分页，也可以将其抽取出来：
@Transactional(propagation = Propagation.SUPPORTS)
@Override
public PagedGridResult queryPagedComments(String itemId, Integer level,
Integer page,Integer pageSize) {
Map<String,Object>map =new HashMap<>();
map.put("itemId",itemId);
map.put("level",level);
/*** page: 第几页 * pageSize: 每页显示条数 */
PageHelper.startPage(page, pageSize);
List<ItemCommentVO> list=itemsMapperCustom.queryItemComments(map);
return setterPagedGrid(list,page);
}
private PagedGridResult setterPagedGrid(List<?>list,Integer page){
PageInfo<?> pageList = new PageInfo<>(list);
PagedGridResult grid = new PagedGridResult();
grid.setPage(page);
grid.setRows(list);
grid.setTotal(pageList.getPages());
grid.setRecords(pageList.getTotal());
return grid;
}
pageHelper 不支持 嵌套分页，会出现一些问题：
关于订单有三张表：订单表，订单状态表，订单关联商品表
比如说：查询订单信息，一个订单对应多个商品，这种情况:
不用分页一般是用一条sql语句：
od.id as orderId,
od.created_time as createdTime,
od.pay_method as payMethod,
od.real_pay_amount as realPayAmount,
od.post_amount as postAmount,
os.order_status as orderStatus,
oi.item_id as itemId,
oi.item_name as itemName,
oi.item_img as itemImg,
oi.item_spec_name as itemSpecName,
oi.buy_counts as buyCounts,
oi.price as price
FROM
orders od
LEFT JOIN
order_status os
on od.id = os.order_id
LEFT JOIN
order_items oi
ON od.id = oi.order_id
WHERE
od.user_id = #{paramsMap.userId}
AND
od.is_delete = 0
<if test="paramsMap.orderStatus != null">
and os.order_status = #{paramsMap.orderStatus}
</if>
ORDER BY
od.updated_time ASC
但是对于分页就不行了，
如何解决呢？答：先查询订单信息（order 和order_status先关联），再根据订单信息中的orderId 来查询对应的商品关联信息
resultMap中的collection中配置的select传递条件
<resultMap id="myOrdersVO" type="com.imooc.pojo.vo.MyOrdersVO">
<id column="orderId" property="orderId"/>
<result column="createdTime" property="createdTime"/>
<result column="payMethod" property="payMethod"/>
<result column="realPayAmount" property="realPayAmount"/>
<result column="postAmount" property="postAmount"/>
<result column="orderStatus" property="orderStatus"/>
<result column="isComment" property="isComment"/>
<collection property="subOrderItemList"
select="getSubItems"
column="orderId"
ofType="com.imooc.pojo.vo.MySubOrderItemVO">
<result column="itemId" property="itemId"/>
<result column="itemName" property="itemName"/>
<result column="itemImg" property="itemImg"/>
<result column="itemSpecId" property="itemSpecId"/>
<result column="itemSpecName" property="itemSpecName"/>
<result column="buyCounts" property="buyCounts"/>
<result column="price" property="price"/>
</collection>
</resultMap>
============================================================
<select id="queryMyOrders" resultMap="myOrdersVO" parameterType="Map">
SELECT
od.id as orderId,
od.created_time as createdTime,
od.pay_method as payMethod,
od.real_pay_amount as realPayAmount,
od.post_amount as postAmount,
os.order_status as orderStatus,
od.is_comment as isComment
FROM
orders od
LEFT JOIN
order_status os
on od.id = os.order_id
WHERE
od.user_id = #{paramsMap.userId}
AND
od.is_delete = 0
<if test="paramsMap.orderStatus != null">
and os.order_status = #{paramsMap.orderStatus}
</if>
ORDER BY
od.updated_time ASC
</select>
========================================================
<select id="getSubItems" parameterType="String" resultType="com.imooc.pojo.vo.MySubOrderItemVO">
select
oi.item_id as itemId,
oi.item_name as itemName,
oi.item_img as itemImg,
oi.item_spec_name as itemSpecName,
oi.buy_counts as buyCounts,
oi.price as price
from
order_items oi
where
oi.order_id = #{orderId}
</select>
