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背景

在业务中我们在前端总是需要展示数据，将后端得到的数据进行分页处理，通过pagehelper实现动态的分页查询，将查询页数和分页数通过前端发送到后端，后端使用pagehelper，底层是封装threadlocal得到页数和分页数并动态的拼接到sql中完成分页的查询

代码

菜品的分页查询展示
前端传递对象

@Data
public class DishPageQueryDTO implements Serializable {private int page;private int pageSize;private String name;//分类idprivate Integer categoryId;//状态 0表示禁用 1表示启用private Integer status;}

controller层

/*** 菜品分页查询** @param dishPageQueryDTO* @return*/@GetMapping("/page")@ApiOperation("菜品分页查询")public Result<PageResult> page(DishPageQueryDTO dishPageQueryDTO) {PageResult pageResult = dishService.pageQuery(dishPageQueryDTO);return Result.success(pageResult);}

service层

PageResult pageQuery(DishPageQueryDTO dishPageQueryDTO);

public PageResult pageQuery(DishPageQueryDTO dishPageQueryDTO) {PageHelper.startPage(dishPageQueryDTO.getPage(), dishPageQueryDTO.getPageSize());Page<DishVO> page = dishMapper.pageQuery(dishPageQueryDTO);return new PageResult(page.getTotal(), page.getResult());}

将封装好的需要查询的页面和页面大小传给PageHelper，由它为我们动态的拼接到SQL语句中实现分页查询的效果
Mapper层

Page<DishVO> pageQuery(DishPageQueryDTO dishPageQueryDTO);

 <select id="pageQuery" resultType="com.sky.vo.DishVO">select d.* , c.name as categoryName from dish d left outer join category c on d.category_id = c.id<where><if test="name != null">and d.name like concat('%',#{name},'%')</if><if test="categoryId != null">and d.category_id = #{categoryId}</if><if test="status != null">and d.status = #{status}</if></where>order by d.create_time desc</select>