pagehelper分页查询
PageHelper是MyBatis框架中提供的分页插件，它支持Oracle、Mysql、MariaDB、SQLite、Hsqldb、PostgreSQL六种数据库。使用PageHelper可以方便地进行分页查询，只需在SQL查询前调用PageHelper.startPage方法并传入两个参数：page=页码，rows=每页显示的条数。例如，PageHelper.startPage(1, 20)表示请求第一页，每页显示20条数据。
1.pom文件
引入 pagehelper pom文件
<dependency><groupId>com.github.pagehelper</groupId><artifactId>pagehelper-spring-boot-starter</artifactId></dependency>
2.Controller
控制层接收到"/page"请求，传递到后台参数封装为了EmployeePageQueryDTO对象
调用service层
/*** 员工分页查询* @param employeePageQueryDTO* @return*/@GetMapping("/page")@ApiOperation("员工分页查询")public Result<PageResult> page(EmployeePageQueryDTO employeePageQueryDTO) {log.info("员工分页查询,参数为: {}", employeePageQueryDTO);PageResult pageResult = employeeService.pageQuery(employeePageQueryDTO);return Result.success(pageResult);}
2.PageResult
封装的分页查询结果
/*** 封装分页查询结果*/
@Data
@AllArgsConstructor
@NoArgsConstructor
public class PageResult implements Serializable {private long total; //总记录数private List records; //当前页数据集合
}
3.EmployeePageQueryDTO
封装的前台传递过来的数据
@Data
public class EmployeePageQueryDTO implements Serializable {//员工姓名private String name;//页码private int page;//每页显示记录数private int pageSize;
}
4.Service
/*** 分页查询* @param employeePageQueryDTO* @return*/PageResult pageQuery(EmployeePageQueryDTO employeePageQueryDTO);
5.ServiceImpl
调用PageHelper方法进行分页查询
需要两个参数 页码，和每一页展示的数量个数
/*** 分页查询* @param employeePageQueryDTO* @return*/public PageResult pageQuery(EmployeePageQueryDTO employeePageQueryDTO) {//开始分页查询PageHelper.startPage(employeePageQueryDTO.getPage(), employeePageQueryDTO.getPageSize());Page<Employee> page = employeeMapper.pageQuery(employeePageQueryDTO);long total = page.getTotal();List<Employee> result = page.getResult();return new PageResult(total, result);}
6.Employee
员工的实体类
@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
public class Employee implements Serializable {private static final long serialVersionUID = 1L;private Long id;private String username;private String name;private String password;private String phone;private String sex;private String idNumber;private Integer status;//@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss")private LocalDateTime createTime;//@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss")private LocalDateTime updateTime;private Long createUser;private Long updateUser;
}
7.mapper
/*** 分页查询* @param employeePageQueryDTO* @return*/Page<Employee> pageQuery(EmployeePageQueryDTO employeePageQueryDTO);
8.mapper.xml
PageHelper会自动的补全sql代码
<select id="pageQuery" resultType="com.sky.entity.Employee">select * from employee<where><if test="name != null and name != ''">and name like concat('%',#{name},'%')</if></where>order by create_time desc</select>
控制台输出记录2023-10-10 22:37:55.033 INFO 18988 --- [nio-8080-exec-5] c.s.controller.admin.EmployeeController : 员工分页查询,参数为: EmployeePageQueryDTO(name=null, page=1, pageSize=10)
2023-10-10 22:37:55.239 DEBUG 18988 --- [nio-8080-exec-5] c.s.m.EmployeeMapper.pageQuery_COUNT : ==> Preparing: SELECT count(0) FROM employee
2023-10-10 22:37:55.240 DEBUG 18988 --- [nio-8080-exec-5] c.s.m.EmployeeMapper.pageQuery_COUNT : ==> Parameters:
2023-10-10 22:37:55.246 DEBUG 18988 --- [nio-8080-exec-5] c.s.m.EmployeeMapper.pageQuery_COUNT : <== Total: 12023-10-10 22:37:55.250 DEBUG 18988 --- [nio-8080-exec-5] com.sky.mapper.EmployeeMapper.pageQuery : ==> Preparing: select * from employee order by create_time desc LIMIT ?//这里显示了 自动补全的代码LIMIT2023-10-10 22:37:55.252 DEBUG 18988 --- [nio-8080-exec-5] com.sky.mapper.EmployeeMapper.pageQuery : ==> Parameters: 10(Integer)
2023-10-10 22:37:55.256 DEBUG 18988 --- [nio-8080-exec-5] com.sky.mapper.EmployeeMapper.pageQuery : <== Total: 4
