Mybatis 分页插件 PageHelper-编程知识

今天记录下 Mybatis 分页插件 pageHelper 的使用。

背景

有一个员工表(employee)，现在要使用 pageHelper 插件实现员工的分页查询。

员工表

create table employee
(id          bigint auto_increment comment '主键'primary key,name        varchar(32)   not null comment '姓名',username    varchar(32)   not null comment '用户名',password    varchar(64)   not null comment '密码',phone       varchar(11)   not null comment '手机号',sex         varchar(2)    not null comment '性别',id_number   varchar(18)   not null comment '身份证号',status      int default 1 not null comment '状态 0:禁用，1:启用',create_time datetime      null comment '创建时间',update_time datetime      null comment '更新时间',create_user bigint        null comment '创建人',update_user bigint        null comment '修改人',constraint idx_usernameunique (username)
)comment '员工信息' collate = utf8_bin;

实体类

Employee

employee类定义代码如下

package com.sky.entity;import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;import java.io.Serializable;
import java.time.LocalDateTime;@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;}

EmployeeDTO

EmployeeDTO定义代码如下

package com.sky.dto;import lombok.Data;import java.io.Serializable;@Data
public class EmployeeDTO implements Serializable {private Long id;private String username;private String name;private String phone;private String sex;private String idNumber;}

封装类

PageResult

最后返回给前端的数据封装在 PageResult 类中， PageHelper 类定义如下：

/*** 封装分页查询结果*/
@Data
@AllArgsConstructor
@NoArgsConstructor
public class PageResult implements Serializable {//总记录数private long total;//当前页数据集合private List records;}

EmployeePageQueryDTO

分页查询类

@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;}

Result

Result 类为后端统一返回给前端的类型，定义如下：

package com.sky.result;import lombok.Data;import java.io.Serializable;/*** 后端统一返回结果* @param <T>*/
@Data
public class Result<T> implements Serializable {private Integer code; //编码：1成功，0和其它数字为失败private String msg; //错误信息private T data; //数据public static <T> Result<T> success() {Result<T> result = new Result<T>();result.code = 1;return result;}public static <T> Result<T> success(T object) {Result<T> result = new Result<T>();result.data = object;result.code = 1;return result;}public static <T> Result<T> error(String msg) {Result result = new Result();result.msg = msg;result.code = 0;return result;}}

业务实现

Controller 层

定义 EmployeeController

/*** 员工管理*/
@RestController
@RequestMapping("/admin/employee")
@Slf4j
@Api(tags = "员工相关接口")
public class EmployeeController {@Autowiredprivate EmployeeService employeeService;/*** @Description ToDo  员工分页查询* @param employeePageQueryDTO* @return Result<PageResult>*/@GetMapping("/page")@ApiOperation("员工分页查询")public Result<PageResult> page(EmployeePageQueryDTO employeePageQueryDTO){PageResult pageResult = employeeService.pageQuery(employeePageQueryDTO);return Result.success(pageResult);}
}

Service 层

@Service
public class EmployeeServiceImpl implements EmployeeService {@Autowiredprivate EmployeeMapper employeeMapper;@Overridepublic PageResult pageQuery(EmployeePageQueryDTO employeePageQueryDTO) {/**select * from employee limit start, pageSize传统方法时需要手动计算 start 和 pageSize 的值，这里可以直接通过startPage方法很方便的实现该功能。*/PageHelper.startPage(employeePageQueryDTO.getPage(), employeePageQueryDTO.getPageSize());// 这里要返回 Page 类，泛型类型是对应的要返回的实体类，这里是 Employee，包含数据总条数和所有数据Page<Employee> page = employeeMapper.pageQuery(employeePageQueryDTO);// 将查询到的数据封装到 PageResult 类中PageResult pageResult = new PageResult(page.getTotal(), page.getResult());return pageResult;}
}

Mapper 层

EmployeeMapper

@Mapper
public interface EmployeeMapper {/*** 员工信息分页查询* @param employeePageQueryDTO* @return PageResult*/Page<Employee> pageQuery(EmployeePageQueryDTO employeePageQueryDTO);
}

SQL语句编写

因为这里的 sql 语句较为麻烦，因此使用 xml 方式实现，这里也实现了模糊查询的功能。


<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.sky.mapper.EmployeeMapper"><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>
</mapper>