MyBatis-Plus实现分页的方法使用详解

DROP DATABASE IF EXISTS mp;
CREATE DATABASE mp DEFAULT CHARACTER SET utf8;
USE mp;
 
DROP TABLE IF EXISTS `t_user`;
SET NAMES utf8mb4;
 
CREATE TABLE `t_user`
(
    `id`           BIGINT(0) NOT NULL AUTO_INCREMENT,
    `user_name`    VARCHAR(64) NOT NULL COMMENT '用户名（不能重复）',
    `nick_name`    VARCHAR(64) NULL COMMENT '昵称（可以重复）',
    `email`        VARCHAR(64) COMMENT '邮箱',
    `create_time`  DATETIME(0) NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',
    `update_time`  DATETIME(0) NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '修改时间',
    `deleted_flag` BIGINT(0) NOT NULL DEFAULT 0 COMMENT '0：未删除 其他：已删除',
    PRIMARY KEY (`id`) USING BTREE,
    UNIQUE KEY `index_user_name_deleted_flag` (`user_name`, `deleted_flag`),
    KEY `index_create_time`(`create_time`)
) ENGINE = InnoDB COMMENT = '用户';
 
INSERT INTO `t_user` VALUES (1, 'knife', '刀刃', 'abc@qq.com', '2021-01-23 09:33:36', '2021-01-23 09:33:36', 0);
INSERT INTO `t_user` VALUES (2, 'sky', '天蓝', '123@qq.com', '2021-01-24 18:12:21', '2021-01-24 18:12:21', 0);

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.3.12.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>MyBatis-Plus_Simple</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>MyBatis-Plus_Simple</name>
    <description>Demo project for Spring Boot</description>
 
    <properties>
        <java.version>1.8</java.version>
    </properties>
 
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
 
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.5.1</version>
        </dependency>
 
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
 
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>
 
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>
 
        <dependency>
            <groupId>com.github.xiaoymin</groupId>
            <artifactId>knife4j-spring-boot-starter</artifactId>
            <version>3.0.3</version>
        </dependency>
 
    </dependencies>
 
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
 
</project>

spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://127.0.0.1:3306/mp?characterEncoding=UTF-8&serverTimezone=Asia/Shanghai
    username: root
    password: 222333
 
#mybatis-plus配置控制台打印完整带参数SQL语句
mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl

package com.example.demo.config;
 
import com.baomidou.mybatisplus.annotation.DbType;
import com.baomidou.mybatisplus.extension.plugins.MybatisPlusInterceptor;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor;
 
@Configuration
public class MyBatisPlusConfig {
 
    /**
     * 分页插件
     */
    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor() {
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
        return interceptor;
    }
}

package com.example.demo.user.entity;
 
import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableLogic;
import com.baomidou.mybatisplus.annotation.TableName;
import com.baomidou.mybatisplus.extension.activerecord.Model;
import lombok.Data;
 
import java.time.LocalDateTime;
 
@Data
@TableName(value = "t_user")
public class User {
    @TableId(value = "id", type = IdType.AUTO)
    private Long id;
 
    /**
     * 用户名（不能重复）
     */
    private String userName;
 
    /**
     * 昵称（可以重复）
     */
    private String nickName;
 
    /**
     * 邮箱
     */
    private String email;
 
    /**
     * 创建时间
     */
    private LocalDateTime createTime;
 
    /**
     * 修改时间
     */
    private LocalDateTime updateTime;
 
    /**
     * 0：未删除 其他：已删除
     */
    @TableLogic(delval = "id")
    private Long deletedFlag;
}

package com.example.demo.user.mapper;
 
import com.baomidou.mybatisplus.core.conditions.Wrapper;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.core.toolkit.Constants;
import com.example.demo.user.entity.User;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;
import org.springframework.stereotype.Repository;
 
@Repository
public interface UserMapper extends BaseMapper<User> {
    @Select("SELECT * FROM t_user ${ew.customSqlSegment}")
    IPage<User> findUser(IPage<User> page, @Param(Constants.WRAPPER) Wrapper wrapper);
}

package com.example.demo.user.service;
 
import com.baomidou.mybatisplus.extension.service.IService;
import com.example.demo.user.entity.User;
 
public interface UserService extends IService<User> {
}

package com.example.demo.user.service.impl;
 
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.example.demo.user.entity.User;
import com.example.demo.user.mapper.UserMapper;
import com.example.demo.user.service.UserService;
import org.springframework.stereotype.Service;
 
@Service
public class UserServiceImpl extends ServiceImpl<UserMapper, User> implements UserService {
}

package com.example.demo.user.controller;
 
import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.core.toolkit.Wrappers;
import com.baomidou.mybatisplus.extension.conditions.query.LambdaQueryChainWrapper;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.example.demo.user.entity.User;
import com.example.demo.user.mapper.UserMapper;
import com.example.demo.user.service.UserService;
import io.swagger.annotations.Api;
import io.swagger.annotations.ApiOperation;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
 
import java.util.List;
 
@Api(tags = "分页")
@RestController
@RequestMapping("page")
public class PageController {
 
    @Autowired
    private UserService userService;
 
    // 我为了简单直接注入mapper，项目中controller要通过service调mapper
    @Autowired
    private UserMapper userMapper;
 
    @ApiOperation("不传参数")
    @GetMapping("noParam")
    public IPage<User> noParam(Page<User> page) {
        return userService.page(page);
    }
 
    @ApiOperation("查不存在的数据")
    @GetMapping("notExist")
    public IPage<User> notExist(Page<User> page) {
        // 如果查出来为空，会返回入参page里边的数据，比如：current，size等。不需要自己判空。
        return userService.lambdaQuery()
                .eq(User::getUserName, "abcd")
                .page(page);
    }
 
    @ApiOperation("手动包装")
    @GetMapping("manualPack")
    public IPage<User> manualPack(Page<User> page) {
        List<User> skyList = userService.lambdaQuery()
                .eq(User::getUserName, "sky")
                .list();
 
        // 因为Page是IPage的实现类，所以可以直接返回page
        // 也可以自己new 一个Page，然后设置值，不过这样就麻烦了
        return page.setRecords(skyList);
    }
 
    @ApiOperation("自定义SQL")
    @GetMapping("customSQL")
    public IPage<User> customSQLPage(Page<User> page) {
        LambdaQueryWrapper<User> wrapper = Wrappers.lambdaQuery();
        wrapper.eq(User::getUserName, "sky");
 
        // 这样写会报错：MybatisPlusException: can not use this method for "getCustomSqlSegment"
        // LambdaQueryChainWrapper<User> wrapper = userService.lambdaQuery()
        //         .eq(User::getUserName, "sky");
 
        return userMapper.findUser(page, wrapper);
    }
}