MyBatis-Plus实现分页的方法使用详解

简介

本文介绍MyBatis-Plus的分页的方法。

包括：

• 不传参数时的默认结果

• 查询不存在的数据

• 手动包装page

• 自定义SQL

建库建表

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);

依赖

<?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>

配置

application.yml

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

分页插件配置（必须）

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;
   }
}

代码

Entity

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;
}

Mapper

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);
}

Service

接口

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> {
}

实现

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 {
}

Controller

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);
   }
}

测试

访问knife4j：http://localhost:8080/doc.html

1. 不传参数

2. 查不存在的数据

3. 手动包装

4. 自定义SQL

来源：https://blog.csdn.net/feiying0canglang/article/details/123642286