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MyBatis-Plus–解决逻辑删除与唯一索引的问题

简介

说明

本文用示例介绍MyBatis-Plus如何解决逻辑删除与唯一索引的问题。

物理删除与逻辑删除

数据是很重要的,数据库里的数据在删除时一般不会用DELETE语句直接物理删除。

通常的做法是使用逻辑删除,也就是:新加一个标记是否删除的字段,在删除时不是真的删除,而是使用UPDATE语句将某个字段设置为删除状态。例如:”deleted_flag”,0表示未删除,其他表示已删除。

MyBatis-Plus默认的逻辑删除

MyBatis-Plus里可以将某个字段标记为逻辑删除字段,方法是:在字段上加@TableLogic注解:

@TableLogic
private Long deletedFlag;

这样一来,操作数据时会自动操作:

  • 查询时:自动加”AND deletedFlag = 0″
  • 删除时:UPDATE SET deletedFlag = 1 … WHERE … AND deleted_flag = 0

其默认的全局配置为:

mybatis-plus:
  global-config:
    db-config:
      logic-delete-value: 1 # 逻辑已删除值(默认为 1)
      logic-not-delete-value: 0 # 逻辑未删除值(默认为 0)

MyBatis-Plus默认逻辑删除的问题

假设有一张用户表,有user_name和deleted_flag字段,想给user_name加唯一索引(提高查询速度、确保用户名不重复),这时有如下两种方案:

  1. 将user_name设置为唯一索引
    1. 这样是不行的,比如:有个用户名为“Tony”,删除了,又有一个用户注册,注册为“Tony”,这就会报错。报错的信息是这样的:Duplicate entry ‘Tony’ for key ‘t_user.index_user_name’
  2. 将user_name和deleted_flag设置为联合唯一索引
    1. 这样也是不行的,比如:
      1. 有个用户名为“Tony”,删除了,这样联合索引为“Tony-1”。
      2. 又有一个用户注册,注册为“Tony”,这不会报错,此时新用户联合索引为“Tony-0”
      3. 新用户删除,会报错:因为此时新用户联合索引为“Tony-1”,数据库已经有了。报错的信息是这样的:Duplicate entry ‘Tony-1’ for key ‘t_user.index_user_name_deleted_flag’

问题复现

测试

打开测试页面:http://localhost:8080/doc.html

1. 查看原始数据

2. 删除user_name为“sky”的数据

数据库结果(成功删除)

后端结果

==>  Preparing: UPDATE t_user SET deleted_flag=1 WHERE id=? AND deleted_flag=0 
==> Parameters: 2(Long)
<==    Updates: 1

3. 添加user_name为“sky”的数据

数据库结果(添加成功)

后端结果(添加成功)

==>  Preparing: INSERT INTO t_user ( user_name ) VALUES ( ? ) 
==> Parameters: sky(String)
<==    Updates: 1

4. 删除user_name为“sky”的数据

数据库结果(删除失败)

后端结果(删除失败)

2022-03-20 16:46:09.895 ERROR 15904 --- [nio-8080-exec-7] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.dao.DuplicateKeyException: 
### Error updating database.  Cause: java.sql.SQLIntegrityConstraintViolationException: Duplicate entry 'sky-1' for key 't_user.index_user_name_deleted_flag'
### The error may exist in com/example/demo/user/mapper/UserMapper.java (best guess)
### The error may involve com.example.demo.user.mapper.UserMapper.deleteById-Inline
### The error occurred while setting parameters
### SQL: UPDATE t_user SET deleted_flag=1 WHERE id=?  AND deleted_flag=0
### Cause: java.sql.SQLIntegrityConstraintViolationException: Duplicate entry 'sky-1' for key 't_user.index_user_name_deleted_flag'
; Duplicate entry 'sky-1' for key 't_user.index_user_name_deleted_flag'; nested exception is java.sql.SQLIntegrityConstraintViolationException: Duplicate entry 'sky-1' for key 't_user.index_user_name_deleted_flag'] with root cause

java.sql.SQLIntegrityConstraintViolationException: Duplicate entry 'sky-1' for key 't_user.index_user_name_deleted_flag'
	at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:117) ~[mysql-connector-java-8.0.20.jar:8.0.20]
	at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97) ~[mysql-connector-java-8.0.20.jar:8.0.20]
	at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122) ~[mysql-connector-java-8.0.20.jar:8.0.20]
	...
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_201]
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.36.jar:9.0.36]
	at java.lang.Thread.run(Thread.java:748) [na:1.8.0_201]

代码

依赖

pom.xml

<?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>2.3.1.RELEASE</version>
<!--        <version>2.0.0.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>3.3.2</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>

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);

Java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
    private Long deletedFlag;
}

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> {
}

实现类

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.example.demo.user.entity.User;
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.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@Api(tags = "测试")
@RestController
@RequestMapping("test")
public class TestController {

    @Autowired
    private UserService userService;

    @ApiOperation("删除")
    @PostMapping("delete")
    public String delete(Long id) {
        userService.removeById(id);
        return "remove success";
    }

    @ApiOperation("添加")
    @PostMapping("add")
    public User add() {
        User user = new User();
        user.setUserName("sky");
        userService.save(user);
        return user;
    }
}

解决方案

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1

评论2

请先

  1. logic-delete-value="id" 这样是不是就可以了,不用每个实体对象都在注解上加 delval = "NOW()"
    老安 2023-10-24 0
    • 是的。不过你可能打错了,logic-delete-value="id' 等价于所有注解上加 delval = "id", logic-delete-value="NOW()" 等价于所有注解上加 delval = "NOW()",
      自学精灵 2023-10-24 0
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