解析MyBatisPlus解决逻辑删除与唯一索引的兼容问题

create unique index uni_username on user(username)

create unique index uni_username_deleted on user(username,deleted)

【强制】业务上具有唯一特性的字段，即使是组合字段，也必须建成唯一索引。

即使在应用层做了非常完善的校验和控制，只要没有唯一索引，根据墨菲定律，必然有脏数据产生。

我们依旧可以将 username + deleted 组合成一个联合唯一索引,但是删除的时候deleted不再是固定的1，而是当前的主键ID,也就是deleted不等于0都是删除状态，如果删除了那deleted值=id值

  
    @TableLogic(value = "0", delval = "1")
    private Integer deleted;

    @TableLogic(value = "0", delval = "id")
    private Integer deleted;

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)

CREATE TABLE `user` (
  `id` int unsigned  AUTO_INCREMENT COMMENT '主键',
  `username` varchar(128)  COMMENT '用户名',
  `phone` varchar(32)  COMMENT '手机号',
  `sex` char(1)  COMMENT '性别',
  `create_time` datetime  COMMENT '创建时间',
  `update_time` datetime  COMMENT '更新时间',
  `deleted` tinyint DEFAULT '0' COMMENT '1、删除 0、未删除',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 

@Data
@Accessors(chain = true)
@TableName("user")
public class UserDO implements Serializable {

    private static final long serialVersionUID = 1L;

    @TableId(type = IdType.AUTO)
    private Integer id;
    
    private String username;
    
    private String phone;
    
    private String sex;
    
    private LocalDateTime createTime;
    
    private LocalDateTime updateTime;

    
    private Integer deleted;
}

    @Test
    public void deleteById() {
        //方式一:根据id删除
        mapper.deleteById(10);
        //方式二:根据指定字段删除
        LambdaQueryWrapper<UserDO> wrapper = new LambdaQueryWrapper<>();
        wrapper.eq(UserDO::getSex, "男");
        mapper.delete(wrapper);
        //方式三:手动逻辑删除
        UserDO userDO = new UserDO();
        userDO.setId(10);
        userDO.setDeleted(1);
        mapper.updateById(userDO);
    }

 @TableLogic(value = "0", delval = "id")
 private Integer deleted;

--方式1
UPDATE user SET deleted=id WHERE id=10 AND deleted=0
--方式2
UPDATE user SET deleted=id WHERE deleted=0 AND (sex = '男')
--方式3
报错了

UPDATE user  WHERE id=?  AND deleted=0

UPDATE user SET deleted=1  WHERE id=?  AND deleted=0

Mybatisplus在updateById更新时，如果已经加了逻辑删除标记,那做SQL拼接的时候,会自动过滤掉逻辑删除的Set拼接