1.全局配置文件沒配好？

檢查全局配置文件application.properties或application.yml是否配置掃描mapper包的文件路徑

#mybatis配置mapper文件路徑
#mybatis.mapper-locations=classpath:/mapper/*.xml
#mybatis-plus配置mapper文件路徑
mybatis-plus.mapper-locations=classpath:/mapper/*.xml

2.啟動類沒加包掃描注解 ？

檢查啟動類上是否添加包掃描注解

@SpringBootApplication
@MapperScan("項目路徑.mapper")
public class DormitoryBackendApplication {public static void main(String[] args) {SpringApplication.run(DormitoryBackendApplication.class, args);
}

3.沒使用@Mapper注解？

XXXmapper.java類是否使用@Mapper注解

@Mapper
public interface AttendanceMapper extends BaseMapper<Attendance> {}

4.命名空間不正確？

檢查XXXmapper.xml的命名空間是否正確，是否能跳轉到對應的XXXmapper.java

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.dormitory.dormitory_backend.mapper.AttendanceMapper"></mapper>

5.檢查mybatis-plus和spirngboot版本是否對應