Fix IDEA Mapper Red Errors: Complete Guide

There are several possible reasons why the mapper file in IDEA is showing errors.

1. Dependencies are missing in the project. Please check the project’s dependency configuration to ensure that all dependencies have been correctly added to the pom.xml file.
2. The mapping file path is incorrectly configured. Make sure the path of the mapping file matches the path in the configuration file (such as mybatis-config.xml or application.properties).
3. The mapper interface is not correctly mapped to the corresponding XML file. Verify if the naming of the mapper interface matches the namespace of the XML file, and ensure that the method names in the mapper interface match the IDs in the XML file.
4. There is a syntax error in the SQL statement in the mapper file. Check if the SQL statement in the mapper file is correct, you can try executing the SQL statement in the database client to see if there is a syntax error.
5. Cache issues in IDEA. Try recompiling the project or restarting IDEA to see if the problem can be resolved.

If the above methods are ineffective, you can try deleting the mapper file and recreating it, or try using a different IDE (such as Eclipse) for development. If the problem persists, it may be due to other unknown reasons, and you can try asking for help from other developers in the developer community (such as Stack Overflow).