Thanks to you, I was able to contemplate about lock and isolation.
In source code, you implemented the @Transactional annotation in the Repository Interface, but according to Spring documentation, they recommend setting it at the class level.
how do you think about it?
docs.spring.io/spring-framework/reference/data-ac…
---- I discovered this after making the comment ---- It seems that the Repository with Data JPA interface is an exception where it's permissible to use Transactional.