Its safe to call .block() on database query/insert result?

[thankusWR]

In my service I have one use cases when synchronous call to database is required and I wonder if I can securely call block() on that result?
Method is called in non-reactive thread so on my tests it works fine but from what heard in some cases its dangerous to call block().

Below is my repository and DB operation on which I want to block.

@Repository
public interface UserRepository extends ReactiveCrudRepository<User, Long> {

    Mono<User> findByUserGuid(UUID userGuid);
}

userRepository
                .findByUserGuid(userGuid)
                .switchIfEmpty(userRepository.save(new User(userGuid)))
                .block()

[mp911de]

Calling .block() does exactly that to the thread that the code is being called on: It blocks.

In my service I have one use cases when synchronous call to database is required

This is a perfectly valid application, however, you should pass in a Duration to ensure proper timeout handling. And, this is more important, please make sure that the Thread, that calls .block() isn't one from a non-blocking thread pool/event loop, otherwise you will prevent your entire application from progressing.