Proper way to chain multiple related db ( repository calls )

Question

Using Spring WebFlux and ReactiveCrudRepository

Assume we have

UserRepository, UserDetailsRepository, UserTransactionRepository

I want to find the user, find their details and their transaction and return a single DTO object. Separate calls would look lik

userRepo.findById
userDetailsRepo.findByUserId
userTransactionRepo.findByUserId

How id properly chain them?

userRepo.findById()
.map( u -> userDetails.findByUserId( u ))
.map( ud -> userTrans.findByUserId( u))
.map( data -> process....);

?

Answer 1

In ReactiveCrudRepository, the findById method returns Mono from the emitted entity. You must use flatMap().

return userRepo.findById(id)
                .switchIfEmpty(Mono.error(new UserNotFoundException("User not found")))
                 .zipWhen(u -> userDetails.findById(u))
                  .zipWhen(ud -> userTrans.findById(ud))
                   .map(tuple -> mapper(tuple.getT1().getT1(), tuple.getT1().getT2(), tuple.getT2()));

https://docs.spring.io/spring-data/commons/docs/current/api/org/springframework/data/repository/reactive/ReactiveCrudRepository.html