Hi, I have a question regarding Spring graphQL data/error management. I have a use case where I want...

# server

[Pablo Schmid]

Hi, I have a question regarding Spring graphQL data/error management.
I have a use case where I want to return several results, including the error ones, as a Union.
something like this:

extend type Mutation {
userCreate(): UserCreatePayload
}
union UserCreatePayload = UserCreated | UserAlreadyExists

I have a MutationsResolver that handles the userCreate mutation by calling a UserService that is transactional.
When trying to create a user, if the user already exists, I'm throwing a UserAlreadyExist Exception that is handled in the mutation resolver with a try/catch block and then mapped to the UserAlreadyExists type in graphql.
The problem is that as the UserService is transactional, whenever I throw the exception, the transaction is marked a rollbackOnly by spring (which is good) and then the graphql flow goes through the DefaultGraphQLErrorHandler that finally return an error to the end user.
I would like to have the exactly same behavior except for the graphql error handler returning a GraphqlError. Instead I want to return the UserAlreadyExists type I defined in the graphql schema.
Is there anyway to do so? (I do not want to use sealed classes instead of exceptions in the service as the code gets dirty)
Thanks!

[Dariusz Kuc]

which GraphQL server implementation are you using?

[Pablo Schmid]

graphql-java

[Dariusz Kuc]

graphql-java is a GraphQL implementation but doesn't define a server (as that is a higher level concept) -> some libs built on top of graphql-java providing server functionality
• graphql-kotlin (I'm one of the maintainers of it)
• graphql-java-kickstart
• netflix-dgs
• spring-graphql

[Dariusz Kuc]

*or your own altogether

[Dariusz Kuc]

depending on the server they might be some differences in how you define your resolvers

[Pablo Schmid]

yes. graphql-java-kickstart is the one I'm using.

[Dariusz Kuc]

I'd assume you could just return the UserAlreadyExist from your try/catch block in the reesolver?

[Dariusz Kuc]

i.e. instead of throwing an exception from a resolver just return an object?

[Pablo Schmid]

I'm doing that. The problem is that as spring marked the transaction as rollbackOnly, then the flow goes through the DefaultGraphQLErrorHandler and the end user is getting the graphql error instead of the data

[Dariusz Kuc]

sounds like its caused by Spring and not really graphql-java-kickstart

[Dariusz Kuc]

you probably can create custom exception handler but that would require some custom logic

[Dariusz Kuc]

i.e. something along the lines https://github.com/ExpediaGroup/graphql-kotlin/blob/master/examples/server/spring-[…]s/server/spring/exceptions/CustomDataFetcherExceptionHandler.kt

[Pablo Schmid]

That might help. Thank you. I will let you know if it worked.

[Pablo Schmid]

Unfortunately this did not work as the return type of the onException function is a DataFetcherExceptionHandlerResult and not a DataFetcherResult

[Pablo Schmid]

I ended up adding the noRollbackFor = [MyException.class] to the Transactional annotation. By I'm not sure this is the safer approach.

[Pablo Schmid]

@Dariusz Kuc Finally I found the issue. My MutationResolver class had a @transactional which is conceptually wrong as it is a port adapter. By removing that @transactional everything worked as expected. There is no need to use the noRollbackFor .Many Regards.