Need help with regards to fallback of Uni via GraphQL interface

[sandip-stats]

Hi

Context -
Using quarkus-smallrye-graphql, quarkus-hibernate-reactive-panache, quarkus-hibernate-reactive-panache.
Flow --> Call the Graphql resource, Get data from Postgres (in the form of Uni), Cache the data (Used CachedResult) and return it (in the form of Uni).
This works perfectly fine.

The Code Snippet looks like:

@Query(value = "issuerDetails")
public Uni<IssuerData> getBankDetails(@Name("issuerid") Integer issuerid) {
      Uni<IssuerData> issuerInformationFrmDB = db.getIssuerLevelDetails(bankId);
      return issuerInformationFrmDB.onFailure().transform(ex -> {
			return exceptionHandler.customException(gQLContext.getArguments().toString(), ex);
       });
}

Q's
However am not able to figure out a variant OR how to achieve it, where-in i want to call a different service (which returns a Uni) AND only if the call does not return anything (could have timed-out or returned NULL) make a DB call.

The Code snippet i tried looks like:

@Query(value = "issuerDetails")
public Uni<IssuerData> getBankDetails(@Name("issuerid") Integer issuerid) {
      Uni<IssuerData> issuerInformationFrmServiceA = serviceA.getIssuerLevelDetails(bankId);
      Uni<IssuerData> issuerInformationFrmDB = db.getIssuerLevelDetails(bankId);
      return issuerInformationFrmServiceA.onItem().ifNull().switchTo(issuerInformationFrmDB);
}

The above code is returning null always :(

Any help/suggestion would be appreciated.

[jponge]

If it times out it's likely that you get a failure, so onFailure() is what you might have better luck with.

BTW you can use .log() to see all events that go through a given operator, it's a very useful tool.

[sandip-stats]

Thanks @jponge. Tried with both a Failure (onFailure) scenario and a NULL (as is in the above code) and both work.
For Failure case, used:
return issuerInformationFrmServiceA.onFailure().recoverWithUni(issuerInformationFrmDB)
For NULL case, the above code worked
The reason the above code was not working was cause the issuerInformationFrmServiceA was not returning null (mocked the serviceA.getIssuerLevelDetails(bankId) with return Uni.createFrom().nullItem()) and all seems to be working.

I did try using the log() but was not very clear on its output (unless of course am using it incorrectly); i.e :
return issuerInformationFrmServiceA.onItem().ifNull().switchTo(issuerInformationFrmDB).log();
yielded

2022-12-07 19:47:42,036 INFO  [io.qua.mut.run.MutinyInfrastructure] (vert.x-eventloop-thread-0) Uni.UniOnItemTransformToUni.0 | onSubscribe()
2022-12-07 19:47:42,234 INFO  [io.qua.mut.run.MutinyInfrastructure] (vert.x-eventloop-thread-0) Uni.UniOnItemTransformToUni.0 | onItem(com.arcot.issuerconfiguration.data.BankData@2db4d3ac)

This is not giving out the information that we switched cause the item is null.