Hi everyone! I am currently working on implementing custom error handling and logging using GraphQl ...

# graphql-kotlin

[Hector Gonzalez]

Hi everyone! I am currently working on implementing custom error handling and logging using GraphQl and Kotlin on a federated service. Does anyone have a current example on how to do this? The examples I've found online seem to use deprecated classes.

[Dariusz Kuc]

which library are you using? if you are using graphql-kotlin or graphql-java it should be the same as in non-federated service
• for error handling you probably want to specify your own DataFetcherExceptionHandler
• for logging (if it is something that you want to configure globally) you could use instrumentation

[Hector Gonzalez]

Hi Dariusz and thanks for the response. We are using graphql-kotlin I've tried implementing `DataFetcherExceptionHandler`without success.

[Hector Gonzalez]

On the application properties I've set: exception-handlers-enabled: true

I've also created a class to handle exceptions like this:

[Hector Gonzalez]

@Component
class CustomGraphQlErrorHandler: DataFetcherExceptionHandler {
    private val logger = LoggerFactory.getLogger(CustomGraphQlErrorHandler::class.java)

    @ExceptionHandler
    override fun onException(handlerParameters: DataFetcherExceptionHandlerParameters?): DataFetcherExceptionHandlerResult {
        val exception= handlerParameters?.exception
        val sourceLocation= handlerParameters?.sourceLocation
        val path= handlerParameters?.path

        val error = ExceptionWhileDataFetching(path, exception, sourceLocation)

        return DataFetcherExceptionHandlerResult.newResult().error(error).build()
    }
}

[Dariusz Kuc]

unsure what is the exception-handlers-enabled property as it is not something we use within the library

[Dariusz Kuc]

as for the error handler it looks correct (https://github.com/ExpediaGroup/graphql-kotlin/blob/master/graphql-kotlin-spring-server/src/main/kotlin/com/expediagroup/graphql/spring/exception/KotlinDataFetcherExceptionHandler.kt)

[Dariusz Kuc]

are you using graphql-kotlin-spring-server?

[Hector Gonzalez]

yes, we are using graphql-kotlin-spring-server
I'm not sure if the way I'm trying to trigger that code may be wrong though.
What I'm currently doing is trying to retrieve a non-existing field in our schema. And that does triggers a validation error, but the code in the handler doesn't seem to execute.

[Hector Gonzalez]

If I throw an Exception in the resolver then the onHandle method executes just fine, but in cases where schema validation fails, it's not executed. Particularly we want to be able to change the message contents in errors like this:

[Hector Gonzalez]

{
  "errors": [
    {
      "message": "Validation error of type FieldUndefined: Field 'categoryNames' in type 'Category' is undefined @ 'getCategoryById/categoryNames'",
      "locations": [
        {
          "line": 4,
          "column": 5
        }
      ]
    }
  ]
}

[Dariusz Kuc]

query validation happens before any of the exception handlers

[Dariusz Kuc]

unsure if there is a way to customize those validation messages

[Dariusz Kuc]

we are relying on graphql-java logic there so you can take a look at their documentation but I don’t recall any way to customize validation exception handling

[Hector Gonzalez]

I'll take a look at their documentation then. Thank you so much Dariusz!