Is there a good way to have the client emit a `sea...

# apollo-kotlin

[Nick]

Is there a good way to have the client emit a sealed class for the response? I’d like to emit various states such as loading, failure, and success but I don’t want to have to implement this on every call, I’d rather just do it in one spot 😄

[mbonnin]

The main thing to be aware of is that in GraphQL, it is possible to have partial responses. So it's possible to have both errors and data

[mbonnin]

If you don't want to handle partial errors, it's perfectly fine to map all partial responses as errors

[mbonnin]

Then you can emit loading/failure/success from an Rx Observable or a coroutines Flow

[Nick]

ahhh, ok, thanks! I’m thinking something like this? What do you think?

sealed class Response<out T> {
    object Loading : Response<Nothing>()
    data class Failure(
        val message: String,
        val errors: List<Error>? = null,
        val cause: Throwable? = null
    ) : Response<Nothing>()

    data class Complete<out T>(
        val value: T?,
        val errors: List<com.apollographql.apollo.api.Error>? = null
    ) : Response<T>()
}

fun <D : Operation.Data, T : Any, V : Operation.Variables> ApolloClient.stateful(
    query: Query<D, T, V>,
    retries: Long = 1,
    fetchType: ResponseFetcher = ApolloResponseFetchers.NETWORK_FIRST
): Flow<Response<T>> {
    return query(
        query
    )
        .toBuilder()
        .responseFetcher(fetchType)
        .build()
        .watcher()
        .toFlow()
        .retry(retries)
        .map {
            Response.Complete(it.data, it.errors)
        }
        .onStart {
            emit(Response.Loading)
        }
}

I’m having an issue with the onStart and catch since the I’m mapping to a Complete , it’s expecting that all types emitted to be Complete Any suggestions?

[Nick]

meh, close enough:

fun <D : Operation.Data, T : Any, V : Operation.Variables> ApolloClient.stateful(
    query: Query<D, T, V>,
    fetchType: ResponseFetcher = ApolloResponseFetchers.NETWORK_FIRST
) = flow{
    try {
        emit(Response.Loading)
        val response = query(query).toBuilder().responseFetcher(fetchType).build().await()
        emit(Response.Complete(response.data, response.errors))
    } catch (ex: Exception) {
        emit(Response.Failure("Error executing $query", cause = ex))
    }
}

[mbonnin]

This looks promising. Is this not working?

[Nick]

i haven’t ran it yet 🙂