Add example of using DataLoader

[benmccann]

Thank you so much for providing this project! I'm trying to set my project up following the todo-java-tools example. I noticed that example and none of the others demonstrate using a DataLoader and I'm having a hard time figuring it out. (I do see some support was added). I'd love it if this were something that could be added to the example

Thanks again!

[marceloverdijk]

Hi @benmccann thx for reaching out!

The todo-java-tools is not suited for a DataLoader as it is not retrieving any other data.

The DataLoader pattern is suited if for example a ToDo would have a Owner (Person) which would need to be queried from a database or retrieved from another webservice.

It should be setup like:

@Factory
public class DataLoaderRegistryFactory {

    private static final Logger LOG = LoggerFactory.getLogger(DataLoaderRegistryFactory.class);

    private final PersonBatchLoader personBatchLoader;

    public DataLoaderRegistryFactory(PersonBatchLoader personBatchLoader) {
        this.personBatchLoader = personBatchLoader;
    }

    @RequestScope
    public DataLoaderRegistry dataLoaderRegistry() {
        var dataLoaderRegistry = new DataLoaderRegistry();
        dataLoaderRegistry.register("person", DataLoader.newDataLoader(personBatchLoader));
        LOG.trace("Created new data loader registry");
        return dataLoaderRegistry;
    }
}

Important is to have it @RequestScope'd so for every request the DataLoaders are re-created.

@Singleton
public class PersonBatchLoader implements BatchLoader<Long, Person> {

    private static final Logger LOG = LoggerFactory.getLogger(PersonBatchLoader.class);

    private final PersonRepository personRepository;
    private final ExecutorService executor;

    public PersonBatchLoader(PersonRepository personRepository,
            @Named(TaskExecutors.IO) ExecutorService executor) {
        this.personRepository = personRepository;
        this.executor = executor;
    }

    @Override
    public CompletionStage<List<Person>> load(List<Long> keys) {
        LOG.debug("Batch loading persons with keys: {}", keys);
        return CompletableFuture.supplyAsync(() -> keys
                .stream()
                .map(id -> personRepository.findById(id).orElse(null))
                .collect(Collectors.toList()), executor);
    }
}

and then in a DataFetcher:

@Singleton
public class ToDoOwnerDataFetcher implements DataFetcher<CompletionStage<Person>> {

    private static final Logger LOG = LoggerFactory.getLogger(ToDoOwnerDataFetcher.class);

    @Override
    public CompletionStage<Person> get(DataFetchingEnvironment environment) {
        ToDo toDo = environment.getSource();
        var ownerId = toDo.getOwnerId();
        if (ownerId == null) {
            return null;
        }
        LOG.debug("Fetching owner with id: {}", ownerId);
        DataLoader<Long, Person> personDataLoader = environment.getDataLoader("person");
        return personDataLoader.load(ownerId);
    }
}

But this is for a plain Java implementation, not using Java Tools.
I'm not familiar myself with Java Tools so I don't know if and how they support the DataLoader pattern.

Hope this helps.

[benmccann]

Nice! This is super helpful!!

Is the personDataLoader something that is automatically provided by micronaut-graphql?

Will the GraphQL execution engine sometimes call the data loader (e.g. when a join is occuring) or do I always need to manually invoke it from a DataFetcher?

I don't think Java Tools does anything special as far as data loaders go, so adding this to chat or any of the other examples would be just as equally helpful

Thanks again for all your help on this!

[marceloverdijk]

Hi @benmccann

I will update the ToDo examples to include a DataLoader example this week! Stay tuned.

[benmccann]

That would be fantastic! Thank you so much!!

[benmccann]

Hey @marceloverdijk I just thought I'd check in and see if you might still have a chance to update the example? Thanks again for all your help

[marceloverdijk]

Sorry @benmccann got delayed a bit but thx for the reminder. Will look at it soon!

[benmccann]

I figured out how to do this, so feel free to close

I do have one Micronaut-specific question though. There are a couple places in the setup where I need to inject everything of a certain type. E.g. inject an instance of every BatchLoader to register in DataLoaderRegistryFactory or inject an instance of every GraphQLQueryResolver to register in GraphQLFactory. This can be a little tedious and verbose. Is there a way to inject a List of every subclass of a certain type?

I saw someone mention they were doing this in Spring with:

@Autowired
public RegistryBuilder(List<BatchLoader> batchLoaders)

[marceloverdijk]

No pls keep it open. I just didn't find the time yet :-(

The pattern you are talking about I'm also seeing with DataFetcherss and indeed it is a bit tedious and verbose.
I actually don't know if Micronaut support List injections of a certain type - like Spring - but I assume so. I used that technique in the past in a Spring application as well, but honestly I don't kow which pattern I prefer :-)

[benmccann]

It turns out you can inject a List of all instances. I simplified my code below. Feel free to steal.

@Factory
@Slf4j
public class GraphQLFactory {

  @Singleton
  public GraphQL graphQL(List<GraphQLResolver<?>> resolvers) {

    log.debug("Registering " + resolvers.size() + " GraphQLResolvers");

    SchemaParserBuilder builder =
        SchemaParser.newParser().file("schema.graphql").resolvers(resolvers);

    // Create the executable schema.
    GraphQLSchema graphQLSchema = builder.build().makeExecutableSchema();

    // Return the GraphQL bean.
    return GraphQL.newGraphQL(graphQLSchema).build();
  }
}

@Factory
public class DataLoaderRegistryFactory {

  private final List<BatchLoader<?, ?>> batchLoaders;

  @Inject
  public DataLoaderRegistryFactory(List<BatchLoader<?, ?>> batchLoaders) {
    this.batchLoaders = batchLoaders;
  }

  /**
   * It seems a little inefficient to create every DataLoader for every request, but that's what the
   * API is. https://github.com/graphql-java/graphql-java/issues/1902
   */
  @RequestScope
  public DataLoaderRegistry dataLoaderRegistry() {
    DataLoaderRegistry dataLoaderRegistry = new DataLoaderRegistry();
    for (BatchLoader<?, ?> loader : batchLoaders) {
      dataLoaderRegistry.register(
          loader.getClass().getSimpleName(), DataLoader.newDataLoader(loader));
    }
    return dataLoaderRegistry;
  }
}