java-dataloader-guice

Overview

This library aims to reduce the friction of using java-dataloader in Guice-based projects, especially when combined with graphql-java.

Without java-dataloader-guice

Without java-dataloader-guice, you need to manually bind each DataLoader and use all of them to construct a DataLoaderRegistry. For example, each DataLoader would normally need a separate Guice binding such as:

@Provides
@RequestScoped
@Named("greeting")
public DataLoader<String, String> provideGreetingDataLoader(GreetingBatchLoader greetingBatchLoader) {
  return DataLoader.newDataLoader(greetingBatchLoader);
}

When dealing with lots of such bindings, it is easy to accidentally inject the wrong BatchLoader.

Next, you would then need to inject all of these DataLoaders to build the DataLoaderRegistry, for example:

@Provides
@RequestScoped
public DataLoaderRegistry provideDataLoaderRegistry(
    @Named("greeting") DataLoader<String, String> greetingDataLoader,
    @Named("farewell") DataLoader<String, String> farewellDataLoader,
    @Named("congratulations") DataLoader<String, String> congratulationsDataLoader
) {
  DataLoaderRegistry registry = new DataLoaderRegistry();
  registry.register("greeting", greetingDataLoader);
  registry.register("farewell", farewellDataLoader);
  registry.register("congratulations", congratulationsDataLoader);

  return registry;
}

Keeping all the generic signatures and names in order is tedious and error-prone. And when adding a new DataLoader, it is easy to forget to add it to the registry.

In addition, when used with graphql-java, resolvers are normally singletons which creates an impedance mismatch with request-scoped DataLoader instances. This means carefully injecting Providers where needed to avoid OutOfScopeExceptions, for example:

private final Provider<DataLoader<String, String>> greetingDataLoader;
private final Provider<DataLoader<String, String>> farewellDataLoader;
private final Provider<DataLoader<String, String>> congratulationsDataLoader;

@Inject
public SalutationResolver(
    @Named("greeting") Provider<DataLoader<String, String>> greetingDataLoader,
    @Named("farewell") Provider<DataLoader<String, String>> farewellDataLoader,
    @Named("congratulations") Provider<DataLoader<String, String>> congratulationsDataLoader
) {
  this.greetingDataLoader = greetingDataLoader;
  this.farewellDataLoader = farewellDataLoader;
  this.congratulationsDataLoader = congratulationsDataLoader;
}

With java-dataloader-guice

With java-dataloader-guice, it only takes one line of code to bind each DataLoader, for example:

DataLoaderBinder.newDataLoaderBinder(binder)
    .bindDataLoader("greeting").toBatchLoader(GreetingBatchLoader.class)
    .bindDataLoader("farewell").toBatchLoader(FarewellBatchLoader.class)
    .bindDataLoader("congratulations").toBatchLoader(CongratulationsBatchLoader.class);

This will create the appropriate DataLoader bindings and also add them to a MapBinder. This MapBinder is used by DataLoaderModule to automatically bind a DataLoaderRegistry that will always include all your DataLoaders. In addition, the DataLoaders are bound as singletons and handle the request-scoping internally, which means that they don't need to be wrapped in a Provider when injected into graphql-java resolvers.

Usage

Maven dependency

<dependency>
  <groupId>com.hubspot.dataloader</groupId>
  <artifactId>java-dataloader-guice</artifactId>
  <version>0.1</version>
</dependency

Binding

Install the DataLoaderModule, this handles binding a request-scoped DataLoaderRegistry:

binder.install(new DataLoaderModule());

Bind all your BatchLoader/MappedBatchLoader:

DataLoaderBinder.newDataLoaderBinder(binder)
    .bindDataLoader("greeting").toBatchLoader(GreetingBatchLoader.class)
    .bindDataLoader("farewell").toMappedBatchLoader(FarewellBatchLoader.class);

For a full usage example, see this test