Batching resolvers (data fetchers)

[jugalthakkar]

I really like the way that graphql-java-tools minimised boilerplate code and helped in getting started very quickly.
I am at a stage where I want to optimise my code for performance and came across batching in graphql-java. This seems to be what I am looking for, but unable to find example to do this in graphql-java-tools.

Is there a documented way of achieving this? Or an example of how we can mix and use both graphql-java-tools and graphql-java together as per requirement?

[oliemansm]

Are you using just graphql-java-tools or are you using it in combination with graphql-spring-boot-starter? There's an example on how to use data loaders in that repo, see: https://github.com/graphql-java-kickstart/graphql-spring-boot/tree/master/example-request-scoped-dataloader.

[vojtapol]

What you are talking about is not really batching (the batch strategy is deprecated) but data loading. That concept is unrelated to this library. Data loaders are usually accessible via DataFetchingEnvironment which is a graphql-java class and you can access an instance of it in each of your graphql-java-tools resolvers.

[benmccann]

I had the same question while trying to get this setup with Micronaut. When you read the GraphQL Java docs they have a whole chapter on "batching" and make it sound very important that you implement a BatchLoader for each type. When using graphql-java-tools it looks like we use GraphQLResolver instead of DataFetcher and so there's this big open question in the docs of do we use BatchLoader or does graphql-java-tools have its own version of that too? If we do use BatchLoader how to we integrate it since some of the APIs are different (e.g. now we use SchemaParser, SchemaParserBuilder, etc. instead of the graphql-java versions)

It looks like several others have had this question as well: #370 #291 #290 #151 #58. There's a lot of different parts to put together a working GraphQL server and it's a bit tricky to figure out what to use from each library. Perhaps we could add something to the docs?

It looks like #58 has the best discussion of how this works

[benmccann]

I just got this working after much struggling. The key point I was missing is that your GraphQLResolver has to explicitly call the DataLoader. This wasn't very clear to me. Most of the examples that are available are for Spring and don't use graphql-java-tools, so don't have any examples that use a GraphQLResolver. It's also a little confusing because eventhough it's a BatchLoader, you're only calling it with a single key

[benmccann]

Now that I know how things work, https://github.com/graphql-java-kickstart/samples/tree/master/tools-hello-world doesn't seem very realistic. Everytime you get a character from the repository all their friends are returned too. But that's not really how you'd actually set things up if your app is backed by an RDBMS, which is the common case, because it'd be wasteful to fetch the friends if the GraphQL query doesn't request them. Instead, I think this would be the perfect place to demonstrate the usage of a BatchLoader.

[vojtapol]

Glad you figured it out. I took me a while too as you can see in #58.

The example you linked is correct. It might not be very realistic but it keeps things simple. Maybe we should add a separate example that demonstrates the use of data loader. There will always be a little bit of overfetching or underfetching when you back the GraphQL API with an RDBMS.

[mxmlnglt]

Now that I know how things work, https://github.com/graphql-java-kickstart/samples/tree/master/tools-hello-world doesn't seem very realistic. Everytime you get a character from the repository all their friends are returned too. But that's not really how you'd actually set things up if your app is backed by an RDBMS, which is the common case, because it'd be wasteful to fetch the friends if the GraphQL query doesn't request them.

Hello @benmccann, regarding the example you're referring to: what do you mean by all their friends are returned too?

Is that what's done in the methods in the QueryResolver?
https://github.com/graphql-java-kickstart/samples/blob/master/tools-hello-world/src/main/java/hello/resolvers/Query.java

e.g. for a single search (by id), retrieving the whole data?

  public Character character(String id) {
    return characterRepository.getCharacters().get(id);
  }

[benmccann]

See here: https://github.com/graphql-java-kickstart/samples/blob/5a75ad6e025b06d35abf9a66d558fef3d81c7df9/tools-hello-world/src/main/java/hello/CharacterRepository.java#L37