Apollo Federation for Hot Chocolate

This is a fork of HotChocolate.Federation module that aims to provide first class Apollo Federation support for HotChocolate subgraphs.

Apollo Federation is a powerful, open architecture that helps you create a unified supergraph that combines multiple GraphQL APIs. ApolloGraphQL.Federation.HotChocolate provides Apollo Federation support for building subgraphs in the HotChocolate ecosystem. Individual subgraphs can be run independently of each other but can also specify relationships to the other subgraphs by using Federated directives. See Apollo Federation documentation for details.

graph BT;
  router([Supergraph<br/>router]);
  serviceA[Users<br/>subgraph];
  serviceB[Products<br/>subgraph];
  serviceC[Reviews<br/>subgraph];
  router --- serviceA & serviceB & serviceC;

Installation

ApolloGraphQL.Federation.HotChocolate package is published to Nuget. Update your .csproj file with following package references

  <ItemGroup>
    <!-- make sure to also include HotChocolate package -->
    <PackageReference Include="HotChocolate.AspNetCore" Version="13.5.1" />
    <!-- federation package -->
    <PackageInstallation packageName="ApolloGraphQL.Federation.HotChocolate"/>
  </ItemGroup>

After installing the necessary packages, you need to register Apollo Federation with your GraphQL service.

var builder = WebApplication.CreateBuilder(args);

builder.Services
    .AddGraphQLServer()
    .AddApolloFederation()
    // register your types and services
    ;

var app = builder.Build();
app.MapGraphQL();
app.Run();

Usage

Refer to HotChocolate documentation for detailed information on how to create GraphQL schemas and configure your server.

Apollo Federation requires subgraphs to provide some additional metadata to make them supergraph aware. Entities are GraphQL objects that can be uniquely identified across the supergraph by the specified @keys. Since entities can be extended by various subgraphs, we need an extra entry point to access the entities, i.e. subgraphs need to implement reference resolvers for entities that they support.

Currently ApolloGraphQL.Federation.HotChocolate supports only Apollo Federation v1. See Apollo documentation for additional Federation details.

Annotation

All federated directives are provided as attributes that can be applied directly on classes/fields/methods.

[Key("id")]
public class Product
{
    public Product(string id, string name, string? description)
    {
        Id = id;
        Name = name;
        Description = description;
    }

    [ID]
    public string Id { get; }

    public string Name { get; }

    public string? Description { get; }

    // assumes ProductRepository with GetById method exists
    // reference resolver method must be public static
    [ReferenceResolver]
    public static Product GetByIdAsync(
        string id,
        ProductRepository productRepository)
        => productRepository.GetById(id);
}

This will generate following type

type Product @key(fields: "id") {
    id: ID!
    name: String!
    description: String
}

Federation Attributes

Directives

• Key applicable on objects, see @key documentation
• ExtendService applicable on objects, see @extends documentation
• External applicable on fields, see @external documentation
• Provides applicable on fields, see @provides documentation
• Requires applicable on fields, see @requires documentation

Entity resolution

• Map applicable on entity resolver method paramaters, allows you to map complex argument to a simpler representation value, e.g. [Map("foo.bar")] string bar
• ReferenceResolver applicable on static public methods to indicate entity resolver

Code First

Alternatively, if you need more granular control, you can use code first approach and manually populate federation information on the underlying GraphQL type descriptor. All federated directives expose corresponding methods on the applicable descriptor.

public class Product
{
    public Product(string id, string name, string? description)
    {
        Id = id;
        Name = name;
        Description = description;
    }

    [ID]
    public string Id { get; }

    public string Name { get; }

    public string? Description { get; }
}

public class ProductType : ObjectType<Product>
{
    protected override void Configure(IObjectTypeDescriptor<Product> descriptor)
    {
        descriptor
            .Key("id")
            .ResolveReferenceWith(t => GetProduct(default!, default!));
    }

    private static Product GetProduct(
        string id,
        ProductRepository productRepository)
        => productRepository.GetById(upc);
}

This will generate following type

type Product @key(fields: "id") {
    id: ID!
    name: String!
    description: String
}

Contact

If you have a specific question about the library or code, please start a discussion in the Apollo community forums or start a conversation on our Discord server.

Contributing

To get started, please fork the repo and checkout a new branch. You can then build the library locally by running

# install dependencies
dotnet restore
# build project
dotnet build
# run tests
dotnet test

See more info in CONTRIBUTING.md.

After you have your local branch set up, take a look at our open issues to see where you can contribute.

Security

For more info on how to contact the team for security issues, see our Security Policy.

License

This library is licensed under The MIT License (MIT).