在 HotChocolate 中拼接远程 GraphQL 模式时，`StringOperationFilterInput` 已被另一种类型注册

Question

I have a main GraphQL project which serves Books, and a secondary project which serves Movies, both including filtering. I'd like to add the secondary server's schema to the main one, so I can query for Movies on it by forwarding the query to the secondary. I used the Schema Stitching tutorial .

Without filtering it works well (I can hop onto /graphql on the main server and query for Movies), but adding [UseFiltering] to GetMovie generates an error:

The name `StringOperationFilterInput` was already registered by another type. (HotChocolate.Data.Filters.StringOperationFilterInputType)

   at HotChocolate.Configuration.TypeRegistry.Register(NameString typeName, RegisteredType registeredType)

Clearly both schemas generate types for filtering such as StringOperationFilterInput , but schema stitching doesn't want to merge them. Not sure what I can do here.

Minimal example: main project Program.cs :

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddHttpClient("Movies", c => c.BaseAddress = new Uri("https://localhost:7001/graphql"));
builder.Services.AddGraphQLServer()
    .AddQueryType<Query>()
    .AddRemoteSchema("Movies", ignoreRootTypes: true)
    .AddTypeExtensionsFromFile("./Stitching.graphql")
    .AddFiltering();

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

public record Book(string Name);

public class Query
{
    [UseFiltering] public IEnumerable<Book> GetBook() => new[] { new Book("A book") };
}

Main project's Stitching.graphql :

extend type Query {
  movies: [Movie!]! @delegate(schema: "Movies", path:"movie")
}

Secondary project Program.cs :

var builder = WebApplication.CreateBuilder(args);

builder.WebHost.UseUrls("https://localhost:7001/");
builder.Services.AddGraphQLServer()
    .AddQueryType<Query>()
    .AddFiltering();

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

public record Movie(string Name);

public class Query
{
    [UseFiltering] public IEnumerable<Movie> GetMovie() => new[] { new Movie("Die Hard") };
}

Answer 1

I figured it out. First of all, we need to add a TypeMergeHandler that skips remote types which are already registered. Unfortunately, the duplicated types to skip have to be hardcoded, since there's no apparent way to inspect already-registered types. I kept adding reported duplicated types based on error messages GraphQL printed.

builder.Services.AddTypeMergeHandler<GraphqlTypeMergeHandler>()

public class GraphqlTypeMergeHandler : ITypeMergeHandler
{
    private readonly MergeTypeRuleDelegate _next;

    private readonly string[] _duplicateTypes = new[]
    {
        "ComparableNullableOfDateTimeOperationFilterInput",
        "ComparableNullableOfDecimalOperationFilterInput",
        "ComparableNullableOfInt32OperationFilterInput",
        "BooleanOperationFilterInput",
        "StringOperationFilterInput",
        "SortEnumType",
        "PageInfo",
    };

    public GraphqlTypeMergeHandler(MergeTypeRuleDelegate next) => _next = next;

    public void Merge(ISchemaMergeContext context, IReadOnlyList<ITypeInfo> types)
    {
        var typeName = types[0].Definition.Name.Value;

        if (_duplicateTypes.Contains(typeName))
            return;

        _next(context, types);
    }
}

Secondly, Stitching.graphql needs to be adjusted for filtering support, since the Movie query now includes the where parameter:

extend type Query {
    movies(where: MovieFilterInput): [Movie!]!
    @delegate(schema: "Movies", path:"movie(where: $arguments:where)")
}

And lastly, the Book and Movie types in my example are records with positional syntax, while GraphQL types must have a parameterless constructor.