gqlgen: Apollo Federation: 422: Unprocessable Entity when no entity defined

What happened?

There is a service which only contains a mutation which has only input types defined:

extend type Mutation {
  addSurveyResult(result: SurveyResult!): ID
}

input SurveyResultTuple {
     key: String
     value: String
}

input SurveyResult {
  userId: ID!

  type: String!

  elements: [SurveyResultTuple!]!
}

when I try to federate the service by a gateway the following errors occure:

Service:

unknown field “_service”

goroutine 9 [running]: runtime/debug.Stack(0x1, 0x0, 0x0) /usr/local/go/src/runtime/debug/stack.go:24 +0x9d runtime/debug.PrintStack() /usr/local/go/src/runtime/debug/stack.go:16 +0x22 github.com/99designs/gqlgen/graphql.DefaultRecover(0xc0c740, 0xc0002c8690, 0x9fe620, 0xc0001b8de0, 0x44900f, 0x18) /home/simon/go/pkg/mod/github.com/99designs/gqlgen@v0.11.1/graphql/recovery.go:16 +0xa7 github.com/99designs/gqlgen/graphql/handler.(*Server).ServeHTTP.func1(0xc0000d5e40, 0xc00013fbd0, 0xc0ae40, 0xc0002922a0) /home/simon/go/pkg/mod/github.com/99designs/gqlgen@v0.11.1/graphql/handler/server.go:124 +0xa7 panic(0x9fe620, 0xc0001b8de0) /usr/local/go/src/runtime/panic.go:679 +0x1b2 recommender-survey-archive/cmd/graph/generated.(*executionContext)._Query(0xc0001b8da0, 0xc0c740, 0xc0002c8ff0, 0xc0001b8b40, 0x1, 0x1, 0x40dcc6, 0xc0002c8fc0) /home/simon/go/src/recommender-survey-archive/cmd/graph/generated/generated.go:1527 +0x6b4 recommender-survey-archive/cmd/graph/generated.(*executableSchema).Exec.func1(0xc0c740, 0xc0002c8fc0, 0x10) /home/simon/go/src/recommender-survey-archive/cmd/graph/generated/generated.go:99 +0x7b github.com/99designs/gqlgen/graphql/handler.executor.DispatchOperation.func1.1.1(0xc0c740, 0xc0002c8fc0, 0xc0001b8db0) /home/simon/go/pkg/mod/github.com/99designs/gqlgen@v0.11.1/graphql/handler/executor.go:100 +0x43 github.com/99designs/gqlgen/graphql/handler.newExecutor.func2(0xc0c740, 0xc0002c8fc0, 0xc0001b8db0, 0xbeec60) /home/simon/go/pkg/mod/github.com/99designs/gqlgen@v0.11.1/graphql/handler/executor.go:33 +0x3a github.com/99designs/gqlgen/graphql/handler.executor.DispatchOperation.func1.1(0xc0c740, 0xc0002c8f60, 0xc0002c8690) /home/simon/go/pkg/mod/github.com/99designs/gqlgen@v0.11.1/graphql/handler/executor.go:99 +0x130 github.com/99designs/gqlgen/graphql/handler/transport.POST.Do(0xc0ae40, 0xc0002922a0, 0xc00028e300, 0xc0b300, 0xc0000c0ff0) /home/simon/go/pkg/mod/github.com/99designs/gqlgen@v0.11.1/graphql/handler/transport/http_post.go:52 +0x353 github.com/99designs/gqlgen/graphql/handler.(*Server).ServeHTTP(0xc0000d5e40, 0xc0ae40, 0xc0002922a0, 0xc00028e300) /home/simon/go/pkg/mod/github.com/99designs/gqlgen@v0.11.1/graphql/handler/server.go:140 +0x23c net/http.(*ServeMux).ServeHTTP(0x106d9c0, 0xc0ae40, 0xc0002922a0, 0xc00028e200) /usr/local/go/src/net/http/server.go:2387 +0x1bd net/http.serverHandler.ServeHTTP(0xc0002921c0, 0xc0ae40, 0xc0002922a0, 0xc00028e200) /usr/local/go/src/net/http/server.go:2802 +0xa4 net/http.(*conn).serve(0xc000270b40, 0xc0c680, 0xc000290b00) /usr/local/go/src/net/http/server.go:1890 +0x875 created by net/http.(*Server).Serve /usr/local/go/src/net/http/server.go:2928 +0x384

Gateway:

Encountered error when loading recommender-survey-archive at http://localhost:4004/query: 422: Unprocessable Entity

When the following graphql type is added everything works smoothly

type Workaround @key(fields: "id") {
  id: Int
}

Note: @key is required for this workaround

What did you expect?

I don’t understand the details but I would expect gqlgen to add the following Query without the Workaround type, so that the service can be federated:

extend type Query {
   _entities(representations: [_Any!]!): [_Entity]!
   _service: _Service!
}

Minimal graphql.schema and models to reproduce

See above.

versions

• gqlgen version?

v0.11.1

• go version?

go version go1.13.6 linux/amd64

EDIT: Btw. I want to thank you for providing a go lib that allows to federate with apollo. You have created a really smooth technology that helps me a lot, great job and thank you!