Hi everyone. I'm trying to do some schema stitchin...

# graphql

[Hector Gonzalez]

Hi everyone. I'm trying to do some schema stitching using Apollo Gateway; I am able to consume both remote schemas, I also have definitions for schema extensions and resolvers. Basically, I am trying to retrieve the school "object" for a student, by using the schoolId. The catch being that the Student schema and School schema are in separate services. Not sure what I'm missing. I am unable to "join" both types using the resolver. Can you kindly help me out? Here´s the code:
*const* VCDB_URI = '<http://localhost:4001/graphql>'
*const* PCDB_URI = '<http://localhost:4002/graphql>'

//Define schema extensions
`*const* typeDefs = ``
  extend type Student {
    schoolId: School
  }
``;`

*const* resolvers = {
  Student: {
      schoolId(parent, args, context, info) {
        return delegateToSchema({
          schema: typeDefs,
          operation: 'query',
          fieldName: 'getBySchoolId',
          args: {
            schoolId: parent.id,
          },
          context,
          info,
        });
      }
  }
}

//Define the gateway
*const* gateway = new ApolloGateway({
  serviceList: [
    { name: 'vcdb', url: VCDB_URI },
    { name: 'pcdb', url: PCDB_URI },
  ],
  extensions: typeDefs,
  resolvers: resolvers,
  debug: true
});

//Define the server
*const* server = new ApolloServer(
  { gateway, 
    subscriptions: false,
   });

//Start up the server
server.listen({
  port: 4000,
*}).then(({ url }) =>* {
  `*console.log(*:rocket:  *Server ready at ${url});*`
});

[mbonnin]

Hi 👋 Given this is a Kotlin slack, you might have more luck in the GraphQL community: https://graphql.org/community/

[mbonnin]

Or in the Apollo spectrum: https://spectrum.chat/apollo/apollo-federation?tab=posts

[Hector Gonzalez]

I'll check them out. Thank you.

[Dariusz Kuc]

yeah spectrum would get you the answer the fastest

[Dariusz Kuc]

that being said it looks like you are trying to do schema stitching -> there are number of tutorials available for it, e.g. see https://www.graphql-tools.com/docs/stitch-schema-extensions

[Dariusz Kuc]

you might want to consider moving towards Apollo Federation which removes the need for having this logic on the gateway and allows you to define your relationships programmatically within the underlying services

[Dariusz Kuc]

i.e. your schema that contains school resolvers would extend the student with additional school field

[Hector Gonzalez]

The services that contain the school and student entities are already federated, but they are separate services. I'm not sure how they would be able to resolve each others' type without having to be in the same service. Hence I decided to put that logic in the gateway itself, but that approach isn't working either. It's not showing any errors at startup either, it's just not doing the stitching.

[Dariusz Kuc]

see https://www.apollographql.com/docs/apollo-server/federation/introduction/

[Hector Gonzalez]

I forgot to mention we are exposing the federated services with a combination of spring boot and expedia groups's jars, using Kotlin as well.

[Hector Gonzalez]

Only the gateway is using node.js

[Dariusz Kuc]

if you are using graphql-kotlin then take a look at https://expediagroup.github.io/graphql-kotlin/docs/federated/apollo-federation

[Dariusz Kuc]

and also https://github.com/ExpediaGroup/graphql-kotlin/tree/master/examples/federation

[Hector Gonzalez]

yes, I think I can find what I need there. Thank you so much Dariusz!

[Dariusz Kuc]

also an FYI when we switched from stitching to apollo federation it resulted in pretty significant performance improvement in the gateway so besides keeping the gateway dumb it also made it faster

[Hector Gonzalez]

yes, we are trying to prevent overfetching, so this might be the best solution. I am taking a closer look at the extended schema example seen here: https://expediagroup.github.io/graphql-kotlin/docs/federated/federated-schemas

[Hector Gonzalez]

and in the Product definition it's using a method getReviewByProductId(id) , I assume this method is the resolver for the Review, correct? and it's all part of the same project and service? The problem we are facing is that we are trying to fetch from a different project and service, so I'm not sure how to wire that up, if at all possible.

[Dariusz Kuc]

federation tldr
• service A knows about Product and how to fetch it
• service B knows about Reviews and how to fetch it, it “knows” that Product type exists somewhere so it just adds new field to it to fetch reviews (as it subject matter expert on how to fetch reviews)

[Hector Gonzalez]

Hi Dariusz, sorry to bother again with this topic. I think I've figured most of it, but for some reason I am unable to fetch both values from my School Entity so I've added an @ExternalDirective annotation to schoolName. But when I do that, the gateway errors out with this message: This data graph is missing a valid configuration. [vcdb] School.schoolName -> is marked as @external but is not used by a @requires, @key, or @provides directive.

[Hector Gonzalez]

This is is a diagram of the code I am using:

[Hector Gonzalez]

When I remove the @ExternalDirective from schoolName in service B, the gateway starts fine and I can retrieve Student -> School -> schoolId
But for some reason Student -> School -> schoolName won't work

[Dariusz Kuc]

do you have a sample github project that shows this behavior?

[Dariusz Kuc]

basically i think in your example it should be reversed
• service A defines School and extends Student with additional school field
• service B defines Student

[Dariusz Kuc]

i.e. since service A is subject matter expert on School it should have all the logic related to fetching that data

[Hector Gonzalez]

Unfortunately nothing I can publish on github, but I will try with the approach you are mentioning. Thank you

[Hector Gonzalez]

Hello again Dariusz, I've tried the approach you mentioned yesterday, now I am getting the following error when querying the gateway:

[Hector Gonzalez]

Service A schema looks like this:

[Hector Gonzalez]

Service B schema looks like:

[Hector Gonzalez]

Any help you could provide is greatly appreciated

[Hector Gonzalez]

Hi @Dariusz Kuc, sorry to be such a bother but I'm still struggling with the scenario above. Any input you can provide will be valuable.

[Dariusz Kuc]

your schemas look correct so the issue might be with your entity resolver

[Hector Gonzalez]

I suppose you mean the resolver for School in the Student extension correct? For now I am using a hardcoded object, but without success:

@KeyDirective(fields = FieldSet("studentId"))
@ExtendsDirective
class Student(@ExternalDirective val studentId: Long,
              @GraphQLIgnore val schoolId: Long
){
    fun school(): School? = School(99,"Hardcoded")
}

[Dariusz Kuc]

i meant resolver for entities query -> e.g. https://expediagroup.github.io/graphql-kotlin/docs/federated/type-resolution#federated-type-resolver

[Hector Gonzalez]

I was indeed missing that resolver. I have created it like this:

@Component
class StudentResolver(private val schoolRepository: SchoolRepository) : FederatedTypeResolver<Student> {

    override suspend fun resolve(environment: DataFetchingEnvironment, representations: List<Map<String, Any>>): List<Student?> =
        representations.map {

        val studentId = it["studentId"]?.toString()?.toLongOrNull() ?: throw InvalidStudentIdException()
        val schoolId = it["schoolId"]?.toString()?.toLongOrNull() ?: throw InvalidSchoolIdException()

        val school = schoolRepository.findSchoolBySchoolId(schoolId)

        if(school!=null){
            Student(studentId, schoolId, school)
        } else {
            null
        }

    }

    class InvalidStudentIdException : RuntimeException()
    class InvalidSchoolIdException : RuntimeException()

}

And added the resolver to the federated type registry in the SpringBootApplication class:

@SpringBootApplication
class DemoApplication

@Bean
fun federatedTypeRegistry(studentResolver: StudentResolver): FederatedTypeRegistry =
    FederatedTypeRegistry(mapOf("Student" to studentResolver))

fun main(args: Array<String>) {
    runApplication<DemoApplication>(*args)
}

[Hector Gonzalez]

However the problem is still there. I've put a breakpoint inside the resolver but it never triggers. I've also made sure that the package for both the student and the resolver is declared in our application.yml

[Hector Gonzalez]

Not sure what else is missing.

[Hector Gonzalez]

I've also enabled debugging on the gateway and path traversal seems correct to me:

QueryPlan {
  Sequence {
    Fetch(service: "vcdb") {
      {
        getByStudentId(studentId: 1) {
          schoolId
          studentId
          studentName
          __typename
        }
      }
    },
    Flatten(path: "getByStudentId") {
      Fetch(service: "pcdb") {
        {
          ... on Student {
            __typename
            studentId
          }
        } =>
        {
          ... on Student {
            school {
              schoolName
            }
          }
        }
      },
    },
  },
}

[Dariusz Kuc]

shouldn’t your configuration be

@SpringBootApplication
class DemoApplication {
  @Bean
  fun federatedTypeRegistry(studentResolver: StudentResolver): FederatedTypeRegistry =
    FederatedTypeRegistry(mapOf("Student" to studentResolver))
}

i.e. @Bean definitions should be included inside configuration class and not top level functions

[Hector Gonzalez]

Gosh I can't believe I missed the braces' position! Yes it seems to be properly wired now. The breakpoints are working now. Thank you so much!

[Dariusz Kuc]

👍