Types marked with @key directive are not getting resolved, the fields are getting resolved as null

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,
1

As part of our apollo federation, we have 3 subgraphs.
content
bookmarking
coral
In the content subgraph, we have marked around 5 entities with the @key directive and all of these entities are resolved within the content subgraph, which is extended in bookmarking. If I am querying only content subgraph using any graphql client, I am able to receive the response. but if I am querying my bookmarking service which internally resolves to my content subgraph through apollo gateway. I am able to see the fields are getting resolved to null.

Sample Code Snippet Below:

The entity of the content subgraph:

type Recipe implements IRecipe & Node & Content & HasContributors & HasMedia & HasRecommendations & HasSEO & Publishable & Recommendable @key(fields: "id organizationId"){
 """ID of the Recipe"""
  id: ID!

""ID of the Organization associated with the Recipe""
  organizationId: ID!
"""Headline of the Recipe"""
hed(textFormat: TEXT_FORMAT = MARKDOWN): String
.....
}

Extended in bookmarking subgraph:

type Bookmark @cacheControl(maxAge: 300) {
    id: Int!
    organizationId: String
    copilotId: String
    siteCode: String
    documentUrl: String
    bookmarkName: String
    documentType: String
    meta: String
    amgUUID: String!
    collections(limit: Int!, offset: Int!): [Bookmarkcollection!]!
    totalCollectionCount:Int
    content: DocumentType
  }

union DocumentType = Article | Photo | Gallery | Recipe | NativeRecipe
extend type Recipe @key(fields: "id organizationId") {
    id: ID! @external
    organizationId: ID! @external
    isBookmarked(amgUUID: ID!): Boolean
  }

Query:

query{
 bookmark(id: 547) {
   amgUUID
   content{
     ... on Recipe{
       hed
     }
   }
 }
}

Response:

{
  "data": {
    "bookmark": {
      "amgUUID": "b44449da-bae2-4160-abc8-2fdaee4ad37d",
      "content": {
        "hed": null
      }
    }
  }
}

Except for the @key directive fields id and organizationId, the above query is not resolving other fields in the recipe content subgraph.
The field resolves if I am querying only the content subgraph.

apollo-server-koa: "2.21.1",
@graphql-tools/merge: "8.2.7",
@graphql-tools/schema: "8.5.0",
@graphql-tools/utils: "8.6.6",
graphql: "15.8.0"
@apollo/subgraph: 0.4.2

I am using the following code to compose my schema in Apollo Server.

const contentDirectiveTypeDefs = getContentDirectiveTypeDefs();
  const contentSchemaTransforms = getContentDirectiveTransformers();
  const sharedDirectiveTypeDefs = getSharedDirectiveTypeDefs();
  const sharedSchemaTransforms = getSharedDirectiveTransformers();

  const typeDefs = mergeTypeDefs([
    ...contentSchemas,
    ...contentDirectiveTypeDefs,
    ...sharedDirectiveTypeDefs,
    Modules.schema,
  ]);

  const resolvers = mergeResolvers([contentResolvers, Modules.resolvers]);

  let schema = addResolversToSchema({
    inheritResolversFromInterfaces: true,
    resolvers,
    schema: buildSubgraphSchema([{ typeDefs }]),
  });

  const directives = Modules.schemaDirectives;
  SchemaDirectiveVisitor.visitSchemaDirectives(schema, directives);
  contentSchemaTransforms.forEach((transformedSchema) => {
    schema = transformedSchema(schema);
  });
  sharedSchemaTransforms.forEach((transformedSchema) => {
    schema = transformedSchema(schema);
  });

  const apolloServer = new ApolloServer({
    cache,
    schema,
    context: contextFunction,
    dataSources: (): DataSources =>
      dataSources({
        cneApiDataSourceOptions: {
          httpsAgent,
          cache: cneApi.cache,
          logger: createLogger(cneApi.log),
          cneApiUrl: cneApi.cneApiUrl,
        },
        contentApiDataSourceOptions: {
          httpsAgent,
          cache: contentApi.cache,
          logger: createLogger(contentApi.log),
        },
        ratingsApiDataSourceOptions: {
          cache: ratingsApi.cache,
          httpsAgent,
          logger: createLogger(ratingsApi.log),
        },
        recommendationsApiDataSourceOptions: {
          httpsAgent,
          recommendationsApiUrl: recommendationsApi.recommendationsApiUrl,
          logger: createLogger(recommendationsApi.log),
        },
        simpleRequestDataSourceOptions: {
          cache: simpleRequest.cache,
          httpsAgent,
          logger: createLogger(simpleRequest.log),
        },
        tsuguApiDataSourceOptions: {
          cache: tsuguApi.cache,
          logger: createLogger(tsuguApi.log),
          typesToResolve: tsuguApi.typesToResolve,
          tsuguInstances: tsuguApi.tsuguInstances,
        },
      }),
    validationRules: [depthLimit(queryDepthLimit)],
    extensions,
    debug: enableDebug,
    introspection: enableIntrospection,
    playground: {
      settings: {
        'schema.polling.enable': false,
      },
    } as PlaygroundConfig,
    plugins: [SchemaHashPlugin],
    tracing: enableTracing,
  });

  apolloServer.applyMiddleware({ app });

  return apolloServer;
}

Apollo Gateway Query Plan:

QueryPlan {
  Sequence {
    Fetch(service: "bookmarking-service") {
      {
        bookmark(id: 0) {
          amgUUID
          content {
            __typename
            ... on Recipe {
              __typename
              id
              organizationId
            }
          }
        }
      }
    },
    Flatten(path: "bookmark.content") {
      Fetch(service: "content") {
        {
          ... on Recipe {
            __typename
            id
            organizationId
          }
        } =>
        {
          ... on Recipe {
            hed
          }
        }
      },
    },
  },
}
2

I have resolved this issue, I had missed adding resolvers in my buildSubgrapSchema,
schema: buildSubgraphSchema([{ typeDefs }]) My initial understanding was addResolversToSchema method will attach the resolvers to my subgraph service but it looks like it’s not.