buildFederatedSchema only accepts one type definition

Hi, using buildFederatedSchema with multiple typeDefs are not possible? When using apollo-server I can pass an Array of DocumentNode for the parameter typeDefs as seen here: https://www.apollographql.com/docs/apollo-server/api/apollo-server/#parameters however when I use buildFederatedSchema it no longer takes an array and only one type def as seen here: https://www.apollographql.com/docs/apollo-server/api/apollo-federation/#buildfederatedschema

Shouldn’t these be the same?

How would you construct the following with buildFederatedSchema:

const server = new ApolloServer({
  typeDefs: [
    createRateLimitTypeDef('burstRateLimit'),
    createRateLimitTypeDef('sustainedRateLimit'),
    typeDefs,
  ],
  resolvers,
  schemaDirectives: {
    burstRateLimit: createRateLimitDirective(),
    sustainedRateLimit: createRateLimitDirective(),
  },
})

Not possible to pass an array to typeDefs:

const schema = buildFederatedSchema([
  {
    typeDefs: gql(typeDefs),
    resolvers,
  },
])

[NFabrizio]

@drager I had the same issue, and the solution that worked for me was the following.

const sandwichType = gql`
  type Sandwich {
    id: ID!
    description: String
  }
`;
const breadType = gql`
  type Bread {
    id: ID!
    description: String
  }
`;
const queryType = gql`
  type Query {
    getSandwichById(id: ID!): Sandwich
    getBreadById(id: ID!): Bread
  }
`;
const schema = buildFederatedSchema({
  typeDefs: [sandwichType, breadType, queryType],
  resolvers
})

For me when passing typeDefs and resolvers that are themselves arrays, I had to pass buildFederatedSchema an object instead of an array.

@trevor-scheer if you or one of the maintainers can confirm that this usage is correct, I would be happy to open a PR to add an example of how to pass arrays to buildFederatedSchema for the documentation for Apollo Federation.

EDIT: I spoke too soon. The above implementation eliminates the errors, but the server does not actually work. I will keep working on this and post any solutions I find.

UPDATE: The above example does work if resolvers is an object. It does not work if resolvers is also an array. If resolvers is an array, the server will start without error, but the resolvers will return null. While the above example does work with the condition of resolvers being an object, after digging through the code, it seems that Federation wants consumers to use a slightly different format, which is shown below. @trevor-scheer would you or one of the maintainers confirm if the below example is the desired usage for an app with multiple type definitions?

const sandwichType = gql`
  type Sandwich {
    id: ID!
    description: String
  }
`;
const breadType = gql`
  type Bread {
    id: ID!
    description: String
  }
`;
const queryType = gql`
  type Query {
    getSandwichById(id: ID!): Sandwich
    getBreadById(id: ID!): Bread
  }
`;
const sandwichResolver = {
  Query: {
    getSandwichById: (_, { id }, { dataSources }) => dataSources.getSandwichById(id)
  }
};
const breadResolver = {
  Query: {
    getBreadById: (_, { id }, { dataSources }) => dataSources.getBreadById(id)
  }
};
const schema = buildFederatedSchema([
  {
    typeDefs: sandwichType,
    resolvers: sandwichResolver
  },
  {
    typeDefs: breadType,
    resolvers: breadResolver
  },
  {
    typeDefs: queryType
  }
]);

[khacnha]

I got this error, it always returns null. Unable to connect to resolvers.

Does anyone have a better solution to this problem.

typeDefs.js
module.exports = [
    customScalarResolver,
    pageResolvers,
    faqResolvers,
];

resolvers .js
module.exports = [
  linkSchema,
  pageSchema,
   faqSchema,
];

server.js
buildFederatedSchema([{ typeDefs, resolvers }])

UPDATE 10/01/2020

My solution:

schema: buildFederatedSchema([
        { typeDefs: typeDefs.linkSchema , resolvers: resolvers.customScalarResolver },
        { typeDefs: typeDefs.pageSchema , resolvers: resolvers.pageResolvers },
        { typeDefs: typeDefs.faqSchema , resolvers: resolvers.faqResolvers },
        .....
    ]),