GraphQl in NodeJs - Resolver for Object Types

Question

I am just getting started with GraphQl in NodeJs. I understand where the resolvers for type goes as coded in below sample.

But I am unable to figure out where the resolver goes for relation Types. for example, Type Book below has a property author which is supposed to return Author type if queried. Where do I put the resolver to resolve this author for the book?

// Construct a schema, using GraphQL schema language
var schema = buildSchema(`  
  type Book {
      id: ID!
      name: String!
      genre: String!
      author: Author
  }
  type Author {
      id: ID!
      name: String!
      age: String!
  }

  type Query {
      books: [Book]
      authors: [Author]
      book(id: ID): Book
      author(id: ID): Author
  }
`);

const root = {
    books: () => {
        return Book.find({});
    },
    authors: () => {
        return Author.find({});
    },
    book:({id}) => {
        return Book.findById(id);
    },
    author:({id}) => {
        return Author.findById(id);
    }
}

const app = express()
app.listen(5000, () =>{
   console.log('listening for request');
})

app.use('/graphql', graphqlHTTP({
    schema: schema,
    rootValue: root,
    graphiql: true
}))

I believe so. I use this rootValue: root when setting graphqlHTTP as middleware for express. I am expanding on these examples graphql.org/graphql-js/running-an-express-graphql-server — Ankit
– Ankit, Commented Nov 21, 2019 at 14:19
The official docs are pretty lacking at the moment. You really shouldn't be using buildSchema in the first place. — Daniel Rearden
– Daniel Rearden, Commented Nov 21, 2019 at 14:59
@DanielRearden awesome. You gave me exactly what I was looking for. That cleared a lot of my questions. Thanks — Ankit
– Ankit, Commented Nov 22, 2019 at 8:41

Dan Starns · Accepted Answer · 2019-11-21 14:44:08Z

You would need to define specific resolvers for the Book type. I would suggest going and grabbing makeExecutableSchema from graphql-tools this way you can easily build the relation resolvers you require. I have copied and change your solution to achieve the desired outcome.

const graphqlHTTP = require("express-graphql")
const express = require("express");
const { makeExecutableSchema } = require("graphql-tools")

const typeDefs = `  
  type Book {
      id: ID!
      name: String!
      genre: String!
      author: Author
  }
  type Author {
      id: ID!
      name: String!
      age: String!
  }

  type Query {
      books: [Book]
      authors: [Author]
      book(id: ID): Book
      author(id: ID): Author
  }
`;

const resolvers = {
    Book: {
        author: (rootValue, args) => {
            // rootValue is a resolved Book type.

            return {
                id: "id",
                name: "dan",
                age: "20"
            }
        }
    },
    Query: {
        books: (rootValue, args) => {
            return [{ id: "id", name: "name", genre: "shshjs" }];
        },
        authors: (rootValue, args) => {
            return Author.find({});
        },
        book: (rootValue, { id }) => {
            return Book.findById(id);
        },
        author: (rootValue, { id }) => {
            return Author.findById(id);
        }
    }
}

const app = express();

app.listen(5000, () => {
    console.log('listening for request');
})

app.use('/graphql', graphqlHTTP({
    schema: makeExecutableSchema({ typeDefs, resolvers }),
    graphiql: true
}))

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