How to create your first schema in GraphQL

• Scalar fields like: username, commentKarma and createdISO. These are the basic types in the GraphQL schema and they can represent integers, floats, strings or booleans.
• Complex fields like: reddit and user. Fields that represent objects have a custom type, for example, the user field belongs to the RedditUser type (see Figure 2). 

const graphql = require("graphql");
const getBooks = require("./../../data/books");
const getReaders = require("./../../data/readers");

const {
  GraphQLObjectType,
  GraphQLString,
  GraphQLSchema,
  GraphQLID,
  GraphQLInt,
  GraphQLList
} = graphql;

const books = getBooks;
const readers = getReaders;

const BookType = new GraphQLObjectType({
  name: "Book",
  fields: () => ({
    id: { type: GraphQLID },
    name: { type: GraphQLString },
    author: { type: GraphQLString },
    reader: {
      type: ReaderType,
      async resolve(parent, args) {
        const queryResult = await testAsyncFunction(parent);
        console.log("Displayed after return");
        return queryResult;
      }
    }
  })
});

async function testAsyncFunction(parent) {
  return readers.find(reader => reader.id === parent.readerId);
}

const ReaderType = new GraphQLObjectType({
  name: "Reader",
  fields: () => ({
    id: { type: GraphQLID },
    name: { type: GraphQLString },
    age: { type: GraphQLInt },
    books: {
      type: new GraphQLList(BookType),
      resolve(parent, args) {
        return books.filter(book => book.readerId === parent.id);
      }
    }
  })
});

const RootQuery = new GraphQLObjectType({
  name: "RootQueryType",
  fields: {
    book: {
      type: BookType,
      args: { id: { type: GraphQLID } },
      resolve(parent, args) {
        return books.find(book => book.id === args.id);
      }
    },
    reader: {
      type: ReaderType,
      args: { id: { type: GraphQLID } },
      resolve(parent, args) {
        return readers.find(reader => reader.id === args.id);
      }
    },
    books: {
      type: new GraphQLList(BookType),
      resolve(parent, args) {
        return books;
      }
    },
    readers: {
      type: new GraphQLList(ReaderType),
      resolve(parent, args) {
        return readers;
      }
    }
  }Running on port
});

module.exports = new GraphQLSchema({
  query: RootQuery
});

const express = require("express");
const graphqlHTTPS = require("express-graphql");
const schema = require("./schema/schema");

const app = express();

app.use(
  "/graphql",
  graphqlHTTPS({
    schema,
    graphiql: true
  })
);

app.listen(4000, () => {
  console.log("Running on port 4000");
});