server.js

const {
  GraphQLSchema,
  GraphQLObjectType,
  GraphQLString,
  GraphQLList,
  GraphQLInt,
  GraphQLNonNull,
} = require("graphql");

const authors = [
  { id: 1, name: "J. K. Rowling" },
  { id: 2, name: "J. R. R. Tolkien" },
  { id: 3, name: "Brent Weeks" },
];

const books = [
  { id: 1, name: "Harry Potter and the Chamber of Secrets", authorId: 1 },
  { id: 2, name: "Harry Potter and the Prisoner of Azkaban", authorId: 1 },
  { id: 3, name: "Harry Potter and the Goblet of Fire", authorId: 1 },
  { id: 4, name: "The Fellowship of the Ring", authorId: 2 },
  { id: 5, name: "The Two Towers", authorId: 2 },
  { id: 6, name: "The Return of the King", authorId: 2 },
  { id: 7, name: "The Way of Shadows", authorId: 3 },
  { id: 8, name: "Beyond the Shadows", authorId: 3 },
];

const express = require("express");
require("dotenv").config();
const { graphqlHTTP } = require("express-graphql");
const app = express();
const port = process.env.PORT || 5000;

const RootMutationType = new GraphQLObjectType({
  name: "Mutation",
  description: "Root Mutation",
  fields:() => ({
    addBook:{
      type:BookType,
      description:'Add a book',
      args:{
        name:{type: GraphQLNonNull(GraphQLString)},
        authorId:{type: GraphQLNonNull(GraphQLInt)}
      },
      resolve:(parent,args) => {
        const book = {id:books.length + 1, name:args.name, authorId:args.authorId}
        books.push(book)
        return book
      }
    },
    addAuthor:{
      type:AuthorType,
      description:'Add an author',
      args:{
        name:{type: GraphQLNonNull(GraphQLString)},
      },
      resolve:(parent,args) => {
        const author = {id:authors.length + 1, name:args.name, }
        authors.push(author)
        return author
      }
    },
  })
});

const BookType = new GraphQLObjectType({
  name: "Book",
  description: "This represents a books written by the an autor",
  fields: () => ({
    id: { type: GraphQLNonNull(GraphQLInt) },
    name: { type: GraphQLNonNull(GraphQLString) },
    author: {
      type: AuthorType,
      resolve: (book) => {
        return authors.find((author) => author.id === book.authorId);
      },
    },
  }),
});

const AuthorType = new GraphQLObjectType({
  name: "Author",
  description: "This represendts a author",
  fields: () => ({
    id: { type: GraphQLNonNull(GraphQLInt) },
    name: { type: GraphQLNonNull(GraphQLString) },
    books: {
      type: new GraphQLList(BookType),
      resolve: (author) => {
        return books.filter((book) => book.authorId === author.id);
      },
    },
  }),
});

const RootQueryType = new GraphQLObjectType({
  name: "Query",
  description: "Root Query",
  fields: () => ({
    book: {
      type: BookType,
      description: "Single Book",
      args: {
        id: {
          type: GraphQLInt,
        },
      },
      resolve: (parent, args) => books.find((book) => book.id == args.id),
    },
    author: {
      type: AuthorType,
      description: "single Author",
      args: {
        id: {
          type: GraphQLInt,
        },
      },
      resolve: (parent, args) => authors.find((author) => author.id == args.id),
    },
    books: {
      type: new GraphQLList(BookType),
      description: "List of great books",
      resolve: () => books,
    },
    authors: {
      type: new GraphQLList(AuthorType),
      description: "List of great Authors",
      resolve: () => authors,
    },
  }),
});
const schema = new GraphQLSchema({
  query: RootQueryType,
  mutation:RootMutationType
});
app.use(
  "/graphql",
  graphqlHTTP({
    schema: schema,
    graphiql: true,
  })
);

app.listen(port, () => console.log(`Server is listening on port ${port}`));