"""===========================================================
         goto to https://countries.trevorblades.com/
=============================================================="""
type User{
  id:ID
  name:String
  age:Int
  height:Float
  isMarried:Boolean! """ ======"""
  firends:[User] """======"""
  videosPosted: [Video]
}

type Video {
  id:ID!
  title:String!
  description:String!
}




"""========= """
type Query{
users:[User]
user(id:ID):User 
user(id:ID, name:String ):User
}


"""============query from api ========="""
{
  country(code:"US"){
    code
    name
    capital
    currencies
    phone
    continent{
countries{capital}
      name
    }
  }
}

start graph ql with node js application

npm init -y
npm install apollo-server graphql nodemon
"""create a app file or index.js file"""
""" create a schema folder """
""" insha allahide schema folder create 3 file. 
1. resolvers.js
2. typeDefs.js
3. fakeData.js ==> because we aren't use any database
 """

index.js

const { ApolloServer } = require("apollo-server");
const typeDefs = require("./schema/typeDefs");
const { resolvers } = require("./schema/resolvers");

const server = new ApolloServer({ typeDefs, resolvers });
server
 .listen()
 .then(({ url }) => {
  console.log(`API IS RUNNING ON ${url}`);
 })
 .catch((err) => console.log(err));

typeDefs.js

// get all users 
// get single user
// enum types
const { gql } = require("apollo-server");
const typeDefs = gql`
 type User {
  id: ID!
  name: String!
  userName: String!
  age: Int!
  nationality: Nationality!
  friends: [User]
 }
 type Query {
  users: [User!]!
  user(id: ID!): User!
 }

 enum Nationality { 
  BD
  INDIA
 }
`;
module.exports = typeDefs;

resolvers.js

const { userList } = require("../schema/fakeData");

const resolvers = {
 Query: {
  users() { // all user api
   return userList;
  },
  user(_parent, args) { // single user api
   const user = userList.find((user) => user.id === Number(args.id));
   return user;
  },
 },
};
module.exports = { resolvers };

এই কাজ গুলো করলে আমাদের apollo server রান করার কাজ শেষ হয়ে যাবে । এখন আপনি আপনার ডাটা অ্যাক্সেস করতে পারবেন ড্যাশবোর্ড থেকে । ঠিক এইভাবে

নিয়ম ১ ঃ

নিয়ম ২ ঃ

Mutation

create :

resolvers.js

Mutation: {
  createUser: (parent, args) => {
   const user = args.input;
   userList.push(user);
   return user;
  },
  // update user
  updateUser: (parent, args) => {
   const { id, userName } = args.input;
   const findedUser = userList.find(
    (user) => parseInt(user.id) === parseInt(id)
   );
   findedUser.userName = userName;
   return findedUser;
  },

 },

typeDefs.js

 input CreateUserInput {
  id: ID!
  name: String!
  userName: String!
  age: Int!
  nationality: Nationality!
 }
 input UpdateInput {
  userName: String!
  id: ID!
 }
 type Mutation {
  createUser(input: CreateUserInput!): User!
  updateUser(input: UpdateInput!): User!
 }

this is the process

start graphql on react

1. install apollo client

2. install graphQL

3. npm install @apollo/client graphql

   install command

on react component অথবা যেখানে ইহা কনফিগার করতে চান সেখানে ।

//============= import some package or enything ===============
const { ApolloClient ,InMamoryCache, ApploProvider, useQuery, gql, useLazyQuery} from "@apollo/client"

// ========== this configuration for userQuery hooks==========
const QUERY_ALL_USERS = gql`
    query getAlluser{
      users {
        age
        name
        userName
      }
    }
`
const QUERY_SINGLE_USER = gql`
    query getSingleUser($userId: ID!){
      user(id: $userId) {
       name
       userName 
      }
    }
`
// app component
const App = () =>{
// =========== configuration for graphQL =============
const client = new ApolloClient({
    cache: new InMamoryCache(), 
    uri: "http://localhost:4000/graphql", 
}),
//============== calling api [query] ===================
const { data, loading, error, refetch } = useQuery(QUERY_ALL_USERS)
                             // 👆👆 to fetch data again 

// single user [query] with passing arguemtns [userId]
const [ getSingleUser, {data, loading, error} ]= useLazyQuery(QUERY_SINGLE_USER)

    // ----------if you want to do user can click on the button for   refech api. how can we do that     

const [fatchusers, {data, error}] = useLazyQuery(QUERY_ALL_USERS)
     // 👆👆👆👆👆 it's fetcher function

// ============= calling api [Mutation] ================

    //========================================================
    //                   ======render JSX=====
    //========================================================
return <ApploProvider client={client}>
   <h1>Explore graphQl on React JS</h1>
   <div>
   {
    data
    .users
    .map((user,index) => <div key={index}>{user.name}</div>)
   }
   </div>

<button onClick={() => getSingleUser({ variables:{ userId:1 }})}>get Single user by passing arguemnts</button>

   <button onClick={fatchusers} > Refresh users </button>
</ApploProvider>
}

now ready to work this react application with graphQL api.

same method to update, create and delete Just useMutation will replace useQuery.