GraphQL adalah query language untuk API yang memberikan flexibility dalam request data. Mari pelajari cara menggunakannya.

Apa itu GraphQL?

REST vs GraphQL

REST:
- Multiple endpoints
- Over/under fetching
- Fixed response structure
- Versioning dengan URL
GraphQL:

Single endpoint
Request exact data needed
Flexible response
Schema evolution tanpa versioning

Contoh Comparison

REST - Multiple requests:
GET /users/1
GET /users/1/posts
GET /users/1/followers
GraphQL - Single request:
query {
user(id: 1) {
name
posts {
title
}
followers {
name
}
}
}

Setup GraphQL Server

dengan Node.js dan Apollo Server

# Initialize project
npm init -y
npm install @apollo/server graphql
npm install typescript @types/node ts-node --save-dev
Create tsconfig.json
npx tsc --init

Basic Server

// src/index.ts
import { ApolloServer } from "@apollo/server";
import { startStandaloneServer } from "@apollo/server/standalone";
// Type definitions
const typeDefs = `#graphql
type User {
id: ID!
name: String!
email: String!
posts: [Post!]!
}
type Post {
id: ID!
title: String!
content: String!
author: User!
}
type Query {
users: [User!]!
user(id: ID!): User
posts: [Post!]!
post(id: ID!): Post
}
`;
// Sample data
const users = [
{ id: "1", name: "Budi", email: "[email protected]" },
{ id: "2", name: "Ani", email: "[email protected]" },
];
const posts = [
{ id: "1", title: "First Post", content: "Content 1", authorId: "1" },
{ id: "2", title: "Second Post", content: "Content 2", authorId: "1" },
{ id: "3", title: "Third Post", content: "Content 3", authorId: "2" },
];
// Resolvers
const resolvers = {
Query: {
users: () => users,
user: (
: any, args: { id: string }) =>
users.find((user) => user.id === args.id),
posts: () => posts,
post: (: any, args: { id: string }) =>
posts.find((post) => post.id === args.id),
},
User: {
posts: (parent: { id: string }) =>
posts.filter((post) => post.authorId === parent.id),
},
Post: {
author: (parent: { authorId: string }) =>
users.find((user) => user.id === parent.authorId),
},
};
// Start server
const server = new ApolloServer({
typeDefs,
resolvers,
});
const startServer = async () => {
const { url } = await startStandaloneServer(server, {
listen: { port: 4000 },
});
console.log(
🚀 Server ready at: ${url});
};
startServer();

Schema Definition

Scalar Types

# Built-in scalar types
type Example {
  id: ID! # Unique identifier
  name: String! # UTF-8 string
  age: Int # 32-bit integer
  price: Float # Double-precision float
  active: Boolean # true/false
}
Custom scalar
scalar DateTime
scalar JSON

Object Types

type User {
  id: ID!
  name: String!
  email: String!
  createdAt: DateTime!
  profile: Profile
  posts: [Post!]!
}
type Profile {
bio: String
avatar: String
website: String
}
type Post {
id: ID!
title: String!
content: String!
published: Boolean!
author: User!
tags: [String!]!
comments: [Comment!]!
}
type Comment {
id: ID!
text: String!
author: User!
post: Post!
}

Input Types

input CreateUserInput {
  name: String!
  email: String!
  password: String!
}
input UpdateUserInput {
name: String
email: String
bio: String
}
input PostFilterInput {
published: Boolean
authorId: ID
tag: String
}

Enums

enum Role {
  USER
  ADMIN
  MODERATOR
}
enum PostStatus {
DRAFT
PUBLISHED
ARCHIVED
}
type User {
id: ID!
name: String!
role: Role!
}

Interfaces

interface Node {
  id: ID!
}
interface Timestamped {
createdAt: DateTime!
updatedAt: DateTime!
}
type User implements Node & Timestamped {
id: ID!
name: String!
createdAt: DateTime!
updatedAt: DateTime!
}

Unions

union SearchResult = User | Post | Comment
type Query {
search(term: String!): [SearchResult!]!
}

Queries

Basic Query

# Schema
type Query {
  users: [User!]!
  user(id: ID!): User
  posts(filter: PostFilterInput, limit: Int, offset: Int): [Post!]!
}
Client query
query GetUser {
user(id: "1") {
name
email
posts {
title
}
}
}
Query with variables
query GetUser($userId: ID!) {
user(id: $userId) {
name
email
}
}
Variables
{
"userId": "1"
}

Query with Arguments

# Schema
type Query {
  posts(
    limit: Int = 10
    offset: Int = 0
    published: Boolean
    orderBy: PostOrderBy
  ): [Post!]!
}
enum PostOrderBy {
CREATED_AT_ASC
CREATED_AT_DESC
TITLE_ASC
TITLE_DESC
}
Client query
query GetPosts {
posts(limit: 5, published: true, orderBy: CREATED_AT_DESC) {
id
title
createdAt
}
}

Fragments

# Define fragment
fragment UserBasicInfo on User {
  id
  name
  email
}
fragment PostInfo on Post {
id
title
content
createdAt
}
Use fragments
query GetData {
user(id: "1") {
...UserBasicInfo
posts {
...PostInfo
}
}
}

Aliases

query GetMultipleUsers {
  firstUser: user(id: "1") {
    name
  }
  secondUser: user(id: "2") {
    name
  }
}

Mutations

Basic Mutations

# Schema
type Mutation {
  createUser(input: CreateUserInput!): User!
  updateUser(id: ID!, input: UpdateUserInput!): User
  deleteUser(id: ID!): Boolean!
createPost(input: CreatePostInput!): Post!
publishPost(id: ID!): Post
deletePost(id: ID!): Boolean!
}
input CreateUserInput {
name: String!
email: String!
password: String!
}
input CreatePostInput {
title: String!
content: String!
published: Boolean = false
}
Client mutation
mutation CreateUser($input: CreateUserInput!) {
createUser(input: $input) {
id
name
email
}
}
Variables
{
"input": {
"name": "Budi",
"email": "[email protected]",
"password": "secret123"
}
}

Resolver Implementation

const resolvers = {
  Mutation: {
    createUser: async (_: any, { input }: { input: CreateUserInput }) => {
      const user = await db.user.create({
        data: {
          name: input.name,
          email: input.email,
          password: await hashPassword(input.password),
        },
      });
      return user;
    },
updateUser: async (
  _: any,
  { id, input }: { id: string; input: UpdateUserInput }
) => {
  const user = await db.user.update({
    where: { id },
    data: input,
  });
  return user;
},

deleteUser: async (_: any, { id }: { id: string }) => {
  await db.user.delete({ where: { id } });
  return true;
},
},
};
Subscriptions
Setup Subscriptions
// Install additional dependencies
// npm install graphql-ws ws
import { createServer } from "http";
import { WebSocketServer } from "ws";
import { useServer } from "graphql-ws/lib/use/ws";
import { ApolloServer } from "@apollo/server";
import { expressMiddleware } from "@apollo/server/express4";
import { makeExecutableSchema } from "@graphql-tools/schema";
import { PubSub } from "graphql-subscriptions";
const pubsub = new PubSub();
const typeDefs = 
#graphql
type Subscription {
postCreated: Post!
commentAdded(postId: ID!): Comment!
}
;
const resolvers = {
Subscription: {
postCreated: {
subscribe: () => pubsub.asyncIterator(["POST
CREATED"]),
},
commentAdded: {
subscribe: (: any, { postId }: { postId: string }) => {
return pubsub.asyncIterator([
COMMENT_ADDED_${postId}]);
},
},
},
Mutation: {
createPost: async (_: any, { input }: { input: CreatePostInput }) => {
const post = await db.post.create({ data: input });
pubsub.publish("POST_CREATED", { postCreated: post });
return post;
},
},
};
Client Subscription
subscription OnPostCreated {
  postCreated {
    id
    title
    author {
      name
    }
  }
}
Authentication
Context Setup
import { ApolloServer } from "@apollo/server";
import jwt from "jsonwebtoken";
interface Context {
user?: {
id: string;
role: string;
};
}
const server = new ApolloServer<Context>({
typeDefs,
resolvers,
});
const { url } = await startStandaloneServer(server, {
context: async ({ req }) => {
const token = req.headers.authorization?.replace("Bearer ", "");
if (token) {
  try {
    const user = jwt.verify(token, process.env.JWT_SECRET!) as {
      id: string;
      role: string;
    };
    return { user };
  } catch {
    return {};
  }
}

return {};
},
listen: { port: 4000 },
});
Protected Resolvers
const resolvers = {
  Query: {
    me: (_: any, __: any, context: Context) => {
      if (!context.user) {
        throw new Error("Not authenticated");
      }
      return db.user.findUnique({ where: { id: context.user.id } });
    },
  },
Mutation: {
createPost: (_: any, { input }: any, context: Context) => {
if (!context.user) {
throw new Error("Not authenticated");
}
return db.post.create({
data: {
...input,
authorId: context.user.id,
},
});
},
deleteUser: (_: any, { id }: { id: string }, context: Context) =&gt; {
  if (!context.user || context.user.role !== &quot;ADMIN&quot;) {
    throw new Error(&quot;Not authorized&quot;);
  }
  return db.user.delete({ where: { id } });
},
},
};
Error Handling
Custom Errors
import { GraphQLError } from "graphql";
const resolvers = {
Mutation: {
createUser: async (_: any, { input }: any) => {
const existingUser = await db.user.findUnique({
where: { email: input.email },
});
  if (existingUser) {
    throw new GraphQLError(&quot;Email already exists&quot;, {
      extensions: {
        code: &quot;USER_ALREADY_EXISTS&quot;,
        http: { status: 400 },
      },
    });
  }

  return db.user.create({ data: input });
},
},
};
Error Response
{
  "errors": [
    {
      "message": "Email already exists",
      "locations": [{ "line": 2, "column": 3 }],
      "path": ["createUser"],
      "extensions": {
        "code": "USER_ALREADY_EXISTS"
      }
    }
  ],
  "data": null
}
DataLoader (N+1 Problem)
Install DataLoader
npm install dataloader
Implementation
import DataLoader from "dataloader";
// Batch function
const batchUsers = async (userIds: readonly string[]) => {
const users = await db.user.findMany({
where: { id: { in: [...userIds] } },
});
// Return dalam order yang sama dengan input
const userMap = new Map(users.map((u) => [u.id, u]));
return userIds.map((id) => userMap.get(id) || null);
};
// Create loader per request
const context = async ({ req }: any) => ({
loaders: {
userLoader: new DataLoader(batchUsers),
},
});
// Use in resolver
const resolvers = {
Post: {
author: (parent: any, _: any, context: any) => {
return context.loaders.userLoader.load(parent.authorId);
},
},
};
Best Practices
Schema Design
# Use meaningful names
type User {
  # Good
  createdAt: DateTime!
  updatedAt: DateTime!
Avoid
created: String!
updated: String!
}
Nullable by default, use ! for required
type Post {
id: ID! # Required
title: String! # Required
subtitle: String # Optional
}
Use Input types untuk mutations
input CreateUserInput {
name: String!
email: String!
}
Return object dari mutation (bukan Boolean)
type Mutation {
Good
createUser(input: CreateUserInput!): User!
Avoid
createUser(name: String!, email: String!): Boolean!
}
Performance
// Use DataLoader
// Implement pagination
// Use query complexity analysis
// Cache when appropriate
// Pagination
type Query {
posts(
first: Int
after: String
last: Int
before: String
): PostConnection!
}
type PostConnection {
edges: [PostEdge!]!
pageInfo: PageInfo!
}
type PostEdge {
cursor: String!
node: Post!
}
type PageInfo {
hasNextPage: Boolean!
hasPreviousPage: Boolean!
startCursor: String
endCursor: String
}
Kesimpulan
GraphQL memberikan flexibility dan efficiency dalam API development. Ideal untuk complex data requirements dengan multiple interconnected resources.