GraphQL Cheatsheet — The Complete Developer Reference

GraphQL is a powerful query language for APIs developed by Facebook, allowing clients to request exactly the data they need and nothing more.
Unlike REST APIs, GraphQL lets you fetch multiple resources in a single request, improving performance and flexibility for modern web and mobile apps.

This GraphQL Cheatsheet is your ultimate quick reference guide to all essential syntax, queries, mutations, subscriptions, and schema definitions — perfect for developers who want to master GraphQL fast.

What is GraphQL?

GraphQL is a data query and manipulation language for APIs, as well as a runtime for fulfilling queries with your existing data.
It provides a strongly typed schema that defines how clients can access your API.

✅ Key Advantages of GraphQL:

• Fetch multiple resources in one query
• No over-fetching or under-fetching
• Strong typing system
• Real-time data with subscriptions
• Perfect for microservices and frontend apps

Basic GraphQL Syntax

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GraphQL Query Example

A query is used to read or fetch data.

query {
  user(id: 1) {
    id
    name
    email
    posts {
      title
      content
    }
  }
}

✅ Output:

{
  "data": {
    "user": {
      "id": 1,
      "name": "Alice",
      "email": "alice@example.com",
      "posts": [
        { "title": "Intro to GraphQL", "content": "GraphQL basics..." }
      ]
    }
  }
}

GraphQL Mutation Example

A mutation is used to create, update, or delete data.

mutation {
  createUser(name: "John", email: "john@example.com") {
    id
    name
    email
  }
}

✅ Output:

{
  "data": {
    "createUser": {
      "id": "2",
      "name": "John",
      "email": "john@example.com"
    }
  }
}

GraphQL Schema Definition Language (SDL)

A schema defines the structure of data and operations available in 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
}

type Mutation {
  createUser(name: String!, email: String!): User
}

GraphQL Fragments

Fragments help reuse field selections across multiple queries.

fragment userDetails on User {
  id
  name
  email
}

query {
  users {
    ...userDetails
  }
}

GraphQL Directives

Directives modify query execution dynamically.

query GetUsers($showEmail: Boolean!) {
  users {
    name
    email @include(if: $showEmail)
  }
}

GraphQL Variables

query getUser($userId: ID!) {
  user(id: $userId) {
    name
    email
  }
}

Variables:

{
  "userId": "1"
}

GraphQL Subscriptions (Real-Time Updates)

Subscriptions allow you to receive live data updates when events occur.

subscription {
  postAdded {
    id
    title
    content
  }
}

GraphQL vs REST API

GraphQL Common Use Cases

• Web and mobile APIs
• Microservice communication
• Real-time dashboards
• Cross-platform applications
• Data aggregation from multiple sources

Error Handling in GraphQL

{
  "errors": [
    {
      "message": "User not found",
      "locations": [{ "line": 2, "column": 3 }],
      "path": ["user"]
    }
  ]
}

GraphQL Tools and Libraries

PostgreSQL Integration with GraphQL

GraphQL can integrate directly with PostgreSQL using:

• Hasura GraphQL Engine
• PostGraphile
• Prisma

Example query:

query {
  users {
    id
    name
    posts {
      title
    }
  }
}

Performance Optimization Tips

• Use query caching for frequent requests.
• Avoid deep nested queries to prevent recursion.
• Implement batch resolvers to reduce round trips.
• Use pagination for large datasets (limit, offset).

FAQ — GraphQL Cheatsheet

Q1: What is GraphQL used for?
GraphQL is used to efficiently fetch and manipulate data from APIs using a single endpoint.

Q2: Is GraphQL faster than REST?
Yes, because it eliminates multiple endpoint calls and reduces payload size.

Q3: Can I use GraphQL with PHP or Python?
Yes, libraries like Lighthouse (PHP) and Graphene (Python) support GraphQL.

Q4: Does GraphQL replace REST?
Not necessarily. It complements REST by providing more flexible querying capabilities.

Q5: How do I test GraphQL queries?
Use GraphiQL, Apollo Studio, or Postman GraphQL mode.