GraphQL: Modern API Query Language

What is GraphQL?

GraphQL is a query language and runtime for APIs that provides a complete and understandable description of the data in your API. Developed by Facebook in 2012 and open-sourced in 2015, GraphQL gives clients the power to ask for exactly what they need and nothing more.

Unlike REST APIs where you might need multiple round-trips to fetch related data, GraphQL allows you to get many resources in a single request, while providing strong type safety and excellent developer tooling.

GraphQL Performance Calculator

GraphQL Core Concepts

type User {
  id: ID!
  name: String!
  posts: [Post!]!
}

query {
  user(id: "123") {
    name
    posts { title }
  }
}

mutation {
  createPost(input: {
    title: "Hello World"
  }) { id title }
}

subscription {
  messageAdded(room: "chat") {
    id content author
  }
}

Advanced GraphQL Patterns

const userLoader = new DataLoader(async (userIds) => {
  const users = await getUsersByIds(userIds);
  return userIds.map(id => users.find(u => u.id === id));
});

# User Service
type User @key(fields: "id") {
  id: ID!
  name: String!
}

# Posts Service
extend type User @key(fields: "id") {
  id: ID! @external
  posts: [Post!]!
}

type Query {
  posts(first: Int, after: String): PostConnection
}

type PostConnection {
  edges: [PostEdge!]!
  pageInfo: PageInfo!
}

Real-World GraphQL Implementations

GraphQL Best Practices