GraphQL Cheat Sheet

Covers GraphQL schema definition, queries, mutations, resolvers, and common patterns like fragments and batching for flexible APIs.

2 PagesIntermediateFeb 28, 2026

Schema Definition Language

Defining types, queries, mutations, and subscriptions.

graphql

type Book {  id: ID!  title: String!  author: Author!  publishedYear: Int}type Author {  id: ID!  name: String!  books: [Book!]!}type Query {  books: [Book!]!  book(id: ID!): Book}type Mutation {  addBook(title: String!, authorId: ID!): Book!}type Subscription {  bookAdded: Book!}

Queries & Mutations

Fetching and writing data with variables, aliases, and fragments.

graphql

# Query with variables and nested field selectionquery GetBook($id: ID!) {  book(id: $id) {    title    author {      name    }  }}# Mutationmutation AddNewBook {  addBook(title: "Dune", authorId: "42") {    id    title  }}# Aliases and fragmentsquery {  dune: book(id: "1") { ...BookFields }  hobbit: book(id: "2") { ...BookFields }}fragment BookFields on Book {  title  publishedYear}

Resolver Example

Apollo Server-style resolver map, including a nested field resolver.

javascript

const resolvers = {  Query: {    books: (parent, args, context) => context.db.books.findAll(),    book: (parent, { id }, context) => context.db.books.findById(id),  },  Mutation: {    addBook: (parent, { title, authorId }, context) =>      context.db.books.create({ title, authorId }),  },  Book: {    // Nested resolver to resolve the author field    author: (book, args, context) => context.db.authors.findById(book.authorId),  },};

Core Concepts

Vocabulary every GraphQL API relies on.

Query- Read-only operation; client specifies the exact shape of the response
Mutation- Operation that writes/modifies data on the server
Subscription- Long-lived operation that streams updates, typically over WebSockets
Resolver- Function that returns the data for one specific field in the schema
Schema- Strongly-typed contract (SDL) defining every possible query, mutation, and type
N+1 problem- Naive resolvers issuing one DB query per item; fixed with batching (DataLoader)
Introspection- Ability to query the schema itself, used by tools like GraphiQL

Pro Tip

Use DataLoader (or an equivalent per-request batching cache) inside resolvers to avoid the N+1 query problem — without it, fetching 100 books' authors triggers 100 separate database round-trips.

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