Introduction to GraphQL Code Generator

GraphQL Code Generator is a plugin-based tool that helps you get the best out of your GraphQL stack.

From back-end to front-end, GraphQL Code Generator automates the generation of:

Typed Queries, Mutations and, Subscriptions for React, Vue, Angular, Next.js, Svelte, whether you are using Apollo Client, URQL or, React Query.
Typed GraphQL resolvers, for any Node.js (GraphQL Yoga, GraphQL Modules, TypeGraphQL or Apollo) or Java GraphQL server.
Fully-typed Node.js SDKs, Apollo Android support, and more!

The perfect GraphQL Developer Experience

To illustrate how GraphQL Code Generator improves your developer experience, let’s take a look at the front-end and back-end usage of the following schema:

schema.graphql

type Author {
  id: Int!
  firstName: String!
  lastName: String!
  posts(findTitle: String): [Post]
}
 
type Post {
  id: Int!
  title: String!
  author: Author
}
 
type Query {
  posts: [Post]
}

The following sections showcase why GraphQL Code Generator is a game-changer for your GraphQL Stack.

From the Frontend

Most client-side implementations without GraphQL Code Generator would query the API as showcased in the following examples:

import { useQuery } from 'urql'
 
interface PostsQuery {
  posts: {
    id: string
    title: string
    author?: {
      id: string
      firstName: string
      lastName: string
    }
  }[]
}
 
const postsQueryDocument = /* GraphQL */ `
  query Posts {
    posts {
      id
      title
      author {
        id
        firstName
        lastName
      }
    }
  }
`
 
const Posts = () => {
  const [result] = useQuery<PostsQuery>({ query: postsQueryDocument })
 
  // …
}

import { request, gql } from 'graphql-request'
import { useQuery } from '@tanstack/react-query'
 
interface PostsQuery {
  posts: {
    id: string
    title: string
    author?: {
      id: string
      firstName: string
      lastName: string
    }
  }[]
}
 
const postsQueryDocument = gql`
  query Posts {
    posts {
      id
      title
      author {
        id
        firstName
        lastName
      }
    }
  }
`
 
const Posts = () => {
  const { data } = useQuery<PostsQuery>('posts', async () => {
    const { posts } = await request(endpoint, postsQueryDocument)
    return posts
  })
 
  // …
}

<template>
  <div class="apollo">
    <!-- UI … -->
  </div>
</template>
 
<script lang="ts">
interface PostQueryVariables {
  id: string
}
 
export default {
  apollo: {
    post: {
      query: gql`
        query ($id: ID!) {
          post(id: $id) {
            id
            title
            author {
              id
              firstName
              lastName
            }
          }
        }
      `,
      variables: { id: 1 } as PostQueryVariables
    }
  },
  data() {
    return {
      post: undefined
    }
  }
}
</script>

const GET_POSTS = gql`
  query Posts {
    posts {
      id
      title
      author {
        id
        firstName
        lastName
      }
    }
  }
`
 
interface Post {
  id: string
  title: string
  author?: {
    id: string
    firstName: string
    lastName: string
  }
}
 
@Component({ /* … */ })
class PostsComponent implements OnInit, OnDestroy {
  posts: Post[]
 
  private querySubscription: Subscription
 
  ngOnInit() {
    this.querySubscription = this.apollo
      .watchQuery({ query: GET_POSTS })
      .valueChanges.subscribe(({ data }) => {
        this.posts = data.posts as Post[]
      })
  }
  ngOnDestroy() {
    this.querySubscription.unsubscribe()
  }
}

<script lang="ts">
  import { query } from 'svelte-apollo'
 
  const postsQueryDocument = gql`
    query Posts {
      posts {
        id
        title
        author {
          id
          firstName
          lastName
        }
      }
    }
  `
 
  const posts = query(postsQueryDocument)
</script>
 
<ul>
  <!-- UI … -->
</ul>

Manually maintaining the GraphQL operation types or the complete absence of types can lead to many issues:

outdated typing (regarding the current Schema)
typos
partial typing of data (not all Schema’s fields has a corresponding type)

The strength of your frontend application types is based on your data types. Any mistake on your manually maintained data types ripples in many of your components.

For this reason, automating and generating the typing of your GraphQL operations will both improve the developer experience and stability of your stack.

After installing GraphQL Code Generator:

npm i graphql
npm i -D typescript @graphql-codegen/cli

pnpm add graphql
pnpm add -D typescript @graphql-codegen/cli

yarn add graphql
yarn add --dev typescript @graphql-codegen/cli

bun add graphql
bun add --dev typescript @graphql-codegen/cli

and providing a simple configuration:

codegen.ts

import type { CodegenConfig } from '@graphql-codegen/cli'
 
const config: CodegenConfig = {
   schema: 'https://localhost:4000/graphql',
   documents: ['src/**/*.tsx'],
   generates: {
      './src/gql/': {
        preset: 'client',
      }
   }
}
export default config

You will no longer need to maintain TypeScript types:

import { useQuery } from 'urql'
import { graphql } from './gql/gql'
 
// postsQueryDocument is now fully typed!
const postsQueryDocument = graphql(/* GraphQL */ `
  query Posts {
    posts {
      id
      title
      author {
        id
        firstName
        lastName
      }
    }
  }
`)
 
const Posts = () => {
  // URQL's `useQuery()` knows how to work with typed graphql documents
  const [result] = useQuery({ query: postsQueryDocument })
 
  // `result` is fully typed!
  // …
}

import { request } from 'graphql-request'
import { useQuery } from '@tanstack/react-query'
import { graphql } from './gql/gql'
 
// postsQueryDocument is now fully typed!
const postsQueryDocument = graphql(/* GraphQL */ `
  query Posts {
    posts {
      id
      title
      author {
        id
        firstName
        lastName
      }
    }
  }
`)
 
const Posts = () => {
  // React Query `useQuery()` knows how to work with typed graphql documents
  const { data } = useQuery<PostsQuery>('posts', async () => {
    const { posts } = await request(endpoint, postsQueryDocument)
    return posts
  })
 
  // `data` is fully typed!
  // …
}

<script setup lang="ts">
import { useQuery } from '@vue/apollo-composable';
import { graphql } from './gql/gql';
import FilmItem from './components/FilmItem.vue';
import { computed } from 'vue';
const { result } = useQuery(
  graphql(/* GraphQL */ `
    query Posts {
      posts {
        id
        title
        author {
          id
          firstName
          lastName
        }
      }
    }
  `),
);
 
// `posts` is properly typed!
const posts = computed(() => result.value?.posts);
</script>
 
<template>
  <ul>
    <li v-for="film of films"><FilmItem :film="film" /></li>
  </ul>
</template>

import { PostsGQL, PostsQuery } from './graphql'
import { Observable } from 'rxjs'
import { map } from 'rxjs/operators'
 
@Component({ /* … */ })
export class PostsComponent {
  posts: Observable<PostsQuery['posts']>
 
  constructor(postsGQL: PostsGQL) {
    this.posts = postsGQL.watch().valueChanges.pipe(map(result => result.data.posts))
  }
}

<script lang="ts">
  import { Posts } from '../graphql/generated'
 
  // `posts` is fully typed, also are `Posts()` options!
  const posts = Posts()
</script>
 
<ul>
  <!-- UI … -->
</ul>

Now, with simple configuration and an npm/yarn script, a front-end developer benefits from:

up-to-date typings
autocompletion on all queries, mutations and, subscription variables and results
less boilerplate (thanks to full code generation such as React hooks generation)

💡

Operations and fragments must have unique names

GraphQL Code Generator checks for this automatically and will let you know if you have any conflicts.

💡

How does GraphQL Code Generator work?

More details on the inner working of GraphQL Code Generator are available on this page.

To the Backend

Most GraphQL API resolvers remain untyped or wrongly typed which, leads to multiple issues:

resolvers are not compliant with the schema definition
typos in the resolvers’ function type signature

For this reason, GraphQL Code Generator provides multiple plugins that help you automate the generation of resolvers’ typings.

Here are an example of a GraphQL API leveraging GraphQL Code Generator resolvers typings (based on the schema.graphql above):

import { readFileSync } from 'node:fs'
import { ApolloServer } from 'apollo-server'
import { Resolvers } from './resolvers-types'
 
const typeDefs = readFileSync('./schema.graphql', 'utf8')
 
const resolvers: Resolvers = {
  Query: {
    // typed resolvers!
  }
}
 
const server = new ApolloServer({ typeDefs, resolvers })
 
// The `listen` method launches a web server
server.listen().then(({ url }) => {
  console.log(`🚀  Server ready at ${url}`)
})

import { readFileSync } from 'node:fs'
import { createServer } from 'node:http'
import { createYoga, createSchema } from 'graphql-yoga'
import { Resolvers } from './resolvers-types'
 
const typeDefs = readFileSync('./schema.graphql', 'utf8')
 
const resolvers: Resolvers = {
  Query: {
    // typed resolvers!
  }
}
 
const schema = createSchema({ typeDefs, resolvers })
const yoga = createYoga({ schema })
const server = createServer(yoga)
 
server.listen(4000, () => {
  console.log('GraphQL Server is listening on http://localhost:4000/graphql');
})

Given the following structure:

- src/
  - modules/
    - user/
      - resolvers.ts
      - typedefs/
        - user.graphql
    - product/
      - resolvers.ts
      - typedefs/
        - product.graphql

The User module resolvers would be:

src/modules/user/resolvers.ts

import { UsersModule } from './generated-types/module-types'
 
export const resolvers: UsersModule.Resolvers = {
  // Here, you can implement only the types and fields defined in your module!
}

What’s next?

After unstanding the basic concepts of GraphQL Code Generator, you can start setting it up within your project. If your stack is not listed below, please refer to our plugin overview.

Client-Side GraphQL

Choose your existing setup or preference to get started.

Vanilla TypeScript React Query React / Vue Angular Svelte

Server-Side GraphQL

GraphQL Yoga with Server Preset Apollo Server with Server Preset Apollo and Yoga server GraphQL Modules

Troubleshooting

If you are experiencing any issues, you can reach us via the following channels:

Found a bug? report it in our GitHub repo
Need help or have a question? You can use the live chat box in the corner of the screen, ask it in our GitHub Discussions page or reach out to us directly in our Discord
We have more awesome open source tools!
You can visit our website for more information about us and what we do

Installation