GRAPHQL Codegen

GraphQL Code Generator Skill

Type-safe GraphQL with automatic code generation

Overview

Learn to use GraphQL Code Generator to automatically generate TypeScript types, React hooks, and more from your GraphQL schema and operations.

Quick Reference

Setup

1. Installation

npm install -D @graphql-codegen/cli \
  @graphql-codegen/typescript \
  @graphql-codegen/typescript-operations \
  @graphql-codegen/typescript-react-apollo \
  @parcel/watcher

2. Configuration

// codegen.ts
import type { CodegenConfig } from '@graphql-codegen/cli';

const config: CodegenConfig = {
  // Schema source
  schema: 'http://localhost:4000/graphql',

  // Operations to generate from
  documents: ['src/**/*.graphql', 'src/**/*.tsx'],

  // Output
  generates: {
    './src/generated/graphql.ts': {
      plugins: [
        'typescript',
        'typescript-operations',
        'typescript-react-apollo',
      ],
      config: {
        // Custom scalars
        scalars: {
          DateTime: 'string',
          JSON: 'Record<string, unknown>',
        },
        // Generate hooks
        withHooks: true,
        // Use enums as types
        enumsAsTypes: true,
      },
    },
  },
};

export default config;

3. Scripts

{
  "scripts": {
    "codegen": "graphql-codegen --config codegen.ts",
    "codegen:watch": "graphql-codegen --config codegen.ts --watch"
  }
}

Usage Examples

1. Define Operations

# src/graphql/queries.graphql
query GetUser($id: ID!) {
  user(id: $id) {
    id
    name
    email
  }
}

query GetUsers($first: Int!, $after: String) {
  users(first: $first, after: $after) {
    edges {
      node {
        ...UserFields
      }
    }
    pageInfo {
      hasNextPage
      endCursor
    }
  }
}

fragment UserFields on User {
  id
  name
  email
  avatar
}

# src/graphql/mutations.graphql
mutation CreateUser($input: CreateUserInput!) {
  createUser(input: $input) {
    user {
      ...UserFields
    }
    errors {
      field
      message
    }
  }
}

2. Use Generated Code

// Types and hooks are generated
import {
  useGetUserQuery,
  useGetUsersQuery,
  useCreateUserMutation,
  UserFieldsFragment,
  GetUserQuery,
} from '../generated/graphql';

// Query with full type safety
function UserProfile({ userId }: { userId: string }) {
  const { data, loading, error } = useGetUserQuery({
    variables: { id: userId }, // Type-checked!
  });

  if (loading) return <Spinner />;
  if (error) return <Error />;

  // data.user is fully typed
  return <div>{data?.user?.name}</div>;
}

// Mutation with type safety
function CreateUser() {
  const [createUser] = useCreateUserMutation({
    update(cache, { data }) {
      // data is typed
      if (data?.createUser.user) {
        // ...
      }
    },
  });

  const handleSubmit = (input: CreateUserInput) => {
    createUser({ variables: { input } }); // Type-checked!
  };
}

// Fragment type
function UserCard({ user }: { user: UserFieldsFragment }) {
  return <div>{user.name}</div>; // Typed fields
}

Advanced Config

Multiple Outputs

const config: CodegenConfig = {
  schema: 'http://localhost:4000/graphql',
  documents: 'src/**/*.graphql',

  generates: {
    // Types only
    './src/types.ts': {
      plugins: ['typescript'],
    },

    // Operations with type imports
    './src/operations.ts': {
      preset: 'import-types',
      presetConfig: { typesPath: './types' },
      plugins: ['typescript-operations'],
    },

    // Hooks
    './src/hooks.ts': {
      preset: 'import-types',
      presetConfig: { typesPath: './types' },
      plugins: ['typescript-react-apollo'],
    },

    // Near-operation files
    './src/': {
      preset: 'near-operation-file',
      presetConfig: {
        extension: '.generated.tsx',
        baseTypesPath: 'types.ts',
      },
      plugins: ['typescript-operations', 'typescript-react-apollo'],
    },
  },
};

Client Preset (Recommended)

const config: CodegenConfig = {
  schema: 'http://localhost:4000/graphql',
  documents: 'src/**/*.tsx',

  generates: {
    './src/gql/': {
      preset: 'client',
      config: {
        fragmentMasking: { unmaskFunctionName: 'getFragmentData' },
      },
    },
  },
};

// Usage
import { gql, getFragmentData } from '../gql';

const UserQuery = gql(`
  query GetUser($id: ID!) {
    user(id: $id) {
      ...UserAvatar
    }
  }
`);

const UserAvatarFragment = gql(`
  fragment UserAvatar on User {
    avatar
  }
`);

function Profile({ userId }) {
  const { data } = useQuery(UserQuery, { variables: { id: userId } });
  const avatar = getFragmentData(UserAvatarFragment, data?.user);
}

Troubleshooting

Debug

# Validate schema access
curl http://localhost:4000/graphql \
  -H "Content-Type: application/json" \
  -d '{"query":"{ __schema { types { name } } }"}'

# Verbose codegen
npx graphql-codegen --verbose

# Check config
npx graphql-codegen --check

Usage

Skill("graphql-codegen")

Related Skills

• graphql-fundamentals - Schema syntax
• graphql-apollo-client - Using generated hooks
• graphql-schema-design - Better types

Related Agent

• 07-graphql-codegen - For detailed guidance