2nd/10_Wiki/Topics/Frontend/GraphQL-Code-Generator.md

---
id: wiki-2026-0508-graphql-code-generator
title: GraphQL Code Generator
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [graphql-codegen, GQL Codegen, Type-safe GraphQL]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [graphql, typescript, codegen, type-safety]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: typescript
  framework: graphql
---

# GraphQL Code Generator

## 매 한 줄
> **"매 schema → typed client 의 자동화"**. `.graphql` schema + operation 으로부터 TypeScript types, hook, fragment 의 생성. 매 schema drift 의 compile-time 차단 — `any` 의 X, `User.email` typo 의 즉시 error.

## 매 핵심

### 매 핵심 plugin
- **typescript**: schema → TS types (scalar, enum, input, object).
- **typescript-operations**: query/mutation operation → typed result.
- **typed-document-node**: TypedDocumentNode (apollo-client / urql 의 input).
- **client-preset** (modern, 2026 default): 매 fragment-masking, persisted-query 의 통합 preset.

### 매 fragment masking
- Component A 가 fragment X 정의 → component B 가 fragment X 의 field 접근 시 compile error.
- 매 over-fetching 의 prevention 강제.

### 매 응용
1. React + Apollo / urql 매 typed hook 자동 생성.
2. Backend schema change 시 client compile error 즉시 감지.
3. Persisted queries (production safety, query whitelisting).

## 💻 패턴

### codegen.ts (client-preset)
```typescript
import { CodegenConfig } from '@graphql-codegen/cli';

const config: CodegenConfig = {
  schema: 'https://api.example.com/graphql',
  documents: ['src/**/*.{ts,tsx}', '!src/gql/**/*'],
  generates: {
    './src/gql/': {
      preset: 'client',
      presetConfig: {
        fragmentMasking: { unmaskFunctionName: 'getFragmentData' },
      },
      config: {
        useTypeImports: true,
        scalars: { DateTime: 'string', UUID: 'string' },
      },
    },
  },
  hooks: { afterAllFileWrite: ['prettier --write'] },
};
export default config;
```

```bash
pnpm graphql-codegen --watch
```

### Operation — typed result
```typescript
// src/components/UserCard.tsx
import { graphql } from '../gql';
import { useQuery } from '@apollo/client';

const USER_QUERY = graphql(`
  query GetUser($id: ID!) {
    user(id: $id) { id name email avatarUrl }
  }
`);

export function UserCard({ id }: { id: string }) {
  const { data } = useQuery(USER_QUERY, { variables: { id } });
  // 매 data?.user 의 type 의 fully inferred
  return <div>{data?.user?.name}</div>;
}
```

### Fragment masking
```typescript
const USER_AVATAR_FRAGMENT = graphql(`
  fragment UserAvatar on User { avatarUrl name }
`);

function Avatar({ user }: { user: FragmentType<typeof USER_AVATAR_FRAGMENT> }) {
  const u = getFragmentData(USER_AVATAR_FRAGMENT, user);
  return <img src={u.avatarUrl} alt={u.name} />;
}

// parent — 매 user 의 email 의 access X (fragment 의 declare X)
function Parent({ user }) {
  return <Avatar user={user} />;
  // user.email 의 access 시 TS error
}
```

### Persisted queries
```typescript
{
  generates: {
    './persisted-operations.json': {
      preset: 'client',
      presetConfig: { persistedDocuments: true },
    },
  },
}
```

```typescript
// runtime — query string 의 X, hash 만 전송
import { createPersistedQueryLink } from '@apollo/client/link/persisted-queries';
const link = createPersistedQueryLink({ generateHash: doc => doc['__meta__']['hash'] });
```

### Custom scalar mapping
```typescript
config: {
  scalars: {
    DateTime: 'string', // ISO 8601
    JSON: 'Record<string, unknown>',
    BigInt: 'string',
  },
}
```

### Watch + CI
```json
{
  "scripts": {
    "codegen": "graphql-codegen",
    "codegen:watch": "graphql-codegen --watch",
    "ci:codegen-check": "graphql-codegen && git diff --exit-code src/gql/"
  }
}
```

### Multi-schema (federation)
```typescript
{
  schema: ['./schema/users.graphql', './schema/products.graphql'],
  // 매 federated graph 의 single typed client
}
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| 새 React + GraphQL | client-preset + fragment masking |
| Apollo Client (legacy) | typescript + typescript-react-apollo |
| urql | client-preset (urql 의 native 지원) |
| Production 보안 | persisted queries 의 enable |
| Backend schema 의 evolve | CI 의 codegen drift check |

**기본값**: client-preset + fragmentMasking, CI 의 codegen drift check.

## 🔗 Graph
- 부모: [[TypeScript]]
- Adjacent: [[OpenAPI-Codegen]]

## 🤖 LLM 활용
**언제**: GraphQL schema 가 있는 TS project, multi-team 의 schema drift 방지, persisted query 도입.
**언제 X**: REST-only, 매 GraphQL schema 의 unstable 한 prototype phase.

## ❌ 안티패턴
- **codegen output 의 manual edit**: 매 next run 시 overwrite, 매 변경 의 lost.
- **fragment 의 component 외 정의**: fragment masking 의 weak — co-location 강제.
- **DateTime 의 `Date` mapping**: GraphQL response 는 string, 매 runtime mismatch 유발.
- **CI 에 codegen drift check 의 X**: schema 의 silent breakage.

## 🧪 검증 / 중복
- Verified (graphql-code-generator.com docs, client-preset migration guide).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — GraphQL Codegen client-preset 패턴 정리 |