graphql

GraphQL — Apollo Federation, Schema Design

API GraphQL moderne avec federation, DataLoader, optimisations.

GraphQL vs REST

GraphQL — 1 query sur-mesure, no versioning, introspection auto
REST — Multiple endpoints, over-fetching, v1/v2/v3

Apollo Federation

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

# Orders service
extend type User @key(fields: "id") {
  id: ID! @external
  orders: [Order!]!
}

Gateway compose automatiquement les services.

N+1 Problem — DataLoader

// ❌ N+1 queries
User: { orders: (u) => db.orders.findByUserId(u.id) }

// ✅ DataLoader batch
const loader = new DataLoader(async (ids) => {
  const orders = await db.orders.findByUserIds(ids);
  return ids.map(id => orders.filter(o => o.userId === id));
});
User: { orders: (u) => loader.load(u.id) }

Patterns

Pagination (Relay)

type UserConnection {
  edges: [{ node: User!, cursor: String! }]!
  pageInfo: { hasNextPage: Boolean!, endCursor: String }!
}

Error Handling

type CreateUserPayload {
  user: User
  errors: [{ field: String, message: String! }]
}

Optimizations

DataLoader — Batch + cache
Persisted Queries — Hash lookup
Depth Limiting — Anti-DoS
Cost Analysis — Query budget

---

Voir @api-designer pour design