api-graphql-grpc

GraphQL & gRPC Skill

Design schemas, resolvers, and service definitions for GraphQL and gRPC APIs.

GraphQL Schema Design

# Scalars
scalar DateTime
scalar UUID
scalar JSON

# Enums
enum OrderStatus { PENDING PAID SHIPPED DELIVERED CANCELLED }
enum UserRole { ADMIN EDITOR VIEWER }

# Types
type User {
  id: UUID!
  name: String!
  email: String!
  role: UserRole!
  orders(first: Int, after: String): OrderConnection!
  createdAt: DateTime!
}

type Order {
  id: UUID!
  status: OrderStatus!
  total: Float!
  items: [OrderItem!]!
  user: User!
  createdAt: DateTime!
}

type OrderItem {
  id: UUID!
  product: Product!
  quantity: Int!
  price: Float!
}

# Pagination (Relay cursor spec)
type OrderConnection {
  edges: [OrderEdge!]!
  pageInfo: PageInfo!
  totalCount: Int!
}
type OrderEdge { node: Order!; cursor: String! }
type PageInfo {
  hasNextPage: Boolean!
  hasPreviousPage: Boolean!
  startCursor: String
  endCursor: String
}

# Queries
type Query {
  me: User
  user(id: UUID!): User
  users(first: Int, after: String, role: UserRole): UserConnection!
  order(id: UUID!): Order
  orders(status: OrderStatus, first: Int, after: String): OrderConnection!
}

# Mutations
type Mutation {
  createUser(input: CreateUserInput!): CreateUserPayload!
  updateUser(id: UUID!, input: UpdateUserInput!): UpdateUserPayload!
  deleteUser(id: UUID!): DeletePayload!
  createOrder(input: CreateOrderInput!): CreateOrderPayload!
  cancelOrder(id: UUID!): CancelOrderPayload!
}

# Subscriptions
type Subscription {
  orderStatusChanged(orderId: UUID!): Order!
  newOrder: Order!
}

# Inputs & Payloads
input CreateUserInput { name: String!; email: String!; role: UserRole }
type CreateUserPayload { user: User; errors: [UserError!] }
type UserError { field: String; message: String! }

Resolver Pattern (DataLoader — solves N+1)

// Without DataLoader: N+1 queries
// With DataLoader: batch all user IDs into one SQL IN(...)

const userLoader = new DataLoader(async (userIds) => {
  const users = await db.query(`SELECT * FROM users WHERE id = ANY($1)`, [userIds]);
  // Return in same order as input IDs
  return userIds.map(id => users.find(u => u.id === id) || null);
});

const resolvers = {
  Order: {
    user: (order, _, { loaders }) => loaders.user.load(order.userId),
  },
  Query: {
    orders: async (_, { status, first = 20, after }) => {
      return paginatedQuery('orders', { status, first, after });
    }
  }
};