GraphQL Implementation

Build GraphQL APIs with proper schema design, resolvers, and performance optimization.

Schema Definition

type User {
  id: ID!
  name: String!
  email: String!
  posts(limit: Int = 10): [Post!]!
}

type Post {
  id: ID!
  title: String!
  content: String!
  author: User!
  createdAt: DateTime!
}

type Query {
  user(id: ID!): User
  users(limit: Int, offset: Int): [User!]!
  post(id: ID!): Post
}

type Mutation {
  createUser(input: CreateUserInput!): User!
  createPost(input: CreatePostInput!): Post!
}

input CreateUserInput {
  name: String!
  email: String!
}

Apollo Server Setup

const { ApolloServer } = require('@apollo/server');
const { startStandaloneServer } = require('@apollo/server/standalone');

const resolvers = {
  Query: {
    user: (_, { id }, { dataSources }) =>
      dataSources.userAPI.getUser(id),
    users: (_, { limit, offset }, { dataSources }) =>
      dataSources.userAPI.getUsers({ limit, offset })
  },
  User: {
    posts: (user, { limit }, { dataSources }) =>
      dataSources.postAPI.getPostsByUser(user.id, limit)
  },
  Mutation: {
    createUser: (_, { input }, { dataSources }) =>
      dataSources.userAPI.createUser(input)
  }
};

const server = new ApolloServer({ typeDefs, resolvers });

DataLoader for N+1 Prevention

const DataLoader = require('dataloader');

const userLoader = new DataLoader(async (ids) => {
  const users = await User.find({ _id: { $in: ids } });
  return ids.map(id => users.find(u => u.id === id));
});

Error Handling

const { GraphQLError } = require('graphql');

throw new GraphQLError('User not found', {
  extensions: { code: 'NOT_FOUND', argumentName: 'id' }
});

Best Practices

• Use DataLoader to batch queries
• Implement query complexity limits
• Design schema around client needs
• Validate all inputs
• Use descriptive naming conventions

Python Graphene

See [references/python-graphene.md](references/python-graphene.md) for complete Flask implementation with:

• ObjectType definitions
• Query and Mutation classes
• Input types
• Flask integration

Best Practices

Do:

• Use DataLoader to batch queries
• Implement query complexity limits
• Design schema around client needs
• Validate all inputs
• Use descriptive naming conventions
• Add subscriptions for real-time data

Don't:

• Allow deeply nested queries without limits
• Expose database internals
• Ignore N+1 query problems
• Return unauthorized data
• Skip input validation