GraphQL Proficient¶

🌐 Networking · Level 4

⏱️ ~3 days 📚 Prerequisites: APIs & HTTP, Web Frameworks

When you'd use this

Schema definition, resolvers, queries, mutations and Strawberry framework.

Expose a flexible query API where clients request exactly the fields they need — reducing over- and under-fetching.

GraphQL with Strawberry (Python-native)¶

Define a schema with Python types and let clients query exactly the fields they need.

import strawberry
from strawberry.fastapi import GraphQLRouter
from fastapi import FastAPI

@strawberry.type
class User:
    id: int
    name: str
    email: str
    age: int

@strawberry.type
class Query:
    @strawberry.field
    def user(self, id: int) -> User | None:
        users = {1: User(1, "Alice", "a@b.com", 30), 2: User(2, "Bob", "b@c.com", 25)}
        return users.get(id)

    @strawberry.field
    def users(self) -> list[User]:
        return [User(1, "Alice", "a@b.com", 30), User(2, "Bob", "b@c.com", 25)]

@strawberry.type
class Mutation:
    @strawberry.mutation
    def create_user(self, name: str, email: str, age: int) -> User:
        new_user = User(id=3, name=name, email=email, age=age)
        return new_user

schema = strawberry.Schema(query=Query, mutation=Mutation)

app = FastAPI()
app.include_router(GraphQLRouter(schema), prefix="/graphql")

Querying¶

Shape responses from the client side — one request, precisely the data you want.

# Get specific fields (no over-fetching!)
query {
  user(id: 1) {
    name
    email
  }
}

# Response:
# {"data": {"user": {"name": "Alice", "email": "a@b.com"}}}

# Get multiple resources in one request
query {
  user(id: 1) { name }
  users { id name }
}

# Mutation
mutation {
  createUser(name: "Charlie", email: "c@d.com", age: 35) {
    id
    name
  }
}

REST vs GraphQL¶

When flexible client-driven queries beat fixed REST endpoints (and when they don't).

Feature	REST	GraphQL
Endpoints	Multiple (`/users`, `/posts`)	Single (`/graphql`)
Data shape	Server decides	Client decides
Over-fetching	Common	Impossible
Under-fetching	Requires multiple calls	Single query
Versioning	URL or header	Evolve schema
Best for	Simple CRUD, public APIs	Complex UIs, mobile apps

Practice Exercises¶

Build a GraphQL API for a blog (posts, comments, authors) with Strawberry.
Implement pagination with cursor-based connections.
Add authentication — only logged-in users can mutate data.
Implement DataLoader to solve the N+1 problem in resolvers.
Compare a GraphQL API vs REST API for the same data — measure payload sizes.

💬 Discussion

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