Response model declaration in FastAPI - Mini Project: Build & Apply

Response Model Declaration in FastAPI

📖 Scenario: You are building a simple API to share information about books. You want to make sure the API only sends back the right details about each book to users.

🎯 Goal: Create a FastAPI app that defines a response model using pydantic. The API should return book data with only the specified fields.

📋 What You'll Learn

Create a Book model using pydantic.BaseModel with fields title (string) and author (string).

Create a FastAPI app instance called app.

Create a GET endpoint /book that returns a Book instance.

Use the response_model parameter in the route decorator to declare the response model.

💡 Why This Matters

🌍 Real World

APIs often need to send back data in a clear, consistent format. Response models help define exactly what data clients receive.

💼 Career

Knowing how to declare response models in FastAPI is essential for backend developers building reliable and maintainable APIs.

1

Create the Book model

Create a Book class that inherits from pydantic.BaseModel. It should have two string fields: title and author.

FastAPI

# Your code here

Need a hint?

Use class Book(BaseModel): and define title and author as string fields.

2

Create the FastAPI app

Import FastAPI and create an app instance called app.

FastAPI

from pydantic import BaseModel
from fastapi import FastAPI

class Book(BaseModel):
    title: str
    author: str

# Your code here

Need a hint?

Use app = FastAPI() to create the app instance.

3

Create the GET endpoint with response model

Create a GET endpoint /book using @app.get. Use the response_model=Book parameter. The endpoint should return a Book instance with title set to 'The Great Gatsby' and author set to 'F. Scott Fitzgerald'.

FastAPI

from pydantic import BaseModel
from fastapi import FastAPI

class Book(BaseModel):
    title: str
    author: str

app = FastAPI()

# Your code here

Need a hint?

Use @app.get("/book", response_model=Book) and return a Book instance with the given title and author.

4

Complete the FastAPI app

Make sure the full code includes the Book model, the app instance, and the GET endpoint /book with the response model declared.

FastAPI

from pydantic import BaseModel
from fastapi import FastAPI

class Book(BaseModel):
    title: str
    author: str

app = FastAPI()

@app.get("/book", response_model=Book)
def get_book():
    return Book(title='The Great Gatsby', author='F. Scott Fitzgerald')

# Your code here if needed

Need a hint?

Check that all parts are included: model, app, and endpoint with response model.