Model inheritance in FastAPI - Mini Project: Build & Apply

Model Inheritance with FastAPI and Pydantic

📖 Scenario: You are building a simple FastAPI app to manage users. You want to reuse common user data fields by using model inheritance with Pydantic models.

🎯 Goal: Create a base user model and extend it with an inherited model for user creation that adds a password field.

📋 What You'll Learn

Create a base Pydantic model called UserBase with username and email fields

Create a new model called UserCreate that inherits from UserBase and adds a password field

Use FastAPI to create a POST endpoint /users/ that accepts UserCreate data

Return the user data without the password in the response

💡 Why This Matters

🌍 Real World

Model inheritance helps reuse common data structures in web APIs, making code cleaner and easier to maintain.

💼 Career

Understanding Pydantic model inheritance is essential for building scalable FastAPI applications and handling data validation efficiently.

1

Create the base user model

Create a Pydantic model called UserBase with two fields: username of type str and email of type str.

FastAPI

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

# Create UserBase model here

Need a hint?

Use class UserBase(BaseModel): and define username and email as string fields.

2

Add the user creation model with inheritance

Create a new Pydantic model called UserCreate that inherits from UserBase and adds a new field password of type str.

FastAPI

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class UserBase(BaseModel):
    username: str
    email: str

# Create UserCreate model inheriting UserBase here

Need a hint?

Define UserCreate with (UserBase) after the class name and add password: str.

3

Create the POST endpoint to accept user creation data

Add a POST endpoint /users/ to the FastAPI app that accepts a UserCreate model as input in the request body.

FastAPI

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class UserBase(BaseModel):
    username: str
    email: str

class UserCreate(UserBase):
    password: str

# Add POST endpoint /users/ here

Need a hint?

Use @app.post('/users/') decorator and define an async function create_user with parameter user: UserCreate.

4

Return user data without the password

Modify the create_user function to return only the username and email fields from the user object, excluding the password.

FastAPI

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class UserBase(BaseModel):
    username: str
    email: str

class UserCreate(UserBase):
    password: str

@app.post('/users/')
async def create_user(user: UserCreate):
    # Return only username and email here
    # Your code here

Need a hint?

Return a dictionary with keys username and email from the user parameter.