Folder structure patterns in FastAPI

Introduction

Organizing your FastAPI project files helps keep your code clean and easy to find. It makes working on your app simpler and faster.

When starting a new FastAPI project to keep code neat.

When your app grows and you add more features or routes.

When working with a team to avoid confusion about file locations.

When you want to separate different parts like models, routes, and services.

When preparing your app for easier testing and maintenance.

Syntax

FastAPI

project_root/
├── app/
│   ├── main.py
│   ├── models.py
│   ├── routes/
│   │   ├── __init__.py
│   │   ├── users.py
│   │   └── items.py
│   ├── services/
│   │   ├── __init__.py
│   │   └── user_service.py
│   └── database.py
├── tests/
│   ├── test_users.py
│   └── test_items.py
└── requirements.txt

The app/ folder holds your main application code.

Subfolders like routes/ and services/ separate different parts of your app.

Examples

A simple structure with main app file, models, and routes separated.

FastAPI

app/
├── main.py
├── models.py
├── routes/
│   ├── users.py
│   └── items.py

More detailed structure splitting models into their own folder and adding services.

FastAPI

app/
├── main.py
├── models/
│   ├── user.py
│   └── item.py
├── routes/
│   ├── users.py
│   └── items.py
├── services/
│   └── auth.py

A scalable pattern with versioned API, core utilities, database, and models separated.

FastAPI

project_root/
├── app/
│   ├── __init__.py
│   ├── main.py
│   ├── api/
│   │   ├── v1/
│   │   │   ├── __init__.py
│   │   │   ├── users.py
│   │   │   └── items.py
│   ├── core/
│   │   ├── config.py
│   │   └── security.py
│   ├── db/
│   │   ├── base.py
│   │   └── session.py
│   └── models/
│       ├── user.py
│       └── item.py

Sample Program

This is a simple FastAPI app with a root route. The folder structure comment shows how files are organized.

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.get('/')
async def read_root():
    return {"message": "Welcome to the FastAPI app!"}

# Folder structure:
# project_root/
# ├── app/
# │   ├── main.py  (this file)
# │   ├── routes/
# │   │   └── users.py
# │   ├── models.py
# │   └── database.py
# └── requirements.txt

Important Notes

Keep your folder names clear and consistent.

Use __init__.py files to make folders Python packages when needed.

As your app grows, consider splitting code by features or layers (models, routes, services).

Summary

Good folder structure keeps your FastAPI project organized and easy to maintain.

Separate code by purpose: routes, models, services, and database.

Start simple and adjust structure as your app grows.

Practice

1. Which folder is best suited to keep your API endpoint definitions in a FastAPI project?

easy

A. routes

B. models

C. services

D. database

Solution

1. Step 1: Understand folder roles in FastAPI

   The routes folder is typically used to store API endpoint definitions, organizing the paths and HTTP methods.

2. Step 2: Match folder purpose to content

   models is for data models, services for business logic, and database for database connection code.

3. Final Answer:

   routes -> Option A

4. Quick Check:

   API endpoints go in routes [OK]

Hint: API paths belong in routes folder [OK]

Common Mistakes:

• Putting endpoints in models folder
• Mixing database code with routes
• Storing business logic in routes

2. Which of the following is the correct way to organize a FastAPI project folder for database models?

easy

A. Store models in the root project folder

B. Place all models inside a folder named services

C. Keep models mixed with route files

D. Put database models inside a folder named models

Solution

1. Step 1: Identify the folder for data models

   Database models represent data structure and belong in a dedicated models folder for clarity and separation.

2. Step 2: Evaluate other options

   services is for business logic, mixing models with routes or root folder reduces clarity and maintainability.

3. Final Answer:

   Put database models inside a folder named models -> Option D

4. Quick Check:

   Models folder holds data models [OK]

Hint: Models go in models folder, not services or root [OK]

Common Mistakes:

• Confusing services with models
• Mixing models and routes
• Scattering models in root folder

3. Given this FastAPI folder structure:

app/
  routes/
    user.py
  models/
    user.py
  services/
    user_service.py

Which file should contain the function to fetch user data from the database?

medium

A. routes/user.py

B. models/user.py

C. services/user_service.py

D. app/__init__.py

Solution

1. Step 1: Understand folder responsibilities

   routes handles API endpoints, models defines data structures, and services contains business logic like fetching data.

2. Step 2: Match function purpose to folder

   Fetching user data is business logic, so it belongs in services/user_service.py.

3. Final Answer:

   services/user_service.py -> Option C

4. Quick Check:

   Data fetching logic goes in services [OK]

Hint: Business logic like fetching data belongs in services [OK]

Common Mistakes:

• Putting fetching logic in routes
• Adding functions to models instead of services
• Using __init__.py for logic

4. You see this folder structure in a FastAPI project:

app/
  routes.py
  models.py
  services.py
  database.py

What is a likely problem with this structure as the project grows?

medium

A. Too many files in root, making it hard to maintain

B. Using .py files instead of folders is invalid in FastAPI

C. Missing a templates folder for HTML rendering

D. Database code should be inside routes.py

Solution

1. Step 1: Analyze flat file structure

   Having all files directly under app/ is okay for small projects but becomes cluttered and hard to maintain as code grows.

2. Step 2: Understand folder benefits

   Using folders like routes/, models/, and services/ helps organize code by purpose and improves maintainability.

3. Final Answer:

   Too many files in root, making it hard to maintain -> Option A

4. Quick Check:

   Flat structure hurts maintainability [OK]

Hint: Avoid many files in root; use folders for organization [OK]

Common Mistakes:

• Thinking .py files can't be used
• Confusing database code location
• Assuming templates folder is mandatory

5. You want to organize a FastAPI project that has multiple features like users, products, and orders. Which folder structure pattern best supports scalability and maintainability?

hard

A. Mix routes and models in the same folder to reduce folder count

B. Create separate folders for each feature with their own routes, models, and services inside

C. Keep all code files in the root folder for easy access

D. Put all routes in one routes folder, all models in one models folder, and all services in one services folder

Solution

1. Step 1: Understand feature-based folder structure

   Organizing by feature means each feature (users, products, orders) has its own folder containing routes, models, and services, improving modularity.

2. Step 2: Compare with other patterns

   Grouping all routes or models together can become large and hard to maintain. Keeping all files in root or mixing unrelated code reduces clarity.

3. Final Answer:

   Create separate folders for each feature with their own routes, models, and services inside -> Option B

4. Quick Check:

   Feature-based folders improve scalability [OK]

Hint: Use feature folders with routes, models, services inside [OK]

Common Mistakes:

• Using flat folders for all code
• Mixing unrelated code in one folder
• Ignoring modular design for growth