Folder structure patterns in FastAPI - Step-by-Step Execution

Concept Flow - Folder structure patterns

Start Project

↓

Create main.py

↓

Add folders: app/, tests/

↓

Inside app/: create subfolders

↓

app/api/ -> routes

↓

app/models/ -> data models

↓

app/schemas/ -> data validation

↓

app/core/ -> config, security

↓

app/db/ -> database connection

↓

tests/ -> test files

↓

Run FastAPI server

↓

Project organized and ready

This flow shows how a FastAPI project is organized step-by-step into folders for routes, models, schemas, core logic, database, and tests.

Execution Sample

FastAPI

app/
  api/
    v1.py
  models/
    user.py
  schemas/
    user.py
  core/
    config.py
  db/
    session.py
main.py

This folder structure organizes FastAPI code by responsibility: api for routes, models for data models, schemas for validation, core for config, db for database, and main.py to start the app.

Execution Table

Step	Action	Folder/File Created	Purpose	Notes
1	Create project root	project_root/	Base folder	Starting point
2	Create main app folder	app/	Holds app code	Main source folder
3	Create api folder	app/api/	Store route files	Organizes endpoints
4	Create models folder	app/models/	Define data models	Database models here
5	Create schemas folder	app/schemas/	Define data validation	Pydantic schemas
6	Create core folder	app/core/	Config and security	Settings and auth
7	Create db folder	app/db/	Database connection	Session and engine
8	Create tests folder	tests/	Test files	Separate from app code
9	Create main.py	main.py	Start FastAPI app	Entry point
10	Run server	N/A	Start app	App ready to serve requests
11	Exit	N/A	Setup complete	Project structured

💡 All folders and files created to organize FastAPI project logically.

Variable Tracker

Folder/File	Start	After Step 3	After Step 6	After Step 9	Final
project_root/	Not exist	Exists	Exists	Exists	Exists
app/	Not exist	Exists	Exists	Exists	Exists
app/api/	Not exist	Exists	Exists	Exists	Exists
app/models/	Not exist	Not exist	Exists	Exists	Exists
app/schemas/	Not exist	Not exist	Exists	Exists	Exists
app/core/	Not exist	Not exist	Exists	Exists	Exists
app/db/	Not exist	Not exist	Not exist	Exists	Exists
tests/	Not exist	Not exist	Not exist	Exists	Exists
main.py	Not exist	Not exist	Not exist	Exists	Exists

Key Moments - 3 Insights

Why do we separate 'models' and 'schemas' folders?

Models define how data is stored (database), schemas define how data is validated and sent over the network. See steps 4 and 5 in execution_table.

Why is 'tests' folder outside 'app' folder?

Tests are kept separate to avoid mixing test code with production code. This separation helps clarity and deployment. See step 8.

What is the role of 'main.py'?

'main.py' is the entry point that starts the FastAPI server. It imports routes and runs the app. See step 9.

Visual Quiz - 3 Questions

Look at the execution_table, at which step is the 'schemas' folder created?

A Step 3

B Step 5

C Step 7

D Step 9

💡 Hint

Check the 'Folder/File Created' column for 'app/schemas/' in execution_table rows.

According to variable_tracker, which folder appears last in the project structure?

A tests/

B app/db/

C app/api/

D app/core/

💡 Hint

Look at the final column in variable_tracker to see which folders exist at the end.

If we skip creating 'app/core/', what impact does it have on the project?

A No impact, core is optional

B Routes will not work

C Config and security code will have no dedicated place

D Database connection will fail

💡 Hint

Refer to step 6 in execution_table describing 'app/core/' purpose.

Concept Snapshot

FastAPI folder structure:
- app/: main code
- app/api/: routes
- app/models/: database models
- app/schemas/: data validation
- app/core/: config and security
- app/db/: database connection
- tests/: test files
- main.py: app entry point
Organize by responsibility for clarity and maintainability.

Full Transcript

This visual execution shows how to organize a FastAPI project by creating folders step-by-step. We start with the project root, then add the app folder. Inside app, we create api for routes, models for database models, schemas for data validation, core for configuration and security, and db for database connection. Separately, we create a tests folder for test code. Finally, main.py is created as the entry point to start the FastAPI server. This structure helps keep code organized and easy to maintain.

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