Day 5 : Real-World Parameter Integration in FastAPI (Path + Query + Body)

Welcome to Day 5 of the FastAPI Zero to Hero series!

Today we combine the three types of parameters you'll encounter in any real-world backend project:

• ✅ Path Parameters
• ✅ Query Parameters
• ✅ Body Parameters

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📌 Scenario: Update a User's Profile with Notifications

We’ll build an API where:

• The user is identified via Path
• Notification preference is passed via Query
• New profile data is passed in the Request Body

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🧱 Install or Activate Your FastAPI Environment

If you haven't yet:

pip install fastapi uvicorn

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🧪 Step-by-Step Code

📁 File: test.py

from fastapi import FastAPI, Path, Query, Body
from pydantic import BaseModel
from typing import Optional

app = FastAPI()

# Request Body Model
class UserUpdateRequest(BaseModel):
    name: str
    email: str
    age: Optional[int] = None

# Response Model
class UserResponse(BaseModel):
    id: int
    name: str
    notify: bool

@app.put("/user/{user_id}", response_model=UserResponse)
def update_user(
    user_id: int = Path(..., description="ID of the user to update"),
    notify: bool = Query(False, description="Whether to notify the user"),
    user: UserUpdateRequest = Body(...)
):
    # Simulate logic: update user in DB, send notification, etc.
    print(f"Updating user {user_id}: {user.dict()}")
    if notify:
        print(f"Sending notification to {user.email}...")

    return UserResponse(
        id=user_id,
        name=user.name,
        notify=notify
    )

🚀 Test Your Endpoint

✅ 1. Run the Server

Make sure your test.py file is saved, then run it using Uvicorn:

uvicorn test:app --host 0.0.0.0 --reload --port 9002

🧪 2. Use Swagger UI (Recommended for Beginners)

FastAPI comes with auto-generated interactive API documentation via Swagger UI.

🧭 Steps to Test:

1. Open your browser.
2. Navigate to: http://localhost:9002/docs
3. Locate the PUT /user/{user_id} endpoint.
4. Click on it → then click "Try it out".
5. Fill in the fields:

• user_id: 123
• notify: true
• JSON Body:

 {
       "name": "Utkarsh",
       "email": "[e-mail]",
       "age": 30
     }

1. Click Execute.

✅ You will see:

• The full request URL
• The response status
• The returned JSON result

It's a great way to explore and test your API without writing any client code!

Output:

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🧠 What You Just Did

Here's a breakdown of how different FastAPI components worked together in your endpoint:

Part	What it Does
Path	Identifies the user by user_id
Query	Controls logic flow (e.g., whether to notify)
Body	Sends structured profile update data (JSON)
Response	Filters output using response_model to limit what gets returned

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🧰 Bonus: Add Validation to Your Parameters

You can enhance your endpoint by adding validation rules to the Path and Query parameters:

user_id: int = Path(..., gt=0, description="User ID must be positive"),
notify: bool = Query(False, description="Notify user after update"),

• gt=0 ensures the user_id is a positive integer.
• description improves the auto-generated API documentation by adding helpful context to parameters.

🧪 Explore Your API at /docs

Run your server if it’s not running already:

uvicorn test:app --host 0.0.0.0 --reload --port 9002

Then, open your browser and navigate to:

📄 Swagger UI: http://localhost:9002/docs

You’ll see an auto-generated Swagger UI with:

• ✅ All your defined endpoints
• 🧩 Parameter descriptions
• 📦 Data models for request/response
• 🧪 Interactive testing interface

💡 This is one of the best features of FastAPI — instant, interactive API docs powered by your Python code and type hints!

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🧩 Wrap-Up

In real-world applications, API routes almost always require a mix of:

• ✅ Path parameters for routing (e.g., user ID)
• ✅ Query parameters for optional behavior (e.g., notify=true)
• ✅ Body data for resource creation or updates (e.g., profile info)

And now, you know how to combine and validate all three like a pro. 💪

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🙏 Credits

Huge thanks to the FastAPI Official Documentation by Sebastián Ramírez (@tiangolo) — the best place to learn and explore everything about FastAPI.

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👨‍💻 About Me

Hey there! I’m Utkarsh Rastogi, an AWS Community Builder and passionate cloud-native enthusiast who loves building scalable backend systems and sharing knowledge with the community.

🔗 Connect with me: Utkarsh Rastogi

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💬 Share Your Thoughts – I'd Love Your Feedback!

If you enjoyed today's post or learned something new, I'd truly appreciate it if you leave a comment or share your thoughts 👇

Your feedback, questions, or even a quick “🔥 Loved this!” keeps me motivated to continue this journey and share more in the upcoming #FastAPIDaily posts.

✅ What did you find most helpful?

✅ Anything you'd like explained in the next part?

✅ Suggestions for improvement? I’m all ears! 🙌

Let’s grow and learn together — one FastAPI day at a time 🚀

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