Creating a Basic FastAPI Application with CRUD Operations

Sakshi Agarwal — Thu, 13 Nov 2025 12:13:55 +0000

FastAPI is one of the fastest-growing Python frameworks for building modern APIs. It is fast, easy to use, and comes with built-in data validation using Pydantic.

🚀 What We Will Build
A simple API that manages Items with the following fields:

id
name
description
price
in_stock

We will implement:

Create an item
Read all items / single item
Update an item
Delete an item

📦 Project Setup

Ensure you have Python 3.8+ installed.

Install FastAPI & Uvicorn

pip install fastapi uvicorn

🗂️ Project Structure

fastapi-crud/
│
├── main.py
└── models.py

🧱 Step 1: Create the Pydantic Model (models.py)

from pydantic import BaseModel


class Item(BaseModel):
    id: int
    name: str
    description: str | None = None
    price: float
    in_stock: bool = True

⚙️ Step 2: Build FastAPI CRUD Endpoints (main.py)

from fastapi import FastAPI, HTTPException
from models import Item


app = FastAPI()


# Temporary in-memory database
items_db = {}


# Create an Item
@app.post("/items", status_code=201)
def create_item(item: Item):
    if item.id in items_db:
        raise HTTPException(status_code=400, detail="Item already exists")
        items_db[item.id] = item
    return {"message": "Item created successfully", "item": item}


# Read All Items
@app.get("/items")
def get_items():
    return list(items_db.values())


# Read Single Item
@app.get("/items/{item_id}")
def get_item(item_id: int):
    if item_id not in items_db:
        raise HTTPException(status_code=404, detail="Item not found")
    return items_db[item_id]


# Update Item
@app.put("/items/{item_id}")
def update_item(item_id: int, item: Item):
    if item_id not in items_db:
        raise HTTPException(status_code=404, detail="Item not found")
    items_db[item_id] = item
    return {"message": "Item updated", "item": item}


# Delete Item
@app.delete("/items/{item_id}")
def delete_item(item_id: int):
    if item_id not in items_db:
        raise HTTPException(status_code=404, detail="Item not found")
    del items_db[item_id]
    return {"message": "Item deleted"}

▶️ Step 3: Run the Application

uvicorn main:app --reload

API will be available at:

http://127.0.0.1:8000

🧪 Step 4: Test Using Swagger UI

FastAPI automatically provides beautiful interactive API docs.

Open:

http://127.0.0.1:8000/docs

You can test all CRUD operations directly there.

🎯 Summary

We learned how to build a clean FastAPI application with:

Pydantic models
CRUD Routes
In-memory storage
Automatic interactive API documentatio n

DEV Community: Sakshi Agarwal

Creating a Basic FastAPI Application with CRUD Operations