FastAPI_STATIONARY_STORE_COMPLETE-1.md

FastAPI CRUD - Stationary Store (In-Memory Database)

Complete Setup Guide - From Opening VS Code to Running Your API

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TABLE OF CONTENTS

1. Prerequisites
2. Phase 1: Environment Setup
3. Phase 2: Create Project Files
4. Phase 3: Run Your API
5. Phase 4: Test Everything
6. Troubleshooting

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PREREQUISITES

Before starting:

• ✅ Python 3.8+ installed
• ✅ VS Code installed
• ✅ A folder on Desktop called fastapi

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PHASE 1: ENVIRONMENT SETUP

STEP 1: Open VS Code

1. Click VS Code icon
2. VS Code opens

✅ Expected: VS Code window is open

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STEP 2: Open Your Project Folder

1. File → Open Folder
2. Navigate to Desktop
3. Select folder: fastapi
4. Click "Select Folder"

✅ Expected: Left sidebar shows "FASTAPI" folder (empty)

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STEP 3: Open Terminal

1. Terminal menu → New Terminal
2. Black/gray box appears at bottom

✅ Expected:

C:\Users\YourName\Desktop\fastapi>

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STEP 4: Switch to Command Prompt

PowerShell has issues. Use Command Prompt instead.

1. Click dropdown arrow next to + in terminal
2. Select "Command Prompt"
3. Close PowerShell tab (X button)

✅ Expected:

C:\Users\...\fastapi>

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STEP 5: Create Virtual Environment

Type:

python -m venv fastapi

Wait 30 seconds (nothing shows - normal!)

✅ Expected: Prompt returns

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STEP 6: Activate Virtual Environment

Type:

fastapi\Scripts\activate

✅ Expected:

(fastapi) C:\Users\...\fastapi>

Notice (fastapi) at start = activated! ✨

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STEP 7: Install FastAPI & Uvicorn

Type:

pip install fastapi uvicorn

Wait 1-2 minutes

✅ Expected:

Successfully installed fastapi-0.x.x uvicorn-0.x.x ...

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PHASE 2: CREATE PROJECT FILES

STEP 8: Create models.py

What: Blueprint for Products

In Explorer:

1. Right-click empty space
2. New File
3. Type: models.py
4. Press Enter

Copy and Paste this code:

from pydantic import BaseModel

class Product(BaseModel):
    id: int
    name: str
    desc: str
    price: int
    quantity: int

Explanation:

• id: int = Product ID (unique number)
• name: str = Product name (text)
• desc: str = Description (text)
• price: int = Price in rupees (number)
• quantity: int = Stock quantity (number)

Save: Ctrl + S

✅ Expected: No red errors

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STEP 9: Create main.py (THE MAIN FILE!)

What: All your API endpoints (routes)

In Explorer:

1. Right-click empty space
2. New File
3. Type: main.py
4. Press Enter

Copy and Paste ENTIRE code below:

from fastapi import FastAPI
from models import Product

app = FastAPI()

# ========================================
# IN-MEMORY DATABASE (LIST)
# Data stored in RAM - resets when server stops
# ========================================

products_db = [
    Product(id=1, name="Notebook A4", desc="100 pages ruled notebook", price=150, quantity=50),
    Product(id=2, name="Pen Set", desc="Pack of 10 quality pens", price=300, quantity=30),
    Product(id=3, name="Pencil Set", desc="12 HB pencils", price=120, quantity=40),
    Product(id=4, name="Highlighters", desc="5 neon color highlighters", price=250, quantity=25),
    Product(id=5, name="Eraser", desc="Rubber erasers (pack of 5)", price=80, quantity=100),
]

# ========================================
# ROOT ENDPOINT
# ========================================

@app.get("/")
def home():
    """
    GET / endpoint
    Returns welcome message
    """
    return {
        "message": "Welcome to Stationary Store API!",
        "total_products": len(products_db)
    }

# ========================================
# CREATE - Add new product
# ========================================

@app.post("/products/")
def create_product(product: Product):
    """
    POST /products/ endpoint
    Add new product to database
    Input: Product object (id, name, desc, price, quantity)
    Output: Confirmation message
    """
    # Check if product with this ID already exists
    for p in products_db:
        if p.id == product.id:
            return {"error": f"Product with id={product.id} already exists"}
    
    # Add new product
    products_db.append(product)
    return {
        "message": "Product created successfully",
        "product": product,
        "total_products": len(products_db)
    }

# ========================================
# READ - Get all products
# ========================================

@app.get("/products/")
def get_all_products():
    """
    GET /products/ endpoint
    Returns all products from database
    """
    return {
        "total": len(products_db),
        "products": products_db
    }

# ========================================
# READ - Get one product by ID
# ========================================

@app.get("/products/{product_id}")
def get_product(product_id: int):
    """
    GET /products/{product_id} endpoint
    Returns single product by ID
    Example: /products/1 → returns product with id=1
    """
    for product in products_db:
        if product.id == product_id:
            return {
                "found": True,
                "product": product
            }
    
    return {
        "found": False,
        "error": f"Product with id={product_id} not found"
    }

# ========================================
# UPDATE - Modify existing product
# ========================================

@app.put("/products/{product_id}")
def update_product(product_id: int, product: Product):
    """
    PUT /products/{product_id} endpoint
    Update existing product (replace all fields)
    """
    for i in range(len(products_db)):
        if products_db[i].id == product_id:
            products_db[i] = product
            return {
                "message": "Product updated successfully",
                "product": product
            }
    
    return {
        "error": f"Product with id={product_id} not found"
    }

# ========================================
# DELETE - Remove product
# ========================================

@app.delete("/products/{product_id}")
def delete_product(product_id: int):
    """
    DELETE /products/{product_id} endpoint
    Remove product from database
    """
    global products_db
    initial_count = len(products_db)
    products_db = [p for p in products_db if p.id != product_id]
    
    if len(products_db) < initial_count:
        return {
            "message": f"Product with id={product_id} deleted successfully",
            "remaining_products": len(products_db)
        }
    else:
        return {
            "error": f"Product with id={product_id} not found"
        }

# ========================================
# BONUS - Filter by price range
# ========================================

@app.get("/products/price-range/{min_price}/{max_price}")
def get_products_by_price(min_price: int, max_price: int):
    """
    GET /products/price-range/{min_price}/{max_price} endpoint
    Find products within price range
    Example: /products/price-range/100/200 → products between 100-200 rupees
    """
    filtered = [p for p in products_db if min_price <= p.price <= max_price]
    return {
        "price_range": f"{min_price}-{max_price}",
        "count": len(filtered),
        "products": filtered
    }

# ========================================
# BONUS - Find low stock products
# ========================================

@app.get("/products/low-stock/{threshold}")
def get_low_stock(threshold: int):
    """
    GET /products/low-stock/{threshold} endpoint
    Find products with quantity below threshold
    Example: /products/low-stock/30 → products with less than 30 in stock
    """
    low_stock = [p for p in products_db if p.quantity < threshold]
    return {
        "threshold": threshold,
        "count": len(low_stock),
        "products": low_stock
    }

Key Points:

• In-memory database = products_db = [...] (list in RAM)
• 5 Stationary Products pre-loaded:
  1. Notebook A4 - 150 rupees - 50 qty
  2. Pen Set - 300 rupees - 30 qty
  3. Pencil Set - 120 rupees - 40 qty
  4. Highlighters - 250 rupees - 25 qty
  5. Eraser - 80 rupees - 100 qty
• 8 Endpoints (routes): GET, POST, PUT, DELETE + 2 bonus filters

Save: Ctrl + S

✅ Expected: No red errors

---

---

PHASE 3: RUN YOUR API

STEP 10: Start the Server

In terminal (with (fastapi) showing)

Type:

uvicorn main:app --reload

Wait 3-5 seconds

✅ Expected:

INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO:     Application startup complete

Keep terminal open - server runs here!

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STEP 11: Open Documentation

Open your browser

Visit:

http://127.0.0.1:8000/docs

✅ Expected:

• Swagger UI page loads
• All 8 endpoints visible:
  • GET /
  • POST /products/
  • GET /products/
  • GET /products/{product_id}
  • PUT /products/{product_id}
  • DELETE /products/{product_id}
  • GET /products/price-range/{min_price}/{max_price}
  • GET /products/low-stock/{threshold}

---

---

PHASE 4: TEST EVERYTHING

TEST 1: Get Root Message (GET /)

1. Click endpoint GET /
2. Click "Try it out"
3. Click "Execute"

✅ Response:

{
  "message": "Welcome to Stationary Store API!",
  "total_products": 5
}

---

TEST 2: Get All Products (GET /products/)

1. Click GET /products/
2. Click "Try it out"
3. Click "Execute"

✅ Response:

{
  "total": 5,
  "products": [
    {
      "id": 1,
      "name": "Notebook A4",
      "desc": "100 pages ruled notebook",
      "price": 150,
      "quantity": 50
    },
    {
      "id": 2,
      "name": "Pen Set",
      "desc": "Pack of 10 quality pens",
      "price": 300,
      "quantity": 30
    },
    {
      "id": 3,
      "name": "Pencil Set",
      "desc": "12 HB pencils",
      "price": 120,
      "quantity": 40
    },
    {
      "id": 4,
      "name": "Highlighters",
      "desc": "5 neon color highlighters",
      "price": 250,
      "quantity": 25
    },
    {
      "id": 5,
      "name": "Eraser",
      "desc": "Rubber erasers (pack of 5)",
      "price": 80,
      "quantity": 100
    }
  ]
}

✅ What this means: All 5 stationary products loaded!

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TEST 3: Get One Product (GET /products/{product_id})

1. Click GET /products/{product_id}
2. Click "Try it out"
3. In field product_id, type: 2
4. Click "Execute"

✅ Response:

{
  "found": true,
  "product": {
    "id": 2,
    "name": "Pen Set",
    "desc": "Pack of 10 quality pens",
    "price": 300,
    "quantity": 30
  }
}

✅ What this means: Found Pen Set (id=2)!

---

TEST 4: Create New Product (POST /products/)

1. Click POST /products/
2. Click "Try it out"
3. In Request body, paste:

{
  "id": 6,
  "name": "Calculator",
  "desc": "Scientific calculator with 240 functions",
  "price": 499,
  "quantity": 15
}

4. Click "Execute"

✅ Response:

{
  "message": "Product created successfully",
  "product": {
    "id": 6,
    "name": "Calculator",
    "desc": "Scientific calculator with 240 functions",
    "price": 499,
    "quantity": 15
  },
  "total_products": 6
}

✅ What this means: New product added! Now 6 total.

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TEST 5: Verify New Product Was Added

1. Click GET /products/
2. Click "Try it out"
3. Click "Execute"

✅ Response includes all 6 products (original 5 + Calculator)

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TEST 6: Update a Product (PUT /products/{product_id})

Let's update product #1 (Notebook A4)

1. Click PUT /products/{product_id}
2. Click "Try it out"
3. In field product_id, type: 1
4. In Request body, paste:

{
  "id": 1,
  "name": "Notebook A4 Premium",
  "desc": "200 pages premium ruled notebook",
  "price": 200,
  "quantity": 45
}

5. Click "Execute"

✅ Response:

{
  "message": "Product updated successfully",
  "product": {
    "id": 1,
    "name": "Notebook A4 Premium",
    "desc": "200 pages premium ruled notebook",
    "price": 200,
    "quantity": 45
  }
}

✅ What this means: Notebook updated with new name, price, and quantity!

---

TEST 7: Delete a Product (DELETE /products/{product_id})

Let's delete product #3 (Pencil Set)

1. Click DELETE /products/{product_id}
2. Click "Try it out"
3. In field product_id, type: 3
4. Click "Execute"

✅ Response:

{
  "message": "Product with id=3 deleted successfully",
  "remaining_products": 5
}

✅ What this means: Pencil Set deleted! Only 5 products left.

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TEST 8: Verify Deletion

1. Click GET /products/
2. Click "Try it out"
3. Click "Execute"

✅ Response: Only 5 products (Pencil Set is gone!)

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TEST 9: Try to Get Deleted Product

1. Click GET /products/{product_id}
2. Click "Try it out"
3. In field product_id, type: 3
4. Click "Execute"

✅ Response:

{
  "found": false,
  "error": "Product with id=3 not found"
}

✅ What this means: Confirms deletion worked!

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TEST 10: Filter by Price Range (GET /products/price-range/{min_price}/{max_price})

Find products between 100-200 rupees

1. Click GET /products/price-range/{min_price}/{max_price}
2. Click "Try it out"
3. In field min_price, type: 100
4. In field max_price, type: 200
5. Click "Execute"

✅ Response: Products in 100-200 range

{
  "price_range": "100-200",
  "count": 2,
  "products": [
    {
      "id": 1,
      "name": "Notebook A4 Premium",
      "price": 200,
      "quantity": 45
    },
    {
      "id": 3,
      "name": "Pencil Set",
      "price": 120,
      "quantity": 40
    }
  ]
}

---

TEST 11: Find Low Stock Products (GET /products/low-stock/{threshold})

Find products with less than 30 in stock

1. Click GET /products/low-stock/{threshold}
2. Click "Try it out"
3. In field threshold, type: 30
4. Click "Execute"

✅ Response: Products with quantity < 30

{
  "threshold": 30,
  "count": 2,
  "products": [
    {
      "id": 4,
      "name": "Highlighters",
      "quantity": 25
    },
    {
      "id": 5,
      "name": "Eraser",
      "quantity": 100
    }
  ]
}

---

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STOPPING AND RESTARTING

How to Stop

In terminal with server running:

Press Ctrl + C

✅ Result: Server stops

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How to Restart Next Time

Every time you work on project:

fastapi\Scripts\activate

Then:

uvicorn main:app --reload

Then visit: http://127.0.0.1:8000/docs

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YOUR PROJECT STRUCTURE

After completing:

fastapi/
├── models.py              ← Product blueprint
├── main.py               ← API with 8 endpoints
├── fastapi/              ← Virtual environment
│   ├── Scripts/
│   ├── Lib/
│   └── ...
├── pyvenv.cfg
└── .gitignore

---

IN-MEMORY DATABASE EXPLANATION

What you're using:

products_db = [
    Product(id=1, name="Notebook A4", ...),
    Product(id=2, name="Pen Set", ...),
    # ... more products
]

Advantages:

• ✅ Super fast (data in RAM)
• ✅ Simple to understand
• ✅ Perfect for learning

Disadvantages:

• ❌ Data lost when server stops
• ❌ Not for production
• ❌ Only works on one server

Future: Replace with SQLite or PostgreSQL for permanent storage

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WHAT YOU'VE LEARNED

Concept	What It Is
Virtual Environment	Isolated Python space
FastAPI	Web framework for APIs
Uvicorn	Server that runs your API
Pydantic Models	Data blueprints (Product class)
Routes/Endpoints	URLs that do different things
@app.get()	GET endpoint (retrieve data)
@app.post()	POST endpoint (add data)
@app.put()	PUT endpoint (update data)
@app.delete()	DELETE endpoint (remove data)
CRUD	Create, Read, Update, Delete
In-Memory DB	Data storage in RAM
Swagger UI	Interactive API documentation

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TROUBLESHOOTING

Problem	Solution
Scripts\activate not found	Run python -m venv fastapi first
ModuleNotFoundError: fastapi	Make sure venv activated (shows (fastapi)), then pip install fastapi uvicorn
The system cannot find the path	Use Command Prompt, not PowerShell
Can't import models	Make sure models.py in same folder as main.py
Port 8000 already in use	Run: uvicorn main:app --port 8001 --reload
Swagger UI blank	Refresh browser (Ctrl+R). Check terminal for errors.
Changes not showing	Save Python file (Ctrl+S). Server auto-restarts with --reload.
Tried to create product with same ID	Error message appears: "Product with id=X already exists"

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CHECKLIST - Complete All

Environment Setup

• Python installed
• VS Code installed
• fastapi folder on Desktop
• Virtual environment created
• Virtual environment activated (shows (fastapi))
• FastAPI + Uvicorn installed

Files Created

• models.py created (Product class)
• main.py created (all endpoints)
• Both files saved

Server Running

• Terminal shows Uvicorn running on http://127.0.0.1:8000
• Browser shows Swagger UI at http://127.0.0.1:8000/docs

Tests Passing

• TEST 1: GET / works
• TEST 2: GET /products/ shows 5 products
• TEST 3: GET /products/2 returns Pen Set
• TEST 4: POST /products/ creates Calculator
• TEST 5: Verify new product in list (6 total)
• TEST 6: PUT /products/1 updates Notebook
• TEST 7: DELETE /products/3 deletes Pencil Set
• TEST 8: Verify product deleted
• TEST 9: GET deleted product returns error
• TEST 10: Price range filter works
• TEST 11: Low stock filter works

Ready for Next Phase

• All tests passing
• Server stops/starts correctly
• Understanding CRUD operations
• Code backup made

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STATIONARY PRODUCTS IN YOUR API

ID	Product	Price	Stock
1	Notebook A4	₹150	50
2	Pen Set	₹300	30
3	Pencil Set	₹120	40
4	Highlighters	₹250	25
5	Eraser	₹80	100

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NEXT PHASES (When Ready)

1. Add Real Database → SQLite, PostgreSQL, MongoDB
2. Add Validation → Check prices, quantities
3. Add Authentication → User login system
4. Add Categories → Group products by type
5. Deploy to Cloud → Make public (Heroku, Railway)