Django Update Data

Modifying existing records in your database

✏️ What is Updating Data?

Updating data means modifying existing records in your database. Django provides multiple methods to update single or multiple records efficiently using model instances or querysets. 


# Update a product price
product = Product.objects.get(id=1)
product.price = 899.99
product.save()

Key Update Methods

🔄

Get & Save

Retrieve, modify, then save 

obj.field = value
obj.save()
⚡

Update Method

Update multiple records at once 

Model.objects.update()
🎯

Filter & Update

Update specific records 

Model.objects.filter().update()
🔀

Update or Create

Update if exists, create if not 

update_or_create()

🔹 Method 1: Get, Modify, and Save

Retrieve a single record, change its fields, and save it back to the database. This is the most straightforward method for updating individual records. 

# models.py
from django.db import models

class Product(models.Model):
    name = models.CharField(max_length=100)
    price = models.DecimalField(max_digits=10, decimal_places=2)
    stock = models.IntegerField()

# Get the product
product = Product.objects.get(id=1)

# Update fields
product.price = 899.99
product.stock = 45

# Save changes
product.save()

print(f"Updated {product.name}: ${product.price}, Stock: {product.stock}")

Output:

Updated Laptop: $899.99, Stock: 45

🔹 Method 2: Using update() Method

Update multiple records at once using the update() method on a queryset: 

# Update all products with stock less than 10
updated_count = Product.objects.filter(stock__lt=10).update(
    stock=100
)

print(f"Updated {updated_count} products")

Output:

Updated 5 products

⚠️ Important Note:

The update() method is faster but doesn't call save() method or send signals. Use it for bulk updates.

🔹 Update Specific Records

Use filters to update only records that match certain conditions: 

# Update products by category
Product.objects.filter(category='electronics').update(
    discount=10
)

# Update products with price greater than 500
Product.objects.filter(price__gt=500).update(
    shipping_free=True
)

# Update single product by name
Product.objects.filter(name='Laptop').update(
    price=799.99,
    stock=30
)

print("Products updated successfully")

Output:

Products updated successfully

🔹 Update with F() Expressions

Use F() to reference field values in updates: 

from django.db.models import F

# Increase all prices by 10%
Product.objects.all().update(
    price=F('price') * 1.10
)

# Decrease stock by 1 for all products
Product.objects.all().update(
    stock=F('stock') - 1
)

# Double the discount
Product.objects.filter(discount__gt=0).update(
    discount=F('discount') * 2
)

print("Prices and stock updated")

Output:

Prices and stock updated

🔹 Update or Create

Update a record if it exists, or create it if it doesn't: 

# Update or create product
product, created = Product.objects.update_or_create(
    name='Laptop',
    defaults={
        'price': 999.99,
        'stock': 50,
        'category': 'electronics'
    }
)

if created:
    print(f"Created new product: {product.name}")
else:
    print(f"Updated existing product: {product.name}")

Output (if updated):

Updated existing product: Laptop

🔹 Update from Forms

Update records from user input in views: 

# views.py
from django.shortcuts import render, redirect, get_object_or_404
from .models import Product

def edit_product(request, product_id):
    product = get_object_or_404(Product, id=product_id)
    
    if request.method == 'POST':
        # Get updated data from form
        product.name = request.POST.get('name')
        product.price = request.POST.get('price')
        product.stock = request.POST.get('stock')
        
        # Save changes
        product.save()
        
        return redirect('product_list')
    
    return render(request, 'edit_product.html', {'product': product})
<!-- templates/edit_product.html -->
<form method="post">
    {% csrf_token %}
    <input type="text" name="name" value="{{ product.name }}">
    <input type="number" name="price" step="0.01" value="{{ product.price }}">
    <input type="number" name="stock" value="{{ product.stock }}">
    <button type="submit">Update Product</button>
</form>

🔹 Partial Updates

Update only specific fields without affecting others: 

# Update only the price field
product = Product.objects.get(id=1)
product.price = 699.99
product.save(update_fields=['price'])

# Update multiple specific fields
product.price = 799.99
product.stock = 25
product.save(update_fields=['price', 'stock'])

print(f"Updated price and stock for {product.name}")

Output:

Updated price and stock for Laptop

🧠 Test Your Knowledge

Which method updates multiple records at once?