CRUD Operations

🗃️ Django Database Operations: CRUD Made Simple

The Story of the Magical Library 📚

Imagine you’re running a magical library. Every day, people come in to:

• Add new books to the shelves (Create)
• Find books they want to read (Read)
• Change book information like fixing a typo (Update)
• Remove old books nobody wants (Delete)

This is exactly what CRUD means! It’s the four things you do with data in any database.

🎯 What You’ll Master Today

✅ Basic CRUD Methods - The four magic spells
✅ Bulk Operations - Do many things at once
✅ Get or Create Patterns - Smart shortcuts

📖 Part 1: Basic CRUD Methods

The Four Magic Spells

Think of your database like a toy box. You can:

🆕 CREATE - Adding New Things

The Simplest Way:

# Method 1: Create and save separately
book = Book(title="Harry Potter", author="J.K. Rowling")
book.save()

# Method 2: Create and save together (easier!)
book = Book.objects.create(
    title="Harry Potter",
    author="J.K. Rowling"
)

What’s happening?

• Book(...) = Make a new book (but it’s not saved yet!)
• .save() = Put it in the database
• .create(...) = Make AND save in one step

🔍 READ - Finding Things

Get ONE specific thing:

# Find book with id=1
book = Book.objects.get(id=1)

# Find by name
book = Book.objects.get(title="Harry Potter")

Get MANY things:

# Get ALL books
all_books = Book.objects.all()

# Get books by one author
jk_books = Book.objects.filter(author="J.K. Rowling")

# Get first 5 books
first_five = Book.objects.all()[:5]

graph TD
    A["Want to find data?"] --> B{How many?}
    B -->|Just ONE| C["use .get"]
    B -->|MANY or ALL| D["use .filter or .all"]
    C --> E["Returns ONE object"]
    D --> F["Returns a list"]

✏️ UPDATE - Changing Things

Change ONE thing:

# Step 1: Find the book
book = Book.objects.get(id=1)

# Step 2: Change it
book.title = "Harry Potter and the Sorcerer's Stone"

# Step 3: Save the change
book.save()

Change MANY things at once:

# Make all books by "Unknown" have a new author
Book.objects.filter(author="Unknown").update(
    author="Anonymous"
)

🗑️ DELETE - Removing Things

Remove ONE thing:

# Find it first
book = Book.objects.get(id=1)

# Delete it
book.delete()

Remove MANY things:

# Delete all books by one author
Book.objects.filter(author="Old Author").delete()

# ⚠️ Be careful! This deletes ALL books!
Book.objects.all().delete()

📖 Part 2: Bulk Operations

Why Bulk Operations?

Imagine you have 1000 new books to add. You could:

❌ Slow Way: Add one book, wait, add another, wait… (1000 trips to database!)

✅ Fast Way: Put all 1000 books in a truck and deliver once!

🚀 bulk_create - Add Many at Once

# Create a list of books
new_books = [
    Book(title="Book 1", author="Author A"),
    Book(title="Book 2", author="Author B"),
    Book(title="Book 3", author="Author C"),
]

# Add all at once - ONE database trip!
Book.objects.bulk_create(new_books)

Pro tip: For huge lists, use batches:

Book.objects.bulk_create(new_books, batch_size=100)

⚡ bulk_update - Change Many at Once

# Get books to update
books = Book.objects.filter(author="Old Name")

# Change each one
for book in books:
    book.author = "New Name"

# Save all changes at once!
Book.objects.bulk_update(books, ['author'])

The ['author'] tells Django which fields changed.

📊 Bulk Operations Comparison

graph LR
    A["Need to save 1000 items"] --> B{Which method?}
    B -->|One by one| C["1000 database calls 🐌"]
    B -->|bulk_create| D["1 database call 🚀"]

📖 Part 3: Get or Create Patterns

The Smart Shortcut

Have you ever tried to add a friend who’s already in your contacts?

Django has a smart way to handle this:

• If it exists → just get it
• If it doesn’t exist → create it

🎯 get_or_create - The Basic Pattern

# Try to find or create an author
author, created = Author.objects.get_or_create(
    name="J.K. Rowling"
)

# 'created' tells you what happened
if created:
    print("New author added!")
else:
    print("Author already existed!")

What you get back:

• author = the object (new or existing)
• created = True (new) or False (already existed)

🛠️ Adding Extra Data

What if you find nothing and need to create with more info?

author, created = Author.objects.get_or_create(
    name="J.K. Rowling",
    defaults={
        "country": "UK",
        "birth_year": 1965
    }
)

How it works:

• Searches by name="J.K. Rowling"
• If not found: creates with name + all defaults
• defaults are ONLY used when creating

🔄 update_or_create - Create OR Update

Sometimes you want to:

• Create if not exists
• Update if it does exist

author, created = Author.objects.update_or_create(
    name="J.K. Rowling",
    defaults={
        "latest_book": "The Ickabog",
        "is_active": True
    }
)

The magic:

• Found? → Updates with defaults
• Not found? → Creates with defaults

🤔 Which Pattern to Use?

graph TD
    A["What do you need?"] --> B{Already exists?}
    B -->|Don't care, just get it| C["get_or_create"]
    B -->|Want to update it| D["update_or_create"]
    C --> E["Returns existing OR creates new"]
    D --> F["Creates new OR updates existing"]

🎉 Quick Summary

Your New Superpowers:

Basic CRUD:

• 🆕 .create() - Add new stuff
• 🔍 .get() / .filter() - Find stuff
• ✏️ .save() / .update() - Change stuff
• 🗑️ .delete() - Remove stuff

Bulk Operations:

• 🚀 bulk_create() - Add many fast
• ⚡ bulk_update() - Change many fast

Smart Patterns:

• 🎯 get_or_create() - Get or make new
• 🔄 update_or_create() - Get and update or make new

💡 Golden Rules

1. Use .create() instead of save() for new objects - it’s cleaner!

2. Use .get() when you expect exactly ONE result

   • It throws an error if 0 or 2+ results!

3. Use bulk operations for 10+ items - your database will thank you!

4. Use get_or_create to avoid duplicates - no more “already exists” errors!

🌟 Remember: Every app you use - Instagram, WhatsApp, games - they all do these same four things: Create, Read, Update, Delete. Now you know how too!