What are Django Models and how do you use the ORM for database operations? Django Models क्या हैं और ORM का use करके database operations कैसे करते हैं?

Django Models are Python classes that define database table structure. The ORM (Object-Relational Mapping) abstracts SQL, allowing you to interact with database using Python code instead of writing raw SQL queries.

// Define Models
from django.db import models
from django.contrib.auth.models import User

class Category(models.Model):
    name = models.CharField(max_length=100)
    description = models.TextField()
    created_at = models.DateTimeField(auto_now_add=True)
    
    class Meta:
        ordering = ['name']
        verbose_name_plural = 'Categories'
    
    def __str__(self):
        return self.name

class Product(models.Model):
    CATEGORY_CHOICES = [
        ('electronics', 'Electronics'),
        ('clothing', 'Clothing'),
        ('books', 'Books'),
    ]
    
    name = models.CharField(max_length=200)
    description = models.TextField()
    price = models.DecimalField(max_digits=10, decimal_places=2)
    category = models.ForeignKey(Category, on_delete=models.CASCADE, related_name='products')
    quantity = models.IntegerField(default=0)
    is_active = models.BooleanField(default=True)
    created_by = models.ForeignKey(User, on_delete=models.SET_NULL, null=True)
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)
    
    class Meta:
        ordering = ['-created_at']
        indexes = [
            models.Index(fields=['name', 'category']),
        ]
    
    def __str__(self):
        return self.name

// ORM Query Operations
from myapp.models import Product, Category

// CREATE
product = Product.objects.create(
    name='Laptop',
    price=999.99,
    category_id=1,
    quantity=50
)

// READ - Get single object
product = Product.objects.get(id=1)  # Raises DoesNotExist if not found
product = Product.objects.filter(name='Laptop').first()  # Returns None if not found

// READ - Get all objects
all_products = Product.objects.all()

// READ - Filter
active_products = Product.objects.filter(is_active=True)
expensive = Product.objects.filter(price__gte=1000)
cheap = Product.objects.filter(price__lt=100)

// READ - Complex queries
from django.db.models import Q
products = Product.objects.filter(
    Q(name__icontains='phone') | Q(name__icontains='tablet'),
    is_active=True
)

// UPDATE
product = Product.objects.get(id=1)
product.price = 1299.99
product.save()

// Bulk update
Product.objects.filter(category_id=1).update(price=F('price') * 1.1)

// DELETE
product.delete()
Product.objects.filter(quantity=0).delete()

// Aggregation
from django.db.models import Sum, Count, Avg

total_revenue = Product.objects.aggregate(Sum('price'))
product_count = Product.objects.count()
avg_price = Product.objects.aggregate(Avg('price'))

// Grouping
from django.db.models import Sum
category_stats = Product.objects.values('category').annotate(
    total_products=Count('id'),
    avg_price=Avg('price')
)

// Ordering
products_asc = Product.objects.order_by('name')
products_desc = Product.objects.order_by('-created_at')

// Slicing
first_10 = Product.objects.all()[:10]
page_2 = Product.objects.all()[10:20]

// Relationships
# Get products in a category
category = Category.objects.get(id=1)
category_products = category.products.all()

# Get category of a product
product = Product.objects.get(id=1)
category = product.category