What are Django Views? Explain Function-Based Views (FBV) vs Class-Based Views (CBV). Django Views क्या हैं? Function-Based Views (FBV) vs Class-Based Views (CBV) explain करें।

Views are Python functions/classes that receive requests and return responses. FBV are simple functions for straightforward logic, while CBV use classes with methods for complex reusable logic. CBV provides inheritance, mixins, and built-in HTTP method handling.

// FUNCTION-BASED VIEWS (FBV)
from django.shortcuts import render, redirect
from django.http import JsonResponse
from django.views.decorators.http import require_http_methods
from .models import Product
from .forms import ProductForm

# Simple view
@require_http_methods(['GET', 'POST'])
def product_list(request):
    if request.method == 'POST':
        form = ProductForm(request.POST)
        if form.is_valid():
            form.save()
            return redirect('product_list')
    else:
        form = ProductForm()
    
    products = Product.objects.all()
    return render(request, 'products/list.html', {
        'products': products,
        'form': form
    })

# Detail view with URL parameter
def product_detail(request, product_id):
    try:
        product = Product.objects.get(id=product_id)
        return render(request, 'products/detail.html', {'product': product})
    except Product.DoesNotExist:
        return render(request, '404.html', status=404)

// CLASS-BASED VIEWS (CBV)
from django.views import View
from django.views.generic import ListView, DetailView, CreateView, UpdateView, DeleteView
from django.contrib.auth.mixins import LoginRequiredMixin
from django.urls import reverse_lazy

# Generic view for listing
class ProductListView(ListView):
    model = Product
    template_name = 'products/list.html'
    context_object_name = 'products'
    paginate_by = 10
    
    def get_queryset(self):
        return Product.objects.filter(is_active=True)
    
    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        context['total_products'] = self.get_queryset().count()
        return context

# Generic view for detail
class ProductDetailView(DetailView):
    model = Product
    template_name = 'products/detail.html'
    context_object_name = 'product'
    pk_url_kwarg = 'product_id'

# Generic view for creation
class ProductCreateView(LoginRequiredMixin, CreateView):
    model = Product
    form_class = ProductForm
    template_name = 'products/form.html'
    success_url = reverse_lazy('product_list')
    
    def form_valid(self, form):
        form.instance.created_by = self.request.user
        return super().form_valid(form)

# Generic view for update
class ProductUpdateView(UpdateView):
    model = Product
    form_class = ProductForm
    template_name = 'products/form.html'
    pk_url_kwarg = 'product_id'
    
    def get_success_url(self):
        return reverse('product_detail', args=[self.object.id])

// Custom Class-Based View
class ProductAPIView(View):
    def get(self, request, product_id=None):
        if product_id:
            product = Product.objects.get(id=product_id)
            return JsonResponse({
                'id': product.id,
                'name': product.name,
                'price': str(product.price)
            })
        else:
            products = list(Product.objects.values('id', 'name', 'price'))
            return JsonResponse({'products': products})
    
    def post(self, request):
        # Handle POST
        data = request.POST
        product = Product.objects.create(**data)
        return JsonResponse({'id': product.id})

// urls.py
from django.urls import path
from . import views

urlpatterns = [
    # FBV routes
    path('products/', views.product_list, name='product_list'),
    path('products/<int:product_id>/', views.product_detail, name='product_detail'),
    
    # CBV routes
    path('api/products/', views.ProductListView.as_view(), name='product_list_cbv'),
    path('api/products/<int:pk>/', views.ProductDetailView.as_view(), name='product_detail_cbv'),
    path('api/products/create/', views.ProductCreateView.as_view(), name='product_create'),
]

// FBV vs CBV Comparison
// FBV Advantages:
// - Simple and straightforward
// - Direct control over logic
// - Easy for small views
// - Good for beginners

// CBV Advantages:
// - Reusable code
// - Inheritance and mixins
// - DRY principle
// - Built-in generic views
// - HTTP method separation
// - Better for complex applications