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# blog/views.py — mixins and get_context_data customisation
from django.views.generic import ListView, DetailView
from django.contrib.auth.mixins import LoginRequiredMixin
from django.contrib import messages
from .models import Post, Tag

class SuccessMessageMixin:
    success_message = ''

def form_valid(self, form):
        response = super().form_valid(form)
        if self.success_message:
            messages.success(self.request, self.success_message)
        return response

class OwnerRequiredMixin:
    """Restrict edit/delete to the object owner."""
    def dispatch(self, request, *args, **kwargs):
        obj = self.get_object()
        if obj.author != request.user:
            from django.core.exceptions import PermissionDenied
            raise PermissionDenied
        return super().dispatch(request, *args, **kwargs)

class PostListView(ListView):
    model               = Post
    template_name       = 'blog/post_list.html'
    context_object_name = 'posts'
    paginate_by         = 10

def get_queryset(self):
        qs = Post.published.select_related('author')
        tag_slug = self.kwargs.get('tag_slug')
        if tag_slug:
            self.tag = Tag.objects.get(slug=tag_slug)
            qs = qs.filter(tags=self.tag)
        return qs.order_by('-published_at')

def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        context['all_tags']    = Tag.objects.all()
        context['active_tag']  = getattr(self, 'tag', None)
        context['total_posts'] = Post.published.count()
        return context

# blog/urls.py — as_view() usage
from django.urls import path
from . import views

urlpatterns = [
    path('', views.PostListView.as_view(), name='post-list'),
    path('tag/<slug:tag_slug>/', views.PostListView.as_view(), name='posts-by-tag'),
]