Personal Catalogue: Django & PostgreSQL — Chapter 6, Exercise 1
====================================================

TASK
Add the tag-filtering logic to ItemListView, make tags clickable in
the list template, and confirm visiting /?tag=python shows only items
actually tagged Python.

SOLUTION

1. catalogue/views.py — update ItemListView with the get_queryset() and
   get_context_data() overrides from the chapter:

    class ItemListView(ListView):
        model = Item
        template_name = 'catalogue/item_list.html'
        context_object_name = 'items'
        paginate_by = 25

        def get_queryset(self):
            queryset = Item.objects.select_related('item_type').prefetch_related('tags')
            tag_name = self.request.GET.get('tag')
            if tag_name:
                queryset = queryset.filter(tags__name=tag_name)
            return queryset

        def get_context_data(self, **kwargs):
            context = super().get_context_data(**kwargs)
            context['active_tag'] = self.request.GET.get('tag', '')
            return context

2. catalogue/templates/catalogue/item_list.html — inside the item loop,
   render each tag as a link:

    {% for tag in item.tags.all %}
      <a href="?tag={{ tag.name }}">#{{ tag.name }}</a>
    {% endfor %}

   And above the list, show the active filter with a way to clear it:

    {% if active_tag %}
      <p>Filtered by: #{{ active_tag }} <a href="{% url 'item_list' %}">(clear)</a></p>
    {% endif %}

CONFIRMING IT WORKS

Ensure at least one real item (from earlier chapters) is tagged
"Python", then visit the root URL with the query string /?tag=python
directly, or click a rendered "#Python" link from an item that carries
it. The list should now show only items actually tagged Python, with
the "Filtered by: #Python (clear)" banner visible, and clicking
"(clear)" should return to the full, unfiltered list.

WHY THIS WORKS AS AN ANSWER
----------------------------
It implements the filtering exactly as specified (reading the query
parameter, filtering via the ORM's own tags__name lookup), and verifies
the result both by direct URL and by using the clickable link the
template itself now produces, confirming the whole loop works end to
end.