Adding Custom Filters

Django allows you to create custom filters to add more complex filtering functionality in the admin panel.

1. Creating a Custom Filter: Suppose we want to filter books by the number of pages. We can create a custom filter like this:

   from django.contrib import admin
   from .models import Book
   
   class PagesFilter(admin.SimpleListFilter):
       title = 'Page Length'
       parameter_name = 'pages'
   
       def lookups(self, request, model_admin):
           return [
               ('short', 'Short'),
               ('long', 'Long'),
           ]
   
       def queryset(self, request, queryset):
           if self.value() == 'short':
               return queryset.filter(pages__lt=200)
           if self.value() == 'long':
               return queryset.filter(pages__gte=200)
           return queryset
   
   class BookAdmin(admin.ModelAdmin):
       list_filter = (PagesFilter,)
   
   admin.site.register(Book, BookAdmin)