old_contents: from django.contrib import admin
  from django.db.models import F
  
  from resources.models import Resource, ResourceSubmission, ResourceVerification
  
  
  class ResourceAdmin(admin.ModelAdmin):
      search_fields = ('url',)
  
  admin.site.register(Resource, ResourceAdmin)
  admin.site.register(ResourceSubmission)
  
  
  class UnreachableResourceFilter(admin.SimpleListFilter):
      title = 'unreachable resource'
      parameter_name = 'unreachable'
  
      def lookups(self, request, model_admin):
          return (
              ('unreachable', 'all unreachable'),
          )
  
      def queryset(self, request, queryset):
          if self.value():  # must be 'unreachable', since that's the only lookup option
              return queryset.exclude(last_success__gt=F('last_failure'))
          else:
              return queryset
  
  
  class ResourceVerificationAdmin(admin.ModelAdmin):
      list_filter = (UnreachableResourceFilter,)
  
  admin.site.register(ResourceVerification, ResourceVerificationAdmin)
  
new_contents: from django.contrib import admin
  from django.db.models import F
  
  from resources.models import Resource, ResourceSubmission, ResourceVerification
  
  
  class ResourceAdmin(admin.ModelAdmin):
      search_fields = ('url',)
  
  admin.site.register(Resource, ResourceAdmin)
  
  
  class ResourceSubmissionAdmin(admin.ModelAdmin):
      search_fields = ('resource__url',)
  
  admin.site.register(ResourceSubmission, ResourceSubmissionAdmin)
  
  
  class UnreachableResourceFilter(admin.SimpleListFilter):
      title = 'unreachable resource'
      parameter_name = 'unreachable'
  
      def lookups(self, request, model_admin):
          return (
              ('unreachable', 'all unreachable'),
          )
  
      def queryset(self, request, queryset):
          if self.value():  # must be 'unreachable', since that's the only lookup option
              return queryset.exclude(last_success__gt=F('last_failure'))
          else:
              return queryset
  
  
  class ResourceVerificationAdmin(admin.ModelAdmin):
      search_fields = ('url',)
      list_filter = (UnreachableResourceFilter,)
  
  admin.site.register(ResourceVerification, ResourceVerificationAdmin)
  
subject: add url search for ResourceSubmission and ResourceVerification