show better error message when recipe deletion breaks due to constraints

cookbook/views/delete.py

@@ -1,7 +1,7 @@
 from django.contrib import messages
 from django.db.models import ProtectedError
 from django.http import HttpResponseRedirect
-from django.shortcuts import get_object_or_404
+from django.shortcuts import get_object_or_404, render
 from django.urls import reverse, reverse_lazy
 from django.utils.translation import gettext as _
 from django.views.generic import DeleteView
@@ -23,9 +23,31 @@ class RecipeDelete(GroupRequiredMixin, DeleteView):
     model = Recipe
     success_url = reverse_lazy('index')
 
+    def delete(self, request, *args, **kwargs):
+        obj = self.get_object()
+
+        related_objects = []
+        for x in obj._meta.get_fields():
+            try:
+                related = x.related_model.objects.filter(**{x.field.name: obj})
+                if related.exists():
+                    related_objects.append(related)
+            except AttributeError:
+                pass
+
+        if related_objects:
+            self.object = obj
+            return render(request, template_name=self.template_name, context=self.get_context_data(related_objects=related_objects))
+
+        success_url = self.get_success_url()
+        obj.delete()
+        return HttpResponseRedirect(success_url)
+
     def get_context_data(self, **kwargs):
         context = super(RecipeDelete, self).get_context_data(**kwargs)
         context['title'] = _("Recipe")
+        if 'related_objects' in kwargs:
+            context['related_objects'] = kwargs.pop('related_objects')
         return context