Gracefully handle list duplicate additions

bookwyrm/views/list.py

@@ -1,6 +1,7 @@
 ''' book list views'''
 from django.contrib.auth.decorators import login_required
 from django.core.paginator import Paginator
+from django.db import IntegrityError
 from django.db.models import Count, Q
 from django.http import HttpResponseNotFound, HttpResponseBadRequest
 from django.shortcuts import get_object_or_404, redirect
@@ -181,6 +182,7 @@ def add_book(request, list_id):
 
     book = get_object_or_404(models.Edition, id=request.POST.get('book'))
     # do you have permission to add to the list?
+    try:
         if request.user == book_list.user or book_list.curation == 'open':
             # go ahead and add it
             models.ListItem.objects.create(
@@ -199,6 +201,9 @@ def add_book(request, list_id):
         else:
             # you can't add to this list, what were you THINKING
             return HttpResponseBadRequest()
+    except IntegrityError:
+        # if the book is already on the list, don't flip out
+        pass
 
     return redirect('list', list_id)