made generate_directory use atomic transactions. this increases performance significantly on unviewed directories.

comic/util.py

@@ -1,6 +1,7 @@
 from collections import OrderedDict
 from os import path, listdir
 
+from django.db.transaction import atomic
 from django.utils.http import urlsafe_base64_encode
 
 from .models import ComicBook, Setting, ComicStatus, Directory
@@ -105,6 +106,7 @@ def generate_directory(user, directory=False):
     else:
         dir_path = ''
         ordered_dir_list = get_ordered_dir_list(base_dir)
+    with atomic():
         for file_name in ordered_dir_list:
             df = DirFile()
             df.name = file_name