for book in Book.objects.all():
source = book.extra_info.get('source_url', '')
if self.netloc in source or (old_netloc != self.netloc and old_netloc in source):
for book in Book.objects.all():
source = book.extra_info.get('source_url', '')
if self.netloc in source or (old_netloc != self.netloc and old_netloc in source):