在Django中为eauction toy-app处理并发的最佳方法

I am implementing an eauction toy-app in Django and am confused on how to best handle concurrency in the code below. I am uncertain which of my solution candidates (or any other) fits best with the design of Django. I am fairly new to Django/python and my SQL know-how is rusty so apologies if this is a no-brainer.I am implementing an eauction toy-app in Django