Django过滤器基于多个条件在order_by之后返回重复项

Question

I'm having difficulty returning unique Clazz objects based off my criteria and ordering. Clazz and Session are two separate models and a class can have many sessions.

Once I introduced the order_by I'm seeing duplicate Clazz objects. How can I remove the duplicates? A simple distinct() doesn't seem to work.

classes = Clazz.objects.filter(location=loc).distinct().order_by('session__start_date', 'session__end_date')

Answer 1

I guess you can do something like this:

classes = Clazz.objects.filter(location=loc).annotate(
        startdate=Max('session__start_date'),
        end_date=Max('session__end_date')
    ).order_by('startdate', 'end_date')

Answer 2

After @Alasdair's response, ended up just doing this:

dup_list = []
class_list = []
for c in classes:
    if c not in dup_list:
        dup_list.append(c)
        class_list.append(c)
classes = class_list