How to get the difference of two querysets in Django?

Question

I have to querysets. alllists and subscriptionlists

alllists = List.objects.filter(datamode = \'A\')
subscriptionlists = Membership.objects.filter(member__id         


        

Answer 1

How about:

subscriptionlists = Membership.objects.filter(member__id=memberid, datamode='A')
unsubscriptionlists = Membership.objects.exclude(member__id=memberid, datamode='A')

The unsubscriptionlists should be the inverse of subscription lists.

Brian's answer will work as well, though set() will most likely evaluate the query and will take a performance hit in evaluating both sets into memory. This method will keep the lazy initialization until you need the data.

Answer 2

You should be able to use the set operation difference to help:

set(alllists).difference(set(subscriptionlists))

Answer 3

Well I see two options here.

1. Filter things manually (quite ugly)

diff = []
for all in alllists:
    found = False
    for sub in subscriptionlists:
        if sub.id == all.id:
            found = True 
            break
    if not found:
        diff.append(all)

2. Just make another query

diff = List.objects.filter(datamode = 'A').exclude(member__id=memberid, datamode='A')

Answer 4

Since Django 1.11, QuerySets have a difference() method amongst other new methods:

# Capture elements that are in qs_all but not in qs_part
qs_diff = qs_all.difference(qs_part)    

Also see: https://stackoverflow.com/a/45651267/5497962