Django sum on query set

Question

I have a queryset in django with condition as follows:

query_set = MyModel.objects.annotate(TWWByRuns=(
    Case(
        When(Q(toss_winner=F('winner')) & Q(win_by_runs=0), then=1),
        output_field=FloatField(), default=0)
    )
).values('TWWByRuns')

I would like to use django built-in sum function to add whenever the value in the query_set equals to 1 as in when then=1. I know to use the sum function without conditionals but here since I have condition where should I use the sum function in this query_set?

score 3 · Accepted Answer · answered Jan 14 '19 at 11:14

3

In this specific case, it makes more sense to count:

MyModel.objects.filter(toss_winner=F('winner'), win_by_runs=0).count()

We here thus simply check how many MyModel records satisfy the given condition.

answered Jan 14 '19 at 11:14

Willem Van Onsem

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So this condition is similar to checking whether MyModel.toss_winner = MyModel.winner and MyModel.win_by_runs = 0? – Lax_Sam Jan 14 '19 at 11:19
@Laxman: yes. We thus count the number of `MyModel` records, for which that condition holds. – Willem Van Onsem Jan 14 '19 at 11:19
Ok. One last question. How to check not equal to in django? Because according to my understanding there is no '!=' operator in django. – Lax_Sam Jan 14 '19 at 11:21
To check win_by_runs != 0 what should be the operator? – Lax_Sam Jan 14 '19 at 11:22
@Laxman: you negate that part of the query, like `MyModel.objects.filter(toss_winner=F('winner'), ~Q(win_by_runs=0)).count()`. – Willem Van Onsem Jan 14 '19 at 11:25
I tried that before. I got the following error: `SyntaxError: positional argument follows keyword argument`. – Lax_Sam Jan 14 '19 at 11:28
2

@Laxman: sorry, the arguments indeed should be swapped, so `MyModel.objects.filter(~Q(win_by_runs=0), toss_winner=F('winner')).count()`. – Willem Van Onsem Jan 14 '19 at 11:30
Thank you! I did not think properly about the error! That solved it. – Lax_Sam Jan 14 '19 at 11:31

Django sum on query set

1 Answers1