Sum numbers and group them by the given month, is there a 'best practice'?

September 4, 2022

I don’t know what I messed up.

I tried so many methods and solutions and so far this works the best, but the ordering is messy.
I want to sum the expenses grouped by the month extracted from the datefield it was given.

So far I made this:

def index(req):
    qs = Expense.objects.filter(pom='OUT').annotate(month=TruncMonth('when')).values('month').annotate(total_amount=Sum('amount')) # pom='OUT' -- expense (there are expenses and incomes)
    return render(req, 'index.html', {'data': qs})

which works perfectly, returns them as "sept. 15.000, aug. 10.000" which is nice! But the last/latest month is always at the bottom so I wanted to give it an order_by, which returns each unique object in the model (so if sept. 15.000 came up as sept.15 10.000 and sept.22 5.000, when they’re not summed up but returned/shown separately).

What did I mess up?

EQ:
The mentioned query (without order_by) returns a queryset as of
<QuerySet [{'month': datetime.date(2022, 8, 1), 'total_amount': 15000.0}, {'month': datetime.date(2022, 9, 1), 'total_amount': 16000.0}]> by default making it look they all have been recorded at the start of the given month.

Drop a reply for further information if I forgot to include something/explained something poorly!

>Solution :

Try this:

Expense.objects.filter(pom='OUT')\
    .values('when__year', 'when__month')\
    .annotate(total_amount=Sum('amount'))\
    .order_by('-when__year','-when__month')

I included the year, otherwise it will add total_amount of next years months to this years months. Remove the - if you need an ascending order.

This will yield a result like:

<QuerySet [
    {'when__year': 2022, 'when__month':9, 'total_amount': 15000.0}, 
    {'when__year': 2022, 'when__month':8, 'total_amount': 16000.0}
]>

Edit:

Expense.objects.filter(pom='OUT')\
    .annotate(
        total_amount=Sum('amount'),
        year=models.F('when__year'),
        month=models.F('when__month')
    ).order_by('-year','-month')