SUM columns in Django

Question

I have a simple model that collects data (specifically integers) to display an election results in a table. I have 2 regions (more of course but let's say two for now) where data will be coming from. I want to display each regions and the total for each region and then display the SUM at the bottom of the table

My base model is as follows;

class Results(models.Model)
    region_number = models.Foreignkey(Regions)
    region_name = models.Charfield()
    polling_station = models.Charfield()
    party1 = models.IntegerField()
    party2 = models.IntegerField()
    party3 = models.IntegerField()

Then I have two class inheritance

class GeneralElections(Results)
    pass

class RegionalElections(Results)
    pass

And I want the printed output in my template to look something like this

---------------------------------
regions   party1   party2  party3
---------------------------------
1         20       40      60
2         20       80      100
---------------------------------
Total     80       120     160    <------- More Importantly This!
---------------------------------

Additionally I want to be able to have summary page that shows

   General Elections
-----------------------
party1   party2  party3
-----------------------
80       120     160


   Regional Elections
-----------------------
party1   party2  party3
-----------------------
50       85      210

Up to this point I have been able to accomplish everything, except being able to print the SUM of each column at the bottom of the table

Everywhere I've looked it said to use django aggregation. However the instructions are a bit vague. Maybe because I am a beginner. I am confused where to put the respective codes for example.

from django.db.import SUM

1. Where does this import go? In models.py? or views.py?

total = Tally.objects.aggregate(Sum("field_name"))

2. Where do I put this function?

3. Which field_name do I use? The are multiple field names I want SUM for. One for each party

I apologize if this has been answered before but I am strapped for time and I couldn't find any detailed information regarding this.

I greatly appreciate if someone can point me in the right direction and save me a lot of time as I need to get this app online in a matter of hours.

Thank you in advance!

Answer 1

For sum per fields you can use something like:

from django.db.models import Sum

agrregated_results = Results.objects.filter(# if you have any).agrregate(Sum('party1'), Sum('party2'), Sum('party3'))
party1_sum = agrregated_results['party1__sum'] or 0
... # same for other fields

and for regions summary page:

region_summary = Results.objects.values('region_number').annotate(party1_sum=Sum('party1'), party2_sum=Sum('party2'), party3_sum=Sum('party3')).order_by()

, where .values(...).annotate(...).order_by() is translated into:

SELECT fields_in_values_plus_annotation FROM table_name GROUP BY fields_in_values ORDER BY NULL;