django queryset aggregate multiple operations fields

Question

model.py

class Fatture(models.Model):
    numero = models.CharField(max_length=30, null=True, blank=True)
    data =  models.DateField()
    iva  =  models.PositiveIntegerField()
    commissione =  models.DecimalField(max_digits=6, decimal_places=2, null=True, blank=True)

class Ddts(models.Model):
    fattura = models.ForeignKey('Fatture') 

class DdtsArticoli(models.Model): 
    ddt = models.ForeignKey('Ddts')
    articolo = models.ForeignKey('Articoli')
    quantita = models.DecimalField(max_digits=6, decimal_places=2)
    prezzo =  models.DecimalField(max_digits=6, decimal_places=2, null=True, blank=True)
    colli  =  models.PositiveIntegerField()

I have to make a query that calculate this total:

aggregate table DdtsArticoli SUM(quantita * prezzo)
aggregate table DdtsArticoli ((quantita * prezzo) / (1 + (iva of table Fatture)/100 ))
resut of 1) - result of 2)

What do you group by? Or you want the total sum of the whole table? — Ilian Iliev
– Ilian Iliev, Commented Apr 29, 2015 at 17:57

Klaus D. · Accepted Answer · 2015-04-30 05:55:18Z

1

See the Django docs on aggregation for detail but 1. should be something like:

from django.db.models import Sum

DdtsArticoli.objects.all().aggregate(
    your_key=Sum(F('quantita') * F('prezzo'), output_field=FloatField()))

Number 2. is no aggragation, you can simply calculate it:

(obj.quantita * obj.prezzo) / (1 + (obj.ddt.fattura.iva/100.0))

Where obj is your object aka. your database row.

Number 3. should be trivial then.

answered Apr 30, 2015 at 5:55

Klaus D.

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