Styjun

I'm trying to sort a queryset of dictionaries to which I added some calculated values.

The process:

class Inventario(models.Model):
 codigo_kinemed = models.CharField(max_length=100)
 existencias = models.IntegerField(help_text="Existencias ", blank=True, null=True)
 valor_coste = models.IntegerField(help_text="Existencias ", blank=True, null=True)
 valor_venta = models.IntegerField(help_text="Existencias ", blank=True, null=True)
 fecha = models.DateField(help_text="Fecha de toma de datos", blank=True, null=True)

 def __str__(self):
 return str(self.codigo_kinemed)

I get a queryset from that.

inventario_diferencia = Inventario.objects.filter(fecha=ultima_fecha_cargada.fecha).values()

That returns a queryset of dictionaries. Then I iterate over that queryset and calculate some new fields.

for este in inventario_diferencia:
 este['stock_valor_venta'] = este['existencias'] * este['valor_venta']

I can print that calculated field with no problem in the template.

 inventario_diferencia.stock_valor_venta 

Ordering

I want to sort that queryset by the new stock_valor_ventavalue I added.

When I try the usual queryset

inventario_diferencia.order_by('stock_valor_venta')

I get:

Cannot resolve keyword 'diferencia_mes' into field. Choices are: codigo_kinemed, existencias, fecha, id, valor_coste, valor_venta

Those are the model´s original values, so no option to order by the new value. When I try to sort it like a dictionary

inventario_diferencia = sorted(inventario_diferencia, key=lambda t: t.diferencia_mes)

I get

'dict' object has no attribute 'diferencia_mes'

Documentation

In the Django doc https://docs.djangoproject.com/en/2.1/ref/models/querysets/#values states the following:

values(*fields, **expressions) Returns a QuerySet that returns dictionaries, rather than model instances, when used as an iterable.

Is my problem related to the "when used as an iterable" part of the statement? How can I sort that kind of querysets by added values?

Thanks in advance!

You should look into using annotate. You could create the a field that is equal to the product of your two fields then order by that in SQL.

from django.db.models import F
inventario_diferencia = Inventario.objects.filter(
 fecha=ultima_fecha_cargada.fecha
).annotate(
 stock_valor_venta=F('existencias') * F('valor_venta')
).order_by('-stock_valor_venta')

print(inventorio_deiferencia.first().stock_valor_venta)