How to update a FloatField: Django - django

Question

I'm trying to update field in my models with the newly calculated value from my view and when I try to update my field using total.objects.update(total=total) this is what i get 'decimal.Decimal' object has no attribute 'objects'.
I also have some other questions, I'm currently calculating the total field from initial values inputted when the item is created, using the save() method. is this a good idea ? or is there a better way of doing this? the reason I'm currently doing this is because i display the a list of items with their initial values.
Over all I'm trying to make a tools inventory system. I also have some other concerns.
How can I use this view on multiple items types? the model items is an abstract model that contains all common fields,and every tool type inherits this model and will be using the same operations, calculate the new cantidad_existente and update the total fields. Is there a better way?
my views.py
def calcular_nueva_cantidad(ce, up):
total = ce + up
return total
class updateForm(forms.Form):
update = forms.IntegerField()
def actualizar_cantidad(request, pk):
# trae de la base de datos el valor de la cantidad existente
cantidad_existente = Cortadores.objects.filter(pk=pk).values('cantidad_existente')
c = cantidad_existente.values_list('cantidad_existente', flat=True)
ce= c[0]
# trae de la base de datos el valor de precio_unitario
precio_unitario = Cortadores.objects.filter(pk=pk).values('precio_unitario')
p = precio_unitario.values_list('precio_unitario', flat=True)
pu =p[0]
# trae de la base de datos el valor de la total
total = Cortadores.objects.filter(pk=pk).values('total')
print(F'el precio unitario es {total} ----------------------------------------------------')
if request.method =='POST':
form = updateForm(request.POST)
if form.is_valid():
up = form.cleaned_data['update']
nce = calcular_nueva_cantidad(up, ce)
total = nce * pu
print(F' el nuevo total es {total} -----------------------')
# nce.save()
cantidad_existente.update(cantidad_existente=nce)
total.objects.update(total=total)
return render(request, 'inventario/cortadores.html', {'nce':nce})
else:
# Redirect to fail page after POST
return HttpResponse('')
else:
form = updateForm()
return render(request, 'inventario/update-cortador.html', {'form':form, 'cantidad_existente':cantidad_existente })
my models.py
class Item(models.Model):
description = models.CharField(max_length=30,)
numero_parte = models.CharField(max_length=30)
proveedor = models.ForeignKey(Proveedor, on_delete=models.CASCADE)
cantidad_existente = models.PositiveIntegerField()
update = models.PositiveIntegerField(blank=True, default=0)
cantidad_minima = models.PositiveIntegerField()
precio_unitario = models.DecimalField(max_digits=5, decimal_places=2)
total = models.FloatField(blank=True)
asignado_a = models.ForeignKey(Empleados, on_delete=models.CASCADE, blank=True, null=True)
anaquel = models.CharField(max_length=2, choices=ANAQUEL, blank=True, null=True)
posicion_en_x = models.CharField(max_length=2, blank=True, null=True)
posicion_en_y = models.CharField(max_length=2, blank=True, null=True)
activo = models.BooleanField()
class Meta:
abstract = True
def save(self,*args,**kwargs):
self.total = self.cantidad_existente * self.precio_unitario
super().save(*args,**kwargs)
class Cortadores(Item):
tipo = models.ForeignKey(Tipos_Cortadores,on_delete=models.CASCADE)
material = models.ForeignKey(Materiales, on_delete=models.CASCADE)
filos = models.CharField(max_length=5, choices=GABILANES)
diametro = models.ForeignKey(Diametros, on_delete=models.CASCADE)
longitud = models.ForeignKey(Longitud, on_delete=models.CASCADE)
desbaste = models.CharField(max_length=1, choices=DESBASTE)
class Meta:
verbose_name_plural = "Cortadores"
def get_absolute_url(self):
return reverse('inventario:cortadores-list', kwargs={'id': self.id})
def __str__(self):
return '%s %s %s %s %s %s' % ( str(self.tipo), str(self.material), str(self.filos), str(self.diametro),
self.longitud, self.desbaste
)

Answer 1

The error is that you have two variables called total. Just rename one of them.
total = Cortadores.objects.filter(pk=pk).values('total')
...
new_value = nce * pu
total.objects.update(total=new_value)

Answer 2

There is a error, you changing you queryset to flaot value, and then trying to use queryset functions on it, so you should use other variable in total and not your own queryset
total = Cortadores.objects.filter(pk=pk).values('total')
total = nce * pu // This line replace your queryset to float
total.objects.update(total=total)
You should use something like that
qs_total = Cortadores.objects.filter(pk=pk).values('total')
total = calcular_nuevo_total(nce, pu)
for value in qs_total:
value.total=total
value.save()
To use it as generic like you want use pass the class reference as parameter and use it to call your query set
def something(__class__):
class.objects.all()
EDIT: Making a generic method to use with any class
from .models import Cortadores, OtherModelExample
def generic_update_noreturn(__class__, pk, total)
qs= __class__.objects.filter(pk=pk).values('total')
for value in qs:
value.total=total
value.save()
return qs
def generic_update_noreturn(__class__, pk, total)
__class__.objects.filter(pk=pk).values('total')update(total=total)
def actualizar_cantidad(request, pk):
...
total = calcular_nuevo_total(nce, pu)
updated_cortadores=generic_update(Cortadores, pk, total)
updated_otherexample=generic_update(OtherModelExample, total, pu)
generic_update_noreturn(Cortadores, pk, total)