CODEWITHSUNDEEP
djangodjango-modelsdjango-views
Jakub
Jakub

Reputation: 303

Django - filtering on added property to model

I would like to add some property to my model, which stores quantities of some parts, and then filter and order by this property :

models.py

class MAG_warehouse(models.Model):
   id_part=models.OneToOneField(MAG_magazyn)
   qty_min=models.IntegerField()
   qty=models.IntegerField()

views.py

def view(requst):
   alert_qty=1.5 #relative quantity, when part should be bought
   parts=MAG_warehouse.objects.all()
   for item in parts:
      item.rel_qty=float(item.qty)/item.qty_min
      if item.rel_qty <=alert_qty:
          item.color="red" #for css styling
          item.alertflag=1
      else:
          item.alertflag=0
   #What i would
   #like to have:
   sorted_parts=parts.filter(alertflag__exact=1).order_by('rel_qty')

but unfortunately I have attribute error. Without filtering/ordering I can see item.rel_qty and item.color in template.

How can I filter and order my objects by added attribute?

Upvotes: 1

Views: 98

Answers (3)

allo
allo

Reputation: 4236

You can try to use .values() (actually fetch the values from db) and amend the resulting list with the additional properties.

Upvotes: 0

iamroot
iamroot

Reputation: 71

As you told you are getting Attribute error bcoz of filter and order_by, but i think your code is right below is the example. i'm sure the attribute error object is not in your property/ or not in your object instance.i got right output. if you provide the snap of you error, will help in finding your solution.

>>> from .models import Model
>>> instances = Model.objects.all()
>>> sorted_instance = instances.filter(column1__exact=45).order_by('column2')
>>> sorted_d
[<Model: Not Finalized>, <Model: Finalized>, <Model: Orderised>, <Model: unordered>]
>>>

Upvotes: 0

Ben Hare
Ben Hare

Reputation: 4415

Django's .filter and .order_by are database operations, since you're adding color/rel_qty/alertflag to the objects but they aren't present on the database you can't use them. You'll have to use Python, something like 

sorted_parts = sorted([part for part in parts if part.alertflag == 1], key=lambda part: part.relqty)

Although you could write that a couple other ways to be sure.

Upvotes: 1

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