this is my first question. If my question is not clear, let me know :)

So I learn Django (learning by doing) for 4 Months in my project. I have one table name material, which is the table contains material name and price. Here I will describe my table:

I want to calculate the total material price by getting the price from the table. It looks ok if I only want to get 1 price only. But, I need to get 4 values of prices from what the user wants in input. Let's say the user chooses Material 3, Material 2, Not Required and Not Required. So there is 4 material price. Then, I use a queryset like this:

x = rawmaterial.objects.filter(Q(materialName = 'Material 3') | Q(materialName = 'Material 2') | Q(materialName = 'Not Required') | Q(materialName = 'Not Required')).values_list('price',flat=True)

but the result is (900, 456, 0) not like (900, 456, 0, 0). I have been trying with SQL query using OR, is there any possibility to get 4 values? Thank you :)

CodePudding user response：

You can't query like that. Filter will filter out the values, not make them 0. Instead, you can use Conditional Expression. In your case, you can consider Case:

from django.db.models import Case, Value, When, F

rawmaterial.objects.annotate(
     required_prices=Case(
         When(materialName__in =['Material 3','Material 2', 'Not Required'], then=F('price')),
         default=Value(0),
     )
).values_list('required_prices', flat=True)

FYI, please follow the pep-8 style guide for naming class name (Pascal Case) and field/function names (snake case).