How to find the difference between two columns in Django model and print result for each row in view

Question

class Daily(models.Model):
  rpt_date = models.DateField('Report Date', primary_key=True) 
  total_d_sors = models.IntegerField() 
  loaded_d_sors = models.IntegerField()
  #diff_d_count
  d_sors_missed_eod = models.CharField(max_length=300)
  total_m_sors = models.IntegerField() #monthly
  loaded_m_sors = models.IntegerField() #monthly
  m_sors_missed_eod = models.CharField(max_length=300) 

I have the above class in my models.py but when I display it through a view I need to have an additional column which will have the difference between two existing columns (total_d_sors and missed_d_sors) ie, diff_d_count=(total_d_sors - missed_d_sors)... can someone help? I'm seeing examples with cursor implementation; is there any other way?

Answer 1

Why don't you add a property on the model and calculate it on the fly as you're displaying it in your template?

class Daily(models.Model):

  @property
  def diff_d_count(self):
    return self.total_d_sors - self.missed_d_sors

Then you can access it in your template or wherever via obj.diff_d_count .

Answer 2

To find difference between 2 columns you can use,

1. annotate

2. F expression

Your query would be,

Daily.objects.annotate(diff=F('total_d_sors')-F('missed_d_sors'))

Sample working code with template,

from django.db.models import F
from django.template import Context, Template
context = Context({"daily_objects": Daily.objects.annotate(diff=F('total_d_sors')-F('missed_d_sors'))})
template = Template("{% for i in daily_objects %} {{i.id}} || {{i.diff}}. {% endfor %}")
template.render(context)