Django : Updating model by overriding save method

Question

This is my first model

from django.db import models
from django.contrib.auth.models import User

CHOICES = (('Earned Leave','Earned Leave'),('Casual Leave','Casual Leave'),('Sick Leave','Sick Leave'),('Paid Leave','Paid Leave'))
STATUS_CHOICES = (('0', 'Rejected'),('1', 'Accepted'),)


class Leave(models.Model):

    employee_ID = models.CharField(max_length = 20)
    name = models.CharField(max_length = 50)
    user = models.ForeignKey(User, on_delete = models.CASCADE, null =True)
    type_of_leave = models.CharField(max_length = 15, choices = CHOICES)
    from_date = models.DateField()
    to_date = models.DateField()
    status = models.CharField(max_length = 15, choices = STATUS_CHOICES)

    @property
    def date_diff(self):
        return (self.to_date - self.from_date).days

This is my second model

class History(models.Model):

    first_name = models.CharField(max_length = 50)
    last_name = models.CharField(max_length = 50)
    employee_ID = models.CharField(max_length = 20)
    earned_leave = models.IntegerField()
    casual_leave = models.IntegerField()
    sick_leave = models.IntegerField()
    paid_leave =models.IntegerField()

Here upon saving the first model Leave , I have written to override save method like,

def save(self, *args, **kwargs):
        super(Leave, self).save()
        if  self.employee_ID == History.employee_ID:
            if self.status == '1':
                if self.type_of_leave == 'Earned Leave':

                    history = History.objects.update(
                earned_leave = self.date_diff,  
                )

But upon saving the first model, all the entries in the History model are getting updated. Where in the history table every user have a separate entry with user's details( first_name, last_name, employee_ID ) and default values as 10 for the rest. Upon saving the Leave model only the entry that is associated with the employee_ID of Leave model should be updated in the History model. For that purpose i have given as if self.employee_ID == History.employee_ID: but it isn't working.

I've even tried as -

def save(self, *args, **kwargs):
            super(Leave, self).save()
            if  self.employee_ID == History.employee_ID:
                if self.status == '1':
                    if self.type_of_leave == 'Earned Leave':

                        history = History.objects.update(
                    earned_leave = History.earned_leave - self.date_diff,  
                    )

But this is not working, nothing gets updated and get'a an error unsupported operand types

So, the base of the project is employee-leave-management. As the user applies for the leave and is accepted the number of days left should get updated in History table or model.

If there's any alternate method, share.

Answer 1

History.objects.update(...) does in fact update all the History objects. You should specify which ones you want to update in your query:

from django.db.models import F

def save(self, *args, **kwargs):
    super(Leave, self).save()
    if self.status == '1':
        if self.type_of_leave == 'Earned Leave':
            history = History.objects.filter(employee_id=self.employee_id).update(
                earned_leave = F('earned_leave') - self.date_diff,  
            )

The F() expression here refers to the value of the column and will be computed by the database rather than in Python.