title: How to decrease the days remaining when the days are passed
body: <p>Thank you in advance,
  I am new to Django rest
  I am creating a JobsPortal website with Django rest but the problem is when the days pass the days remaining is still the same. How to decrease the days remaining when the days are passed. And also how to delete the data automatically after the before date is passed.</p>
  <p>My model</p>
  <pre><code>class Jobs(models.Model):
      post_date=models.DateField( default=_datetime.date.today, blank=False,editable=False)
      before_date=models.DateField(blank=False,)
      days_left=models.IntegerField(null=True, blank=True)
      
       def save(self,*args, **kwargs):
          self.days_left=((self.before_date - self.post_date).days)
          if self.days_left&gt;=0:
            super(Jobs, self).save(*args, **kwargs)
          else:
              return  False
  </code></pre>