text: from django.db import models
  from django.contrib.auth import get_user_model
  
  User = get_user_model()
  
  
  class PayTxn(models.Model):
      pt_made_by = models.ForeignKey(User, related_name='transactions',
                                     on_delete=models.CASCADE)
      pt_made_on = models.DateTimeField(auto_now_add=True)
      pt_amount = models.IntegerField()
      pt_order_id = models.CharField(unique=True, max_length=100, null=True, blank=True)
      pt_checksum = models.CharField(max_length=100, null=True, blank=True)
  
      class Meta:
          db_table = u'global_paytxn'
  
      def save(self, *args, **kwargs):
          if self.pt_order_id is None and self.pt_made_on and self.id:
              self.pt_order_id = self.pt_made_on.strftime('PAY2ME%Y%m%dODR') + str(self.id)
          return super().save(*args, **kwargs)
  