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✅
I think you can use django post_save
see this https://docs.djangoproject.com/en/1.9/ref/signals/#post-save
Update your models.py with the below codes
def update_money(sender, instance, created, **kwargs):
if created:
gate = Gateway.objects.get(id = instance.gate_id )
gate.money = gate.money + transaction.amount
gate.save()
signals.post_save.connect(update_money, sender=Transactions)
Source:stackexchange.com