Source code for accounts.signals

from django.db.models import F
from django.db.models.signals import pre_delete, pre_save, post_save
from django.dispatch.dispatcher import receiver

from entries.models import Transaction

from .models import Account


@receiver(pre_save, sender=Transaction)
def transaction_presave(sender, instance, **kwargs):
    """Refund Account balances if updating a Transaction."""
    if instance.id:
        old_instance = Transaction.objects.get(id=instance.id)
        Account.objects.filter(id=old_instance.account.id).update(
            balance=F('balance') - old_instance.balance_delta)


@receiver(post_save, sender=Transaction)
def transaction_postsave(sender, instance, **kwargs):
    """Change Account Balance on Save."""
    Account.objects.filter(id=instance.account.id).update(
        balance=F('balance') + instance.balance_delta)


@receiver(pre_delete, sender=Transaction)
def transaction_delete(sender, instance, **kwargs):
    """Refund Transaction before deleting from database."""
    Account.objects.filter(id=instance.account.id).update(
        balance=F('balance') - instance.balance_delta)