django-pursed

A simple wallet django app.

Creating a New Wallet

A wallet is owned by a user. Should you be using a custom user model, the wallet should still work properly as it the wallet points to settings.AUTH_USER_MODEL.

from wallet.models import Wallet

# wallets are owned by users.
wallet = user.wallet_set.create()

Despositing a balance to a wallet

from django.db import transaction

with transaction.atomic():
    # We need to lock the wallet first so that we're sure
    # that nobody modifies the wallet at the same time 
    # we're modifying it.
    wallet = Wallet.select_for_update().get(pk=wallet.id)
    wallet.deposit(100)  # amount

Withdrawing a balance from a wallet

from django.db import transaction

with transaction.atomic():
    # We need to lock the wallet first so that we're sure
    # that nobody modifies the wallet at the same time 
    # we're modifying it.
    wallet = Wallet.select_for_update().get(pk=wallet.id)
    wallet.withdraw(100)  # amount

Withdrawing with an insufficient balance

When a user tries to withdraw from a wallet with an amount greater than its balance, the transaction raises a wallet.errors.InsufficientBalance error.

# wallet.current_balance  # 50

# This raises an wallet.errors.InsufficentBalance.
wallet.withdraw(100)

This error inherits from django.db.IntegrityError so that when it is raised, the whole transaction is automatically rolled-back.

Transferring between wallets.

One can transfer a values between wallets. It uses withdraw and deposit internally. Should the sending wallet have an insufficient balance, wallet.errors.InsufficientBalance is raised.

with transaction.atomic():
    wallet = Wallet.select_for_update().get(pk=wallet_id)
    transfer_to_wallet = Wallet.select_for_update().get(pk=transfer_to_wallet_id)
    wallet.transfer(transfer_to_wallet, 100)

CURRENCY_STORE_FIELD

The CURRENCY_STORE_FIELD is a django field class that contains how the fields should be stored. By default, it uses django.models.BigIntegerField. It was chosen that way for simplicity - just make cents into your smallest unit (0.01 -> 1, 1.00 -> 100).

You can change this to decimal by adding this to your settings.py:

# settings.py
CURRENCY_STORE_FIELD = models.DecimalField(max_digits=10, decimal_places=2)

You need to run ./manage.py makemigrations after that.