Django Money Field

Django model field for monetary amounts.

Installation

pip install django-moneyfield

Moneyfield requires:

Python ==3.3
Django ==1.5 (still working on 1.6 compatibility)
Money
Babel (if you need currency formatting)

Basic usage

from django.db import Models
from moneyfield import MoneyField

class Book(models.Model):
    name = models.CharField(blank=True, max_length=100)
    price = MoneyField(decimal_places=2, max_digits=8)

The field price will be created in the database as two columns: price_amount, and price_currency. You may use any name <fieldname>, resulting in columns <fieldname>_amount and <fieldname>_currency.

CREATE TABLE "myapp_book" (
    "id" integer NOT NULL PRIMARY KEY,
    "name" varchar(100) NOT NULL,
    "price_amount" decimal NOT NULL,
    "price_currency" varchar(3) NOT NULL
);

The attribute price is only a convenience python descriptor that accepts and returns Money objects, and will be available only when working with a model instance.

>>> book = Book.objects.get(id=1)
>>> book.price
USD 19.99
>>> book.price = Money("9.99", "USD")
>>> book.save()
>>> book.price
USD 9.99

For any operation using Managers and QuerySets, the amount and the currency must be addressed separately, using price_amount and price_currency in this case. This allows for maximum flexibility and unambiguity.

new_book = Book.objects.create(
    name="The new book",
    price_amount=Decimal("29.99"),
    price_currency="USD"
)

books_in_usd = Book.objects.filter(price_currency="USD")

cheap_books = Book.objects.filter(price_amount__lt=Decimal('2'))

cheap_books_eur = Book.objects.filter(
    price_amount__lt=Decimal('2'),
    price_currency="EUR"
)

Defaults and choices

You can provide separate defaults for the amount and the currency as Decimal and the three letter currency code string, respectively:

class Book(models.Model):
    name = models.CharField(blank=True, max_length=100)
    price = MoneyField(decimal_places=2, max_digits=8, 
                       amount_default=Decimal("0"),
                       currency_default="USD")

or a default Money value:

class Book(models.Model):
    name = models.CharField(blank=True, max_length=100)
    price = MoneyField(decimal_places=2, max_digits=8, 
                       default=Money("0", "USD"))

You can also set currency choices with currency_choices and a currency default with currency_default:

class Book(models.Model):
    CURRENCY_CHOICES = (
        ('EUR', 'EUR'),
        ('USD', 'USD')
    )
    CURRENCY_DEFAULT = 'EUR'

    name = models.CharField(blank=True, max_length=100)
    price = MoneyField(decimal_places=2, max_digits=8, 
                       currency_choices=CURRENCY_CHOICES,
                       currency_default=CURRENCY_DEFAULT)

Fixed currency

If you don't need to handle different currencies but want to benefit from using the Money class instead of just Decimals, you may want to set a fixed currency for your monetary field:

class Book(models.Model):
    name = models.CharField(blank=True, max_length=100)
    price = MoneyField(decimal_places=2, max_digits=12, currency='USD')

In this case, the attribute price will only accept and return Money objects with currency "USD". The database representation of this field will be price_amount, with no currency column. This is consistent with the multi-currency case, and allows for maximum flexibility while making schema migrations.

MoneyField options

MoneyField.max_digits

Same as DecimalField: The maximum number of digits allowed in the number. Note that this number must be greater than or equal to decimal_places.

MoneyField.decimal_places

Same as DecimalField: The number of decimal places to store with the number.

MoneyField.currency

Fixed currency for this field. This will omit the creation of a <fieldname>_currency column in the database.

MoneyField.default

Default Money value for this field (both amount and currency).

MoneyField.currency_default

Default currency value.

MoneyField.amount_default

Default amount value.

MoneyField.currency_choices

Regular Django choices iterable, e.g.:

CURRENCY_CHOICES = (
    ('EUR', 'Euros'),
    ('USD', 'US Dollars')
)

Forms

A base model form class MoneyModelForm is included to show the monetary fields as just one field in forms, instead of separate amount and currency fields.

from django.contrib import admin
from moneyfield import MoneyModelForm
from myapp.models import Book

class BookAdmin(admin.ModelAdmin):
    list_display = ['id', 'name', 'price']
    form = MoneyModelForm

admin.site.register(Book, BookAdmin)

Using MoneyModelForm is optional. You may also include it in the base classes of your custom model form class.

Using currency choices

Using fixed currency

Using free currency

Design decisions

There is already an excellent, mature, and stable package to handle money in Django: django-money.

The main difference in django-moneyfield is that the amount and currency are always created in the database as <fieldname>_amount and <fieldname>_currency, exposed in the same way in the model (alongside <fieldname>, which returns Money), and used in the same way while making queries.

This approach leads to a much simpler "model side" implementation, including efortless South compatibility. On the other hand, it makes the "modelform side" more complicated, as the user´s model field <fieldname> is not really a model Field.

For users of the package, this means making queries over separate fields <fieldname>_amount and <fieldname>_currency, which is more explicit and prevents further dependency on the package.

django-moneyfield also introduces the idea of a "fixed currency" mode, in which a currency column is not needed.

It is also designed with a Money class implementation of the same author in mind (probably compatible with other implementations, but untested).

Contributions

Contributions are welcome. You can use the regular github mechanisms.

To run the tests, sit on the package root (by setup.py) and run:

python tests/runtests.py

License

django-moneyfield is released under the MIT license, which can be found in the file LICENSE.

carlospalol / django-moneyfield