Question

I have an existing PostgreSQL database that I’m using for a new Django site. When I run:

python manage.py inspectdb

I get several fields which have the PostgreSQL type of “money” that do not convert correctly. To Django’s credit, they at least tell you that they are guessing. 🙂

In the PostgreSQL documentation, they provide the following information for the money type:

Name: money
Storage Size: 8 bytes   
Description: currency amount    
Range: -92233720368547758.08 to +92233720368547758.07

It seems like to me that this should be a DecimalField in Django.

How have other people handled this? And if you have run into this problem before, did you discover any “gotchas”? Anything that I should be aware of, etc?

Version info:

PostgreSQL 9.1 with Python 2.6.5 and Django 1.3.1

Answer 1

Here is what I did for this problem. I defined a custom field subclassed from CharField and then added a custom validator. Note: I ran into problems with the DecimalField validating correctly in the admin module (I guess you could call this one of the “gotchas” I was asking about!). I have created unit tests for the code and test via the admin pages, and it seems to work fine.

from django.db import models
from django.core import exceptions
import re


MONEY_REGEX_PATTERN = re.compile('^\$?-?0*(?:\d+(?!,)(?:\.\d{1,2})?|(?:\d{1,3}(?:,\d{3})*(?:\.\d{1,2})?))$')

def MoneyValidator(value):
    """Will validate a string value against a money regular expression"""
    if not MONEY_REGEX_PATTERN.match(value):
        raise exceptions.ValidationError('{v} is not a valid dollar amount'.format(v=value))


class MyMoneyField(models.CharField):

    """Custom field for handling values from PostgreSQL's money data type"""

    def __init__(self, *args, **kwargs):
        kwargs['validators'] = [MoneyValidator]
        kwargs['max_length'] = 20
        super(MyMoneyField, self).__init__(*args, **kwargs)