Django custom field validator vs. clean

Question

I would like to create TodayOrLaterDateField() which would subclass DateField() field as I am using this condition in many places. The purpose of this field would be avoiding putting dates from the past.

What is the most straightway way of doing this? I am confused with validator vs. clean method. I've tried with clean() but when comparing value to datetime.date.today() I am getting "compare unicode object to date" error.

I'm using Django 1.3

Answer 1

Validators only validate, they don't return the improved format; Clean methods both validate and return a (sometimes amended) value.

I think the way to go here is to just use a DateField with a validator as a inherited class of DateField with a default_validators set.

import datetime
from django.core import exceptions
from django.db import models
from django.utils.translation import ugettext_lazy as _

def validate_date_today_or_later(value):
    'Place this in validators.py and import it to keep your model a bit cleaner'
    if value < datetime.date.today():
        raise exceptions.ValidationError(_('Date must be today or later'))

class TodayOrLaterDateField(models.DateField):
    default_validators = [validate_date_today_or_later,]

edit: You can apply the same validator to your form fields as well if you just want it there and not in your whole app.

Answer 2

You can extend models.DateField and override to_python method. Didn't tested on Django 1.3 but should work.

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

class TodayOrLaterDateField(models.DateField):
    def to_python(self, value):
        value = super(TodayOrLaterDateField, self).to_python(value)
        if value < datetime.date.today():
            raise exceptions.ValidationError(u'Date must be today or later')
        return value