CheckedAtBooleanField

gistfile1.py

class CheckedAtBooleanField(models.DateTimeField):
    """
    A db field that acts like a checkbox in forms, but is backed by a
    DateTimeField in the database. `None` represents that the box was
    not checked, a timestamp value indicates that the box was checked
    at that time. If the form is saved again, the time is not updated.

    Specifically, the timestamp indicates when a user chose to opt in.

    When setting the attribute on the model, it's possible to use the
    values True and False. False sets the field to None. True behaves
    like checkboxes do in a form -- The field is stores the timestamp
    of the _first_ time it was True, not overriding the current value.

    There are some decisions this field doesn't make -- How should it
    behave in the admin center? Should it support filters like a bool?
    Since querying like a boolean isn't supported, use isnull instead.
    """

    def __init__(self, *args, **kwargs):
        kwargs.setdefault('null', True)
        kwargs.setdefault('blank', True)
        super(CheckedAtBooleanField, self).__init__(*args, **kwargs)

    def formfield(self, **kwargs):
        # Should this be setitem or setdefault? It depends what admin
        # should do. The admin will try to use a datetime widget here,
        # so utilizing setitem instead of setdefault we override that.
        kwargs['form_class'] = forms.BooleanField
        kwargs['widget'] = forms.BooleanField.widget
        return super(CheckedAtBooleanField, self).formfield(**kwargs)

    def save_form_data(self, instance, data):
        current_value = getattr(instance, self.attname)
        if data:
            data = current_value or timezone.now()
        else:
            data = None
        return super(CheckedAtBooleanField, self).save_form_data(instance, data)

    def contribute_to_class(self, cls, name):
        super(CheckedAtBooleanField, self).contribute_to_class(cls, name)
        setattr(cls, name, CheckedAtBooleanFieldDescriptor(self))


class CheckedAtBooleanFieldDescriptor(object):
    def __init__(self, field):
        self.field = field
        self.cache_name = self.field.get_cache_name()

    def __get__(self, instance, instance_type=None):
        if instance is None:
            return self
        else:
            return getattr(instance, self.cache_name)

    def __set__(self, instance, value):
        if value is True:
            current_value = getattr(instance, self.cache_name, None)
            value = current_value or timezone.now()
        elif value is False:
            value = None
        setattr(instance, self.cache_name, value)