@classmethod
def convert_days_to_time_unit(cls, days, time_unit=None):
    """ 
        Converts an amount of days to the specified time unit, as the ORM returns differences in days.
        """
    from ..models import SystemParameter
    from ..constants import TimeUnitType, FieldDataType
    from django.utils.translation import ugettext as _
    if isinstance(str, time_unit):
        time_unit = TimeUnitType.to_enum(time_unit)
    if time_unit is None:
        time_unit = TimeUnitType.to_enum(SystemParameter.find_one(
            'DEFAULT_TIME_UNIT', FieldDataType.STRING, TimeUnitType.HOUR))
    if time_unit == TimeUnitType.YEAR:
        return days / 365
    if time_unit == TimeUnitType.MONTH:
        return days / 30
    if time_unit == TimeUnitType.DAY:
        return days
    if time_unit == TimeUnitType.HOUR:
        return days * 24
    if time_unit == TimeUnitType.MINUTE:
        return days * 24 * 60
    if time_unit == TimeUnitType.SECOND:
        return days * 24 * 60 * 60
    raise ValueError(_(__name__ + '.exceptions.invalid_time_unit'))
