helpers.py

class CreatedAtMixin(object):
    """Adds a read-only column created_at to a table

    An sqlalchemy.exc.ArgumentError will be raised it someone is trying to set
    created_at. However, the '_created' column can still be set.
    """

    _created = Column('created_at', DateTime,
                      server_default=text('NOW()'), nullable=False)

    @hybrid_property
    def created_at(self):
        """ Get the column created """
        return self._created

    @created_at.setter
    def set_created_at(self, created):
        """ Prevents the column created from being set """
        raise ArgumentError('Column created_at is read-only')