Find first record subject to restrictions in +kwargs+, raising
        RecordNotFound if no such record exists.

def find_by(self, **kwargs):
        """
        Find first record subject to restrictions in +kwargs+, raising
        RecordNotFound if no such record exists.
        """
        result = self.where(**kwargs).first()
        if result:
            return result
        else:
            raise RecordNotFound(kwargs)