def attach(self, id, filename, url):
        """Add an attachmemt to record from url

        :param id: ID of record
        :param filename: File name of attachment
        :param url: Public url to download file from.
        """
        Attachment = self.client.model('ir.attachment')
        return Attachment.add_attachment_from_url(
            filename, url, '%s,%s' % (self.model_name, id)
        )