def get_col(self, alias, output_field=None):
        """Get the decryption for col."""
        if output_field is None:
            output_field = self
        if alias != self.model._meta.db_table or output_field != self:
            return DecryptedCol(
                alias,
                self,
                output_field
            )
        else:
            return self.cached_col
Get the decryption for col.