def METHOD_NAME(
    isdest, source_mapper, source_column, dest_mapper, dest_column, err
):
    if isdest:
        raise exc.UnmappedColumnError(
            "Can't execute sync rule for "
            "destination column '%s'; mapper '%s' does not map "
            "this column.  Try using an explicit `foreign_keys` "
            "collection which does not include this column (or use "
            "a viewonly=True relation)." % (dest_column, dest_mapper)
        ) from err
    else:
        raise exc.UnmappedColumnError(
            "Can't execute sync rule for "
            "source column '%s'; mapper '%s' does not map this "
            "column.  Try using an explicit `foreign_keys` "
            "collection which does not include destination column "
            "'%s' (or use a viewonly=True relation)."
            % (source_column, source_mapper, dest_column)
        ) from err