@Override
@SuppressWarnings("unchecked") // workaround to
// keep accessors fully typed without additional
// generic arguments to iterator itself
public Future<?> apply(SqlParameterSource params) {
DataSourceAccessor ungeneric = sources;
NamedParameterJdbcOperations npjo = ungeneric.get(params);
Worker worker = new Worker(npjo, params);
return executor.submit(worker);
}