The other problem is fetching multiple collections in the same graph.

That's a problem if done through JOIN, of course because it can lead to Cartesian Product issues. Even if we add support for FetchType.SELECT and you have N records selected by the first query, you will get a N+1 query issue.

When it comes to fetching data, it's ultimately the data access layer method to figure out he most efficient way of doing it. It's unlikely that any annotation set at mapping time will be suitable for all scenarios.