Confused about distinct/aggregate queries with (N)Hibernate

I'm not sure how to approach queries that don't map 1:1 to my persistent entities - in other words, distinct and aggregate queries. For开发者_JAVA百科 example, I need to retrieve a distinct list of property values for populating a drop-down list.

Should I write a class and a mapping for the "entities" that are returned by this query? Or should I just use the native DB provider and work with native data sets instead?

If I understand correctly, your problem can be solved by scalar queries in HQL. For example:

Query q = session.createQuery("select i.id, i.description, i.initialPrice" +
    "from Item i where i.endDate > current_date()");

Iterator results = q.list().iterator();
while ( results.hasNext() ) {
  Object[] result = (Object[]) results.next();
  Long id = (Long) result[0];
  String description = (String) result[1];
  BigDecimal price = (BigDecimal) result[1];
}

You can also use distinct in such queries.

Here is another example.

Of course the same can also be done using native SQL from within Hibernate.

If the aggregate query is really complex, create a view from the aggregate query and a read-only mapping to the view.