I am reading the Hibernate-In-Action book. In chapter 3, it has a bi-directional many-to-one relationship. Bid and Item.



My question is if I want query an Item by ID and Bid.amount = 10.0, what is the most efficient to do it?

One thing I think of is this:


Is there a better way to do it? I think doing this will require loading all bids of that item to the memory from database. I am trying to come up a better way.

Thank you.

You have:
Item item = itemDAO.getItemByID(itemId);

then, one query could be:

Query q = sess.createQuery("from Bid b where b.amount =10 and b.oneItem = :myitem");
q.setEntity("myitem",item);
List ListBids = q.list();

then you can iterate the list.

For example, if in your Bid.hbm.xml mapping file, you have
<many-to-one
name="oneItem"
class="encuestas.Item"
> .....
you must put the same name of the class in the name of propiety of the query for quering a entity (b.oneItem)

This help you???

Sorry, in
<many-to-one
name="oneItem"
class="your_package.Item"
> .....

your_package is just that, el name of your package, where Item is.

Thanks. But which query is faster:
Is this faster than your suggestion:


your original:



or they don't make any difference?

The when I see the native mysql that query you generated. It has more conditions in the query (every property of item has a condition). I wonder if that results in a slower query.

Thank you.

If my solution generate more conditions, maybe it's more direct to acces database, Your

Query q = sess.createQuery("from Bid b where b.amount =10 and b.oneItem.id = :myitemid");
q.setLong("myitemid",item.getId().longValue());
List ListBids = q.list();

retrieve id again, in item.getId.longValue(), I think, is redundant, but I just think its better of your

Item item = itemDAO.getItemByID(itemId);
// loop thru in java code to find the amout = 10.0
Set itemBids = item.getBids();
for (Iterator iter = itemBids.iterator(); iter.hasNext();) {
(Bid) element = (Bid) iter.next();
if (element.amount == 10.0) {
// found ....
....
}

}

Maybe we need calculate what order have all