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Hibernate version: NHibernate 1.0.2

I've got some strange behavior with an HQL statement and I'm not sure whether or not it's by design - hopefully someone can clarify for me.

I have a domain model where there are Parent objects and Child objects where the Parent object has a collection of children - Parent.Children.

Assuming there are 2 Parents in the DB and Parent #1 has 1 child and Parent #2 has 2 Children I would expect the following HQL query to return two Parent obects with the Children property collections populated.




This assumption is based on the following from the documentation:



What I'm getting, however, is 3 Parent objects: 1x Parent #1 and 2x Parent #2.

Have I misunderstood the documentation? Or is something else not right here?

Symon.[/quote]

I'm afraid this is by design. In the past, I also ran into this issue and it appeared to be by design. Still don't know the exact reason for it though.

I worked around this issue by creating a small utility class that filters the duplicates.

Seems strange that it's by design when the docs seem to be contradictory. I'll have to look into why.

Thanks for the suggestion on the filtering though.

Cheers,

Symon.

OK, after reading the FAQ and doing a little digging on the forums I'm still pretty much in the dark over why there's a discrepancy between what the docs say and the actual result.

The Hibernate FAQ entry entitled "Hibernate does not return distinct results for a query with outer join fetching enabled for a collection (even if I use the distinct keyword)" says:



But *why*? This means that I need to know whether the query is going to perform an outer join fetch to know whether or not I need to distinctify the results. Otherwise, I might remove duplicate instances that are supposed to be in a result set, right?

I've been putting together a web service API to allow users to execute arbitrary HQL queries against my domain model. To do this I've generated proxy classes with an IsLazy property and am making all lazy objects and collections in the query result set return an unpopulated proxy marked lazy. It was my intention to allow the user to populate a selected collection property of each returned object by using the "join fetch" HQL construct, but then it skews the result set.

I suppose I could try parsing the HQL statement for "join fetch" to determine whether or not I need to distinctify the results, but this just seems like a bit of a kludge.

Why was the choice was made to make the result set match the size of the underlying DB result set? This should probably be in the docs since it directly contradicts what's currently written there.

Cheers,

Symon.

Martijn_b: Do you really need your own utility class? I had one too, but I could use: .SetResultTransformer(CriteriaUtil.DistinctRootEntity);
on my queries to let nh do it.

Maybe on straight hql you can't?

Is this when using the Criteria API? I only ran into this with straight hql (via IQuery). Looks like a good solution though. Maybe something like this also exists in the IQuery interface and I just overlooked it.

yes, this is using the criteria api

ICriteria c = s.CreateCriteria(typeof(Functie))
.SetFetchMode("RolIDs", FetchMode.Join)
.AddOrder(new NHibernate.Expression.Order("Naam", true))
.SetResultTransformer(CriteriaUtil.DistinctRootEntity);

LijstEntiteiten<Functie> functies = new LijstEntiteiten<Functie>(c.List());

I'd be interested in an iQuery method for it as well. ;-)