Hi

I am a NHibernate / Castle ActiveRecord user and ran into the following problem.

I have a root entity A which has a bag of Bees and Cees.

When eager fetching both the collections:

DetachedCriteria query = DetachedCriteria.For<A>(alias ?? "a");

query.SetFetchMode("Bees", FetchMode.Join);
query.SetFetchMode("Cees", FetchMode.Join);

the collection items are duplicated.

Say A has 2 bees and 3 cees, with eager fetch a.Bees & a.Cees both have a count of 6.

Believe this is due to the left joins that hibernate generates.

Setting the SetResultTransform(Transformers.DistinctRootEntity) makes no difference.

QUESTIONS:

1. Is there any other transformer which would eliminate the duplicates in the child collections?

2. Is using a set instead of a bag the preferred way to eliminate duplicates (if so can I map an ICollection<T> to a set)

Also are there any performance implications for using a set as opposed to a bag.

3. Also is there any good info on why hibernate does not try to eliminate duplicates by default?

Thanks

Ajai

I am not aware of other duplicate-eliminating transforms.

DistinctRootEntity will eliminate duplicates in the first table of a two-way join, but does not scale to n-way joins.

Rather than expecting NHib to puzzle through the cartesian product of an n-way join, simplify your code to return just two tables at a time.

First get A-Bees, then A-Cees, or let one of the collections be lazy-fetched.

I can do that, but the same problem exists if say:

A has list of Bees (FetchMode.Join)
B has list of Cees (FetchMode.Join)

As a dev, not knowing anything better, I might specify there eager fetches as part of mapping file itself.

Which brings me back to my original question:

Is using a set as opposed to a bag the preferred method for domain mapping?

If so does NHibernate support mapping a ICollection<T> to Isei set?