Eager loading a tree in NHibernate

Question

I have a problem trying to load a tree, this is my case, I have an entity associated with itself (Hierarchic) with n levels; the question is, Can I load eagerly the entire tree using ICriteria or HQL?

Thanks in advance for any help. Ariel

Answer 1

Yes... just set correct fetchmode.

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i'll include example in a minute.

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Example taken from here =>

IList cats = sess.CreateCriteria(typeof(Cat))
    .Add( Expression.Like("Name", "Fritz%") )
    .SetFetchMode("Mate", FetchMode.Eager)
    .SetFetchMode("Kittens", FetchMode.Eager)
    .List();

You can specify to eager load child of child too =>

.SetFetchMode("Kittens.BornOn", FetchMode.Eager)

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In case you are using Linq to NHibernate, use Expand method =>

var feedItemQuery = from ad in session.Linq<FeedItem>().Expand("Ads")
                           where ad.Id == Id
                           select ad;

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And i would recommend to use helper method that creates string from passed in lambda expression.

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Quite likely that it's possible to tell Criteria to load whole tree. But i'm not aware about that and i prefer specifying what exactly i need (seems dangerous to load everything).

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Does this helps?

Answer 2

This article contains a solution for fetching the entire tree using NHibernate. See the sub-heading "Eager load ancestors and descendants". The author uses a hierarchical query in SQL Server 2005.