NHibernate Linq and DistinctRootEntity

Question

When I execute the following query, I get an exception telling me that 'feedItemQuery' contains multiple items (so SingleOrDefault doesn't work). This is expected behaviour when using the Criteria api WITHOUT the DistinctRootEntity transformer, but when using linq, I expect to get a single root entity (FeedItem, with the property Ads (of ICollection) containing all Ads).

Is there a way to tell NHibernate.Linq to use the DistinctRootEntity transformer?

My query:

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

var feedItem = feedItemQuery.SingleOrDefault(); // This fails !?

The mapping:

<class name="FeedItem" table="FeedItems" proxy="IFeedItem">
    <id name="Id" type="Guid">
     <generator class="guid.comb"></generator>
    </id>
 ...
    <set name="Ads" table="Ads">
     <key column="FeedItemId" />
     <one-to-many class="Ad" />
    </set>
</class>

Thanks in advance,

Remco

Answer 1

var feedItemQuery = from ad in session.Linq().Expand("Ads")
where ad.Id == Id
select ad**.FirstOrDefault();**

Answer 2

You can use the RegisterCustomAction method to set the result transformer:

var linqsession = session.Linq<FeedItem>();
linqsession.QueryOptions.RegisterCustomAction(c => c.SetResultTransformer(new DistinctRootEntityResultTransformer()));
var feedItemQuery = from ad in linqsession.Expand("Ads")
                    where ad.Id == Id
                    select ad