NHibernate QueryOver projections - projecting collections to DTO

Question

I am trying to project a collection of an entity into a DTO. Easy enough with simple properties, but having an issue with collections:

public class Blog
{
   public string Name {get;set;}
   public IList<Comments> Comments {get;set;}
   //... more properties
}
public class Comments
{
   public Blog Blog {get;set;}
   //... more properties
}
public class MyDTO
{
   public string BlogName {get;set;}
   public IList<Comments> {get;set;}
}

Query goes a little something like:

var dto = _session.QueryOver<Blog>(() => blogAlias)
                            .JoinAlias(x => x.Comments, () => commentsAlias, JoinType.LeftOuterJoin)
                            .Select(
                                Projections.Property(() => blogAlias.Reference).WithAlias(() => myDTO.Reference),
                                // what project here to project blogAlias.Comments into myDTO.Comments))
                            .TransformUsing(Transformers.AliasToBean<MyDTO>()
                            .SingleOrDefault<MyDTO>();

EDIT UPDATE

I cannot seem to get a simple projection to run even without the transform and get: "Index was outside the bounds of the array":

  var dto = _session.QueryOver<Blog>(() => blogAlias)
                                .JoinAlias(x => x.Comments, () => commentsAlias, JoinType.LeftOuterJoin)
                                .Select(
                                    Projections.Property(() => blogAlias.Reference).WithAlias(() => myDTO.Reference),
Projections.Property(() => blogAlias.Comments).WithAlias(() => myDTO.Comments)
                                .List<object>();

try changin this: _session.QueryOver(() => blogAlias) .JoinAlias(() => blogAlias.Comments — Baz1nga, May 12 '12 at 21:16
Why was this closed as a duplicate when it clearly asks a different question? The linked issue deals with CriteriaQuery not QueryOver. — Michael Minton, Sep 21 '12 at 14:54
@Chev, a long time ago, but did you ever get an answer to this problem :-) — InitLipton, Sep 05 '19 at 16:17
@InitLipton sorry, but haven't used NHibernate for 6+ years and cannot actually recall — Samuel Goldenbaum, Oct 14 '19 at 21:09

score 6 · Answer 1 · answered May 10 '12 at 17:16

I am guessing this is what you should do..

Update your DTO to:

public class MyDTO
{
   public string BlogName {get;set;}
   public IList<Comments> Comments {get;set;}
}

Your modified query:

var dto = _session.QueryOver<Blog>(() => blogAlias)
          .JoinAlias(x => x.Comments, () => commentsAlias, JoinType.LeftOuterJoin)
          .Select(Projections.Property(() => blogAlias.Reference).WithAlias(() => myDTO.Reference),
                  Projections.Property(() => blogAlias.Comments).WithAlias(() => myDTO.Comments),
          .TransformUsing(Transformers.AliasToBean<MyDTO>()
          .SingleOrDefault<MyDTO>()

if that doesnt work then

_session.QueryOver<Blog>(() => blogAlias)
              .JoinAlias(x => x.Comments, () => commentsAlias, JoinType.LeftOuterJoin)
              .Select(Projections.Property(() => blogAlias.Reference),
                      Projections.Property(() => blogAlias.Comments))
              .SingleOrDefault<object[]>()
              .Select(x=>new MyDTO {BlogName=(string)x[0],Comments=x[1].Select(y=>y.ToString()).ToList())};

thanks for the reply, but I get "Index was outside the bounds of the array" when trying to use Projections.Property for the collection - even if I leave off the transform and just do a simple List — Samuel Goldenbaum, May 11 '12 at 11:41
no, check the updated edit in the question - running select then list — Samuel Goldenbaum, May 11 '12 at 12:56
thanks for the link - that deals with the DictinctResultsTransformer, I see the issue even when there are no transformers. — Samuel Goldenbaum, May 14 '12 at 05:12

NHibernate QueryOver projections - projecting collections to DTO

1 Answers1

Linked