cannot project entities in Linq 2 NHibernate

Question

I'm working with NHibernate 2 in a .Net project and I'm using the Linq2NHibernate provider. This simple query

var result = from d in session.Linq<Document>()
where d.CreationYear == 2010
select d.ChildEntity).ToList();

throws an exception telling me that is impossible to cast ChildEntity type do Document type. Why is that? I also tried to translate it in query methods, having

session.Linq<Document>()
   .where(d=>d.CreationYear == 2010)
   .select(d=>d.ChildEntity)
   .ToList();

Isn't the select method supposed to project an IQueryble into a IQueryble, beeing TResult!=T ?

score 1 · Answer 1 · answered Mar 22 '12 at 12:00

Try this:

   var result = (from d in session.Linq<Document>()
   where d.CreationYear == 2010
   select new ChildEntityType
     { /* here just do a simple assignments for all ChildEntityType fields
          d.ChildEntity */ } ).ToList();

Yes, this could look quite stupid, but linq2nhibernate sometimes behave very strange, when you try to select just an object.

score 0 · Answer 2 · answered Jan 04 '12 at 11:46

0

can you try this:

session.Linq<Document>()
   .Where(d=>d.CreationYear == 2010)
   .Select(d=>d.ChildEntity)
   .ToList<T>();     //where T is typeof(ChildEntity)

answered Jan 04 '12 at 11:46

Baz1nga

15,485
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shouldn't be able to infer the return type for the select method without explicitly declare it? – themarcuz Jan 04 '12 at 14:48

score 0 · Accepted Answer · answered Jan 04 '12 at 15:03

0

The old Linq provider is extremely limited and has been unmaintained for several years.

I suggest that you upgrade to the latest stable NHibernate (3.2), which has a much better (and integrated) Linq provider.

answered Jan 04 '12 at 15:03

Diego Mijelshon

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too bad, I'm working on an old project and I cannot change the NHibernate version used. – themarcuz Jan 04 '12 at 15:12
1

You won't be able to use Linq for this query then. Use HQL instead. – Diego Mijelshon Jan 04 '12 at 15:17

cannot project entities in Linq 2 NHibernate

3 Answers3