Question

I am try to convert the following NHibernate query using dyanmic instantiation into an IList<t> rather than an IList.

IList<AllName> allNames =
  (IList<AllName>)Session.CreateQuery(
  @"select new AllName(
  name.NameId, name.FirstName, origin.OriginId, origin.Description,
  name.Sex, name.Description, name.SoundEx
  ) from Name name join name.Origin origin")
  .SetFirstResult(skip)
  .SetMaxResults(pageSize);

Running this I get the following error:-

Unable to cast object of type
‘NHibernate.Impl.QueryImpl’ to type
‘System.Collections.Generic.IList`1[Domain.Model.Entities.AllName]’.

I know that I can return

IList results = Sesssion.CreateQuery(...

but my service layers expect an

IList<AllName>

How can I achieve this?

Answer 1

One option would be to write an IList<T> implementation which proxies to an IList, casting where appropriate. It shouldn’t be too hard to do, albeit somewhat tedious. LINQ will make this slightly easier in terms of implementing IEnumerable<T> etc – you can just call the underlying iterator and call Cast<T>() on it, for example.

Another solution would be to create a new List<T> from the returned list:

IList query = Session.CreateQuery(...);
IList<AllName> allNames = new List<AllName>(query.Cast<AllName>());

EDIT: As Sander so rightly points out, this is what ToList is for:

IList query = Session.CreateQuery(...);
return query.Cast<AllName>().ToList();

EDIT: All of this has been NHibernate-agnostic, as it were – I don’t actually know much about NHibernate. Rippo has now found a much simpler answer – call List<AllName> instead (which is an NHibernate method).