[nhibernate-issues] [JIRA] Created: (NH-1344) QueryTranslator: Invalid Cast to object array when using IResultTransformer

[NHibernate J. <nh...@gm...>]

QueryTranslator: Invalid Cast to object array when using IResultTransformer
---------------------------------------------------------------------------

                 Key: NH-1344
                 URL: http://jira.nhibernate.org/browse/NH-1344
             Project: NHibernate
          Issue Type: Patch
          Components: Core
    Affects Versions: 2.0.0.Alpha1, 1.2.1, 1.2.0.GA, 2.0.0.Alpha2, 2.0.0.GA
            Reporter: Stefan Simroth
            Priority: Minor
         Attachments: QueryTranslatorInvalidCastToObjectArray20trunk.patch

there seems to be an issue with a hard cast in the QueryTranslator
class, line 1452 (trunk) - resp. line 1288 (1.2.1) ...

The hard cast in method GetResultList to an object[] fails in the case
of my company's product, when using an IResultTransformer.

I chose to use an IResultTransformer implementation for Criteria's and
Query's to be able to set a required property. It seems an appropriate
way to me and my tests (and the running app) ensure that it works.

However, I had to patch the QueryTranslator at the locations mentioned
above, because it threw an invalid cast exception (stacktrace below) -
because the IList of my objects could not be casted to an object[].
Debugging it, showed me that the "results" list contained my domain
objects, but it could not be casted to an object[]. It was a collection
of my domain types and my domain types are no object[]. Now, some time
passed by since then, and our product works fine with the patch, so
unfortunately I forgot the exact reason, but I'd guess, I used the
generic Query signature and so the results list was a generic list that
cannot be casted to object[]. But also ArrayList or Hashtable cannot be
casted to object[]...

A little experiment, gave me the compiler error:

Cannot convert type
'System.Collections.Generic.List<ConsoleApplication1.Project>' to 'object[]'

class Program
{
        static void Main(string[] args)
        {
                List<Project> projects = new List<Project>();
                object[] objs = (object[]) projects;
        }

        class Project { }

}

=> same thing doesn't work with ArrayList or Hashtable ...

----
The code snippet from QueryTranslator in question:

        for (int i = 0; i < results.Count; i++)
        {
                object[] row = (object[]) results[i];
                results[i] = holderInstantiator.Instantiate(row);
        }

----
Patch - with a "safe" cast:

        object[] row = results[i] as object[];
        if (row != null)
        {
                results[i] = holderInstantiator.Instantiate(row);
        }

The included patch is for the NHibernate 2.0 trunk.
The same problem exists in earlier versions, namely 1.2.

I might be totally missing the root of the problem, but please excuse
this, as I am not familiar with the NHibernate internals, but tried to
apply a patch at the right place to enable the very useful feature of
the IResultTransformer to our case - and maybe to others in future.

Here is the stacktrace:  (version 1.2.1)

    at NHibernate.Hql.Classic.QueryTranslator.GetResultList(IList
results, IResultTransformer resultTransformer) in
d:\dev\yap\nhibernate\trunk\src\NHibernate\Hql\Classic\QueryTranslator.cs:line
1291
    at NHibernate.Loader.Loader.ListIgnoreQueryCache(ISessionImplementor
session, QueryParameters queryParameters) in
d:\dev\yap\nhibernate\trunk\src\NHibernate\Loader\Loader.cs:line 1744
    at NHibernate.Loader.Loader.List(ISessionImplementor session,
QueryParameters queryParameters, ISet querySpaces, IType[] resultTypes)
in d:\dev\yap\nhibernate\trunk\src\NHibernate\Loader\Loader.cs:line 1738
    at NHibernate.Hql.Classic.QueryTranslator.List(ISessionImplementor
session, QueryParameters queryParameters) in
d:\dev\yap\nhibernate\trunk\src\NHibernate\Hql\Classic\QueryTranslator.cs:line
1124
    at NHibernate.Impl.SessionImpl.Find(String query, QueryParameters
parameters, IList results) in
d:\dev\yap\nhibernate\trunk\src\NHibernate\Impl\SessionImpl.cs:line 1763 

----

My IResultTransformer implementation:

  #region IResultTransformer Members

   public object TransformTuple(object[] tuple, string[] aliases)
   {
    object o = CriteriaUtil.RootEntity.TransformTuple(tuple, aliases);
    TrySetDomainModelStore(o);
    return o;
   }

   public IList TransformList(IList collection)
   {
    for (int i = 0; i < collection.Count; i++)
    {
     TrySetDomainModelStore(collection[i]);
    }
    return collection;
   }

   #endregion

TranformTuple is called rarely. TransformList is called after the
HolderInstantiator call.

I never create a new MyEntity[] { my, domain, entities}, nor a new
object[] { my, domain, entities} ... 

------ 	 	
Felix Gartsman:   	
Isn't this similar to Hibernate issues:
http://opensource.atlassian.com/projects/hibernate/browse/HHH-2463
http://opensource.atlassian.com/projects/hibernate/browse/HHH-2525
They are also present in NH, and they prevent caching queries with
IResultTransformer - the caching thinks it gets a tuple, but it's actually
the transformed object. 


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