Re: Patch for QueryTranslator Invalid Cast to object array

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.


From: [email protected]
[mailto:[email protected]] On Behalf Of
Ayende Rahien
Sent: Wednesday, June 11, 2008 1:52 PM
To: the NHibernate development list
Subject: Re: [NHibernate-development] Patch for QueryTranslator Invalid Cast
to object array

The problem is with your IResultTransformer class.
You need to create a new object[] { my, domain, entities}, instead of new
MyEntity[] { my, domain, entities}
On Wed, Jun 11, 2008 at 11:51 AM, Stefan Simroth <[email protected]> wrote:
Hello NHibernate developers,

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:li
ne 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:li
ne 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



Hope to could have helped a bit ...
Nevertheless, big thanx for such a great software!

... best regards,

Stefan


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Index: QueryTranslator.cs
===================================================================
--- QueryTranslator.cs  (revision 3539)
+++ QueryTranslator.cs  (working copy)
@@ -1449,8 +1449,11 @@
                       {
                               for (int i = 0; i < results.Count; i++)
                               {
-                                       object[] row = (object[])
results[i];
-                                       results[i] =
holderInstantiator.Instantiate(row);
+                                       object[] row = results[i] as
object[];
+                                       if (row != null)
+                                       {
+                                               results[i] =
holderInstantiator.Instantiate(row);
+                                       }
                               }

                               if (holderConstructor == null &&
resultTransformer != null)

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