.Cacheable().Fetch() throws 'Exception occurred getter of xxx'

Segura, Eduardo [Tech]

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Aug 17, 2010, 1:28:33 PM8/17/10

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I’m wondering if this is the right way to use second-level caching along with eagerly loading a collection.

This code is equivalent to a query that we are issuing from a fairly large application. I’ve stripped it down to the very minimum while still throwing the exception.

(My apologies for the rather large email, but I want to provide as much information up-front as possible)

I have this test set up:

[TestMethod]

public void FindWithFetchAndCacheableTest()

{

IPersistenceService ps = PersistenceServiceFactory.CreateService(PersistenceServiceType.Hibernate);

IList<ParentObject> pos = ps.Find<ParentObject, IQueryable<ParentObject>>(ParentObjects =>

from po in ParentObjects

select po)

.Cacheable()

.Fetch(po => po.ChildObjects).ToList();

Assert.IsTrue(pos.Count > 0);

}

My uneducated guess:

--------------------------------------

The lambda expression in Fetch() is being used as a ‘resultTransfomer’ here:

(NHibernate.Hql.Ast.ANTLR.Loader.QueryLoader.cs:line 335, using NH3.0.0Alpha1)

protected override object GetResultColumnOrRow(object[] row, IResultTransformer resultTransformer, IDataReader rs,

ISessionImplementor session)

{

row = ToResultRow(row); <-- after this assignment, row is an Array[1] holding my object

bool hasTransform = HasSelectNew || resultTransformer != null; <-- at this point, resultTransformer has a lambda

…

else if (!hasTransform)

{

return row.Length == 1 ? row[0] : row; <-- the object is not extracted from the array, because of the lambda

}

And this method ends up returning an array (object[1] = [{ ParentObject}]), instead of returning the object itself.

Then later on, since the ‘object[1]’ array doesn’t have an ‘Id’ property, this line throws the exception:

(NHibernate.Properties.BasicPropertyAccessor.cs:Line 207 (BasicGetter.Get)):

public object Get(object target)

{

try

{

return property.GetValue(target, new object[0]); <-- target is not {ParentObject}, but an object[1] instead

}

catch (Exception e)

{

throw new PropertyAccessException(e, "Exception occurred", false, clazz, propertyName);

}

My classes:

------------------------------------------------------

public class ParentObject

{

public virtual int Id { get; set; }

public virtual string Name { get; set; }

public virtual ISet<ChildObject> ChildObjects { get; set; }

public virtual void AddChildObject(ChildObject co)

{

this.ChildObjects.Add(co);

co.Parent = this;

}

public class ChildObject

{

public virtual int Id { get; set; }

public virtual string Name { get; set; }

public virtual ParentObject Parent { get; set; }

}

Mappings:

----------------------------------------

<?xml version="1.0" encoding="utf-8" ?>

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" auto-import="true">

</id>

<one-to-many class="PersistenceLayer.Test.Model.ChildObject"/>

</set>

</class>

</hibernate-mapping>

<?xml version="1.0" encoding="utf-8" ?>

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" auto-import="true">

</id>

<many-to-one name="Parent" column="ParentId" not-null="true"/>

</class>

</hibernate-mapping>

But it throws this exception:

Test method PersistenceLayer.Test.PersistenceServiceTest.FindWithFetchAndCacheableTest threw exception: NHibernate.PropertyAccessException: Exception occurred getter of PersistenceLayer.Test.Model.ParentObject.Id ---> System.Reflection.TargetException: Object does not match target type..

System.Reflection.RuntimeMethodInfo.CheckConsistency(Object target)

System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks)

System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)

System.Reflection.RuntimePropertyInfo.GetValue(Object obj, BindingFlags invokeAttr, Binder binder, Object[] index, CultureInfo culture)

System.Reflection.RuntimePropertyInfo.GetValue(Object obj, Object[] index)

NHibernate.Properties.BasicPropertyAccessor.BasicGetter.Get(Object target) in d:\CSharp\NH\nhibernate\src\NHibernate\Properties\BasicPropertyAccessor.cs: line 207

NHibernate.Properties.BasicPropertyAccessor.BasicGetter.Get(Object target) in d:\CSharp\NH\nhibernate\src\NHibernate\Properties\BasicPropertyAccessor.cs: line 211

NHibernate.Tuple.Entity.AbstractEntityTuplizer.GetIdentifier(Object entity) in d:\CSharp\NH\nhibernate\src\NHibernate\Tuple\Entity\AbstractEntityTuplizer.cs: line 139

NHibernate.Persister.Entity.AbstractEntityPersister.GetIdentifier(Object obj, EntityMode entityMode) in d:\CSharp\NH\nhibernate\src\NHibernate\Persister\Entity\AbstractEntityPersister.cs: line 3838

NHibernate.Persister.Entity.AbstractEntityPersister.IsTransient(Object entity, ISessionImplementor session) in d:\CSharp\NH\nhibernate\src\NHibernate\Persister\Entity\AbstractEntityPersister.cs: line 3629

NHibernate.Engine.ForeignKeys.IsTransient(String entityName, Object entity, Nullable`1 assumed, ISessionImplementor session) in d:\CSharp\NH\nhibernate\src\NHibernate\Engine\ForeignKeys.cs: line 193

NHibernate.Engine.ForeignKeys.GetEntityIdentifierIfNotUnsaved(String entityName, Object entity, ISessionImplementor session) in d:\CSharp\NH\nhibernate\src\NHibernate\Engine\ForeignKeys.cs: line 249

NHibernate.Type.ManyToOneType.Disassemble(Object value, ISessionImplementor session, Object owner) in d:\CSharp\NH\nhibernate\src\NHibernate\Type\ManyToOneType.cs: line 137

NHibernate.Cache.StandardQueryCache.Put(QueryKey key, ICacheAssembler[] returnTypes, IList result, Boolean isNaturalKeyLookup, ISessionImplementor session) in d:\CSharp\NH\nhibernate\src\NHibernate\Cache\StandardQueryCache.cs: line 82

NHibernate.Loader.Loader.PutResultInQueryCache(ISessionImplementor session, QueryParameters queryParameters, IType[] resultTypes, IQueryCache queryCache, QueryKey key, IList result) in d:\CSharp\NH\nhibernate\src\NHibernate\Loader\Loader.cs: line 1627

NHibernate.Loader.Loader.ListUsingQueryCache(ISessionImplementor session, QueryParameters queryParameters, ISet`1 querySpaces, IType[] resultTypes) in d:\CSharp\NH\nhibernate\src\NHibernate\Loader\Loader.cs: line 1593

NHibernate.Loader.Loader.List(ISessionImplementor session, QueryParameters queryParameters, ISet`1 querySpaces, IType[] resultTypes) in d:\CSharp\NH\nhibernate\src\NHibernate\Loader\Loader.cs: line 1567

NHibernate.Hql.Ast.ANTLR.Loader.QueryLoader.List(ISessionImplementor session, QueryParameters queryParameters) in d:\CSharp\NH\nhibernate\src\NHibernate\Hql\Ast\ANTLR\Loader\QueryLoader.cs: line 298

NHibernate.Hql.Ast.ANTLR.QueryTranslatorImpl.List(ISessionImplementor session, QueryParameters queryParameters) in d:\CSharp\NH\nhibernate\src\NHibernate\Hql\Ast\ANTLR\QueryTranslatorImpl.cs: line 110

NHibernate.Engine.Query.HQLQueryPlan.PerformList(QueryParameters queryParameters, ISessionImplementor session, IList results) in d:\CSharp\NH\nhibernate\src\NHibernate\Engine\Query\HQLQueryPlan.cs: line 105

NHibernate.Impl.SessionImpl.List(IQueryExpression queryExpression, QueryParameters queryParameters, IList results) in d:\CSharp\NH\nhibernate\src\NHibernate\Impl\SessionImpl.cs: line 679

NHibernate.Impl.SessionImpl.List(IQueryExpression queryExpression, QueryParameters parameters) in d:\CSharp\NH\nhibernate\src\NHibernate\Impl\SessionImpl.cs: line 655

NHibernate.Impl.ExpressionQueryImpl.List() in d:\CSharp\NH\nhibernate\src\NHibernate\Impl\ExpressionQueryImpl.cs: line 63

NHibernate.Linq.NhQueryProvider.Execute(Expression expression) in d:\CSharp\NH\nhibernate\src\NHibernate\Linq\NhQueryProvider.cs: line 31

NHibernate.Linq.NhQueryProvider.Execute[TResult](Expression expression) in d:\CSharp\NH\nhibernate\src\NHibernate\Linq\NhQueryProvider.cs: line 55

GetEnumerator()

ctor(IEnumerable`1 collection)

System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)

PersistenceLayer.Test.PersistenceServiceTest.FindWithFetchAndCacheableTest() in …..\PersistenceServiceTest.cs: line 345

Thanks,

Eduardo

Segura, Eduardo [Tech]

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Aug 19, 2010, 10:08:33 AM8/19/10

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Hi folks,

Could I get your feedback on this one? Am I missing something?

Thanks,

Diego Mijelshon

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Aug 19, 2010, 10:28:16 AM8/19/10

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Well, I don't know what the code of

IPersistenceService.Find does, but the following works here:

  session.Query<Foo>().Cacheable().Fetch(f => f.Bar).ToList();

And I don't get the idea behind "from po in ParentObjects select po"; that's a noop.

Diego

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Segura, Eduardo [Tech]

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Aug 19, 2010, 10:38:09 AM8/19/10

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Hi Diego,

Are you running off of the trunk? Because this still throws that exception with Alpha1:

IList<ParentObject> pos =

session.Query<ParentObject>().Cacheable().Fetch(po => po.ChildObjects).ToList();

Thanks,

Eduardo

Diego Mijelshon

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Aug 19, 2010, 11:02:34 AM8/19/10

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Alpha2.

I don't see it caching the query, though... but it returns the correct records.

Diego

Segura, Eduardo [Tech]

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Aug 19, 2010, 4:20:33 PM8/19/10

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Actually, Alpha2 is also throwing for me. I’m attaching the new stack trace so you can verify that I’m using Alpha2 (the line numbers for the stack vary slightly, reflecting what has been committed to the trunk since Alpha1).

I’ve also updated my little test, just to check if the fact that you are not eagerly fetching a collection, but just a single object, ‘Bar’:

  session.Query<Foo>().Cacheable().Fetch(f => f.Bar).ToList();

could be what’s causing this, but unfortunately the result is the same for me:

// this line is ok

IList<ParentObject> pos2 = session.Query<ParentObject>().Cacheable().ToList();

// this line is ok

IList<ChildObject> cos2 = session.Query<ChildObject>().Cacheable().ToList();

// this throws with Alpha2

IList<ChildObject> cos = session.Query<ChildObject>()

.Cacheable()

.Fetch(co => co.Parent).ToList();

// this throws with Alpha2

IList<ParentObject> pos = session.Query<ParentObject>()

.Cacheable()

.Fetch(po => po.ChildObjects).ToList();

I did see the behavior you describe, ‘don't see it caching the query’, but only briefly, just before rebuilding the whole project. (I’m using memcached, and since there is no NHContrib for Alpha2 yet, after a rebuild I started getting errors regarding not being able to load 3.0.0.1001, so I removed the reference and started using HashtableCache instead).

So, I’m wondering if maybe this is what happened for you as well. Could you confirm?

Eduardo

Stack trace:

---------------