NHibernate 3CR1: Fetching strategy problems - nhibernate

Question

Continuation to the previous question, I tried to avoid the problem another way:
Just for the reminder:
My database schema is described below:
Form <-> Log
<--->>Seller1
<--->>Seller2
<--->>Seller3
I have a major entity (Form), one to
one relationship to another object
(Log) And one to many relationship to
the childs (Sellers).
I want to pull out all the Forms that
one of their Sellers meets certain
conditions.
I tried like this now:
[Test]
public void Can_Get_Forms_Where_CorporationNumber_Is_510778087_Metohd1()
{
var CorporationNumber = "513514950";
var list1 = sellerRepository
.Where(x => x.CorporationNumber == CorporationNumber)
.Select(x => x.Form)
.Fetch(x => x.Log)
.Take(10).ToList();
CollectionAssert.IsNotEmpty(list1);
}
But unfortunately I get NullReferenceException:
TestUsingDevelopmentDataBase.Moch.BillOfSale.Data.FormRepositoryTests.Can_Get_Forms_Where_CorporationNumber_Is_510778087_Metohd1:
System.NullReferenceException : Object
reference not set to an instance of an
object
EDIT: stacktrace:
at
NHibernate.Linq.Visitors.ResultOperatorProcessors.ProcessFetch.Process(FetchRequestBase
resultOperator, QueryModelVisitor
queryModelVisitor, IntermediateHqlTree
tree) in
d:\CSharp\NH\nhibernate\src\NHibernate\Linq\Visitors\ResultOperatorProcessors\ProcessFetch.cs:line
11 at
NHibernate.Linq.Visitors.ResultOperatorProcessors.ProcessFetchOne.Process(FetchOneRequest
resultOperator, QueryModelVisitor
queryModelVisitor, IntermediateHqlTree
tree) in
d:\CSharp\NH\nhibernate\src\NHibernate\Linq\Visitors\ResultOperatorProcessors\ProcessFetchOne.cs:line
9 at
NHibernate.Linq.Visitors.ResultOperatorProcessors.ResultOperatorProcessor1.Process(ResultOperatorBase
resultOperator, QueryModelVisitor
queryModel, IntermediateHqlTree tree)
in
d:\CSharp\NH\nhibernate\src\NHibernate\Linq\Visitors\ResultOperatorProcessors\ResultOperatorProcessor.cs:line
17 at
NHibernate.Linq.Visitors.ResultOperatorProcessors.ResultOperatorMap.Process(ResultOperatorBase
resultOperator, QueryModelVisitor
queryModel, IntermediateHqlTree tree)
in
d:\CSharp\NH\nhibernate\src\NHibernate\Linq\Visitors\ResultOperatorProcessors\ResultOperatorMap.cs:line
24 at
NHibernate.Linq.Visitors.QueryModelVisitor.VisitResultOperator(ResultOperatorBase
resultOperator, QueryModel queryModel,
Int32 index) in
d:\CSharp\NH\nhibernate\src\NHibernate\Linq\Visitors\QueryModelVisitor.cs:line
125 at
Remotion.Data.Linq.Clauses.ResultOperatorBase.Accept(IQueryModelVisitor
visitor, QueryModel queryModel, Int32
index) at
Remotion.Data.Linq.QueryModelVisitorBase.VisitResultOperators(ObservableCollection1
resultOperators, QueryModel
queryModel) at
Remotion.Data.Linq.QueryModelVisitorBase.VisitQueryModel(QueryModel
queryModel) at
NHibernate.Linq.Visitors.QueryModelVisitor.Visit()
in
d:\CSharp\NH\nhibernate\src\NHibernate\Linq\Visitors\QueryModelVisitor.cs:line
96 at
NHibernate.Linq.Visitors.QueryModelVisitor.GenerateHqlQuery(QueryModel
queryModel, VisitorParameters
parameters, Boolean root) in
d:\CSharp\NH\nhibernate\src\NHibernate\Linq\Visitors\QueryModelVisitor.cs:line
49 at
NHibernate.Linq.NhLinqExpression.Translate(ISessionFactoryImplementor
sessionFactory) in
d:\CSharp\NH\nhibernate\src\NHibernate\Linq\NhLinqExpression.cs:line
67 at
NHibernate.Hql.Ast.ANTLR.ASTQueryTranslatorFactory.CreateQueryTranslators(String
queryIdentifier, IQueryExpression
queryExpression, String
collectionRole, Boolean shallow,
IDictionary2 filters,
ISessionFactoryImplementor factory) in
d:\CSharp\NH\nhibernate\src\NHibernate\Hql\Ast\ANTLR\ASTQueryTranslatorFactory.cs:line
27 at
NHibernate.Engine.Query.HQLExpressionQueryPlan.CreateTranslators(String
expressionStr, IQueryExpression
queryExpression, String
collectionRole, Boolean shallow,
IDictionary2 enabledFilters,
ISessionFactoryImplementor factory) in
d:\CSharp\NH\nhibernate\src\NHibernate\Engine\Query\HQLExpressionQueryPlan.cs:line
34 at
NHibernate.Engine.Query.HQLExpressionQueryPlan..ctor(String
expressionStr, IQueryExpression
queryExpression, String
collectionRole, Boolean shallow,
IDictionary2 enabledFilters,
ISessionFactoryImplementor factory) in
d:\CSharp\NH\nhibernate\src\NHibernate\Engine\Query\HQLExpressionQueryPlan.cs:line
23 at
NHibernate.Engine.Query.HQLExpressionQueryPlan..ctor(String
expressionStr, IQueryExpression
queryExpression, Boolean shallow,
IDictionary2 enabledFilters,
ISessionFactoryImplementor factory) in
d:\CSharp\NH\nhibernate\src\NHibernate\Engine\Query\HQLExpressionQueryPlan.cs:line
17 at
NHibernate.Engine.Query.QueryPlanCache.GetHQLQueryPlan(IQueryExpression
queryExpression, Boolean shallow,
IDictionary2 enabledFilters) in
d:\CSharp\NH\nhibernate\src\NHibernate\Engine\Query\QueryPlanCache.cs:line
88 at
NHibernate.Impl.AbstractSessionImpl.GetHQLQueryPlan(IQueryExpression
queryExpression, Boolean shallow) in
d:\CSharp\NH\nhibernate\src\NHibernate\Impl\AbstractSessionImpl.cs:line
302 at
NHibernate.Impl.AbstractSessionImpl.CreateQuery(IQueryExpression
queryExpression) in
d:\CSharp\NH\nhibernate\src\NHibernate\Impl\AbstractSessionImpl.cs:line
258 at
NHibernate.Linq.NhQueryProvider.PrepareQuery(Expression
expression, IQuery& query,
NhLinqExpression& nhQuery) in
d:\CSharp\NH\nhibernate\src\NHibernate\Linq\NhQueryProvider.cs:line
42 at
NHibernate.Linq.NhQueryProvider.Execute(Expression
expression) in
d:\CSharp\NH\nhibernate\src\NHibernate\Linq\NhQueryProvider.cs:line
25 at
NHibernate.Linq.NhQueryProvider.Execute[TResult](Expression
expression) in
d:\CSharp\NH\nhibernate\src\NHibernate\Linq\NhQueryProvider.cs:line
102 at
Remotion.Data.Linq.QueryableBase1.GetEnumerator()
at
System.Collections.Generic.List1..ctor(IEnumerable1
collection) at
System.Linq.Enumerable.ToList[TSource](IEnumerable`1
source) at
TestUsingDevelopmentDataBase.Moch.BillOfSale.Data.FormRepositoryTests.Can_Get_Forms_Where_CorporationNumber_Is_510778087_Metohd1()
in
D:\Dev\NCommon\Moch.BillOfSale\Moch.BillOfSale.NHibenate.Tests\FormRepositoryTests.cs:line
207
The problem could be circumvented in a less well, as follows:
[Test]
public void Can_Get_Forms_Where_CorporationNumber_Is_510778087_Metohd2()
{
var CorporationNumber = "513514950";
var list2 = sellerRepository
.Where(x => x.CorporationNumber == CorporationNumber)
.Fetch(x => x.Form).ThenFetch(x => x.Log)
.Take(10).ToList().Select(x => x.Form);
CollectionAssert.IsNotEmpty(list2);
}
But of course we all prefer the elegant way and want to understand what lies behind the problem

Answer 1

I think Nhibernate doesn't like you fetching after a select. I ran into a null reference exception just like you did.
See my question here about it.
In Linq-to-Nhibernate, is it possible to use .Fetch() after a .Select()?
You might be able to .Select(x => x.Form) after your fetching in your second example before you .ToList() it, too.
I'm using Nhibernate 3.2 and this is still an issue. There should be a proper 'you can't fetch after a select' exception or something to spare us some pain.