I wanted to find out whether this is an NHibernate issue, or a LINQ issue
before posting it as an issue in JIRA. This issue only occurs in VB.Net.
When running any query containing a nullable type in the where clause, an
exception is thrown. For example:
Dim data = (From t In _session.Query(Of Table)()
Where t.IntegerField = 123).ToList()
Where IntegerField is a nullable integer, throws:
Unable to cast object of type 'NHibernate.Hql.Ast.HqlCoalesce' to type
'NHibernate.Hql.Ast.HqlBooleanExpression'.
The problem stems from the LINQ expression that is generated, in VB the
where clause generates:
.Where(t => ((t.IntegerField == ConvertChecked(123)) ?? False))
Whereas in C# the equivalent querys where clause generates:
.Where(t => (t.IntegerField == Convert(123)))
Interestingly, if I use the alternative syntax:
Dim data = (From t In _session.Query(Of Table)()).Where(Function(t)
(t.IntegerField = 123)).ToList()
the expression generated is:
.Where(t => Convert((t.IntegerField == ConvertChecked(123))))
Which works fine.
Someone else has raised this as an issue before (possibly with a better
description!) here:
http://stackoverflow.com/questions/9518058/nhibernate-linq-error-querying-when-nullable-types-in-where-clause
Is this something that could / should be fixed in NHibernate or is it more
of a VB LINQ compiler issue? Obviously we can work around it but it does
make our code unnecessarily complex.
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