NHibernate.Linq-Where子句中的Nullable类型时查询错误

Question

I have the following NHibernate Linq query:

From eachLine In myNhSession.Query(Of SamplePoco)()
     Where eachLine.SampleIntField = 1234

The property SamplePoco.SampleIntField is type Nullable(Of Int32)

When I run the query, I get the following exception:

System.InvalidCastException: Unable to cast object of type 'NHibernate.Hql.Ast.HqlCoalesce' to type 'NHibernate.Hql.Ast.HqlBooleanExpression'

If I change the property type to Int32 , it works. It seems that Nullable types are automatically converted into a coalesce expression by the Linq compiler.

Debugging the NHibernate, I just found out that this Where clause was converted into: {where ((eachLine.SampleIntField == 1234) ?? False)} . As I can understand, the whole condition comparison was translated to be coalesced instead of just the Nullable property.

If I put this way eachLine.SampleIntField.Equals(1234) it doesn't work as well ('Equals not implemented' exception)

If I change the query to the following code, it works:

From eachLine In myNhSession(Of SamplePoco)()
     Where {1234}.Contains(eachLine.SampleIntField)

(not elegant)

Another code that works as well (coalescing the field properly as I was expecting by the first query):

From eachLine In myNhSession(Of SamplePoco)()
 Where If(eachLine.SampleIntField,0) = 1234

Any suggestions to keep it simple?

Answer 1

I think the most explicitly clear way to put it, that NHibernate handles, is:

From eachLine In myNhSession.Query(Of SamplePoco)()
     Where eachLine.SampleIntField.HasValue AndAlso eachLine.SampleIntField.Value = 1234