Nhibernate Linq Sum与计算导致NotSupportedException

Question

I am using Nhibernate 3.3.3.4001 with SybaseSQLAnywhere12Dialect and trying to use a simple calculation within a sum linq function.

I would like to use Linq rather than HQL to achieve this and would be happy to extend Nhibernate with a default linq to hql generator.

Using the following Linq query raises the exception

System.NotSupportedException: Expression type 'NhSumExpression' is not supported by this SelectClauseVisitor

Linq Query

var query = (from c in session.Query<Entity>()
            select c.FieldValue / 100M).Sum()

Expected SQL Statement

SELECT SUM(FieldValue / 100.0) FROM TableName

If the same query is run without the Sum() function it performs the calculation correctly, as such am confused why the Sum() wouldn't work.

Answer 1

You may try to rewrite your LINQ query a bit, just like this one:

var result = ((from c in session.Query<Entity>()
               select c.FieldValue).Sum()) / 100;

Resulting query could also be optimized by moving division operator out of the sum:

SELECT SUM(FieldValue) / 100 FROM TableName

Answer 2

There is an open issue when using constants within Linq group function (Max, Min, Sum) functions. If another field is used it will work correctly.

Found bug within NHibernate 3.3.3
https://nhibernate.jira.com/browse/NH-3376