Comparing ICompositeUserType objects in nHibernate

Question

I've made POCO object mapped to database like this:

class MoneyObject
{
    Money MoneyAmmount { get;set; }
    string Description { get;set; } 
}

MoneyAmmount - is type Money which is derived from ICompositeUserType and has 2 properties decimal Amount and string CurrencyCode:

class Money
{
    decimal Ammount { get;set; }
    string CurrencyCode { get;set; } 
}

Problem appears when I'm trying to fetch data from database using criteria, like following:

var criteria = session.CreateCriteria(typeof(MoneyObject))
    .Add(Expression.Lt("MoneyAmmount", money));

It generates following sql query:

SELECT this_.Id as Id2_0_, this_.Value as Value2_0_, this_.Currency as Currency2_0_, this_.Description as Descript4_2_0_ 
FROM MoneyObject this_ 
WHERE this_.Value < @p0 and this_.Currency < @p1;@p0 = 300,01, @p1 = 'USD'

I don't want to compare my valuetype object Money using CurrecyCode by character. I want to compare Money only by amount property and fetch data using criteria. But dealing in criteria only with properties of POCO object. Means I know that comparision works:

Expression.Lt("MoneyAmmount.Ammount", money.Ammount)

I want to avoid comparison by valuetype object properties and achieve comparison only between valuetype objects like

Expression.Lt("MoneyAmmount", money)

Does anybody know how to change such comparing behavior?

Answer 1

Try something like this

var criteria = session.CreateCriteria(typeof(MoneyObject), "m")
                             .CreateAlias("m.MoneyAmmount", "a")
                             .Add(Expression.Lt("a.Ammount", money));

Creating the aliases "m" and "a" lets you compare to the nested property.