NHibernate property mapping: columns and formula - nhibernate

Question

When i map columns from the inspected table, i do this:
<property name="InstanceName" type="MyNameUserType, MyApp.MyNamespace">
<column name="Name"/>
<column name="Name2"/>
</property>
How can I make property mapping initialize a UserType with data retrieved by the formula's sql query?
<property name="InstanceName" type="MyNameUserType, MyApp.MyNamespace" formula="(...)"/>
fails with an exception "wrong number of columns".
Thanks in advance!

Answer 1

MyUserNameType should be a class level mapping so that you can map the result of the SQL function to a class. See these two posts for some possible help:
Class and SQL Function example: http://thoughtspam.spaces.live.com/blog/cns!253515AE06513617!478.entry
NHibernate Mapping with formula mapping example:
http://thoughtspam.spaces.live.com/blog/cns!253515AE06513617!477.entry

Answer 2

I'm the author of the articles referenced by Michael. I had no idea people where still interested and I'm not sure it's applicable with the latest NHibernate.
Here's a fresh link though: http://thoughtspam.wordpress.com/2007/12/19/nhibernate-property-with-formula/
example, using Northwind...
Mapping:
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
<class name="PropertyFormulaExample.Shipper, PropertyFormulaExample" table="Shippers" lazy="false" >
<id name="ShipperID" column="ShipperID" unsaved-value="0">
<generator class="native" />
</id>
<property name="CompanyName" column="CompanyName" />
<property name="Phone" column="Phone" />
</class>
</hibernate-mapping>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
<class name="PropertyFormulaExample.Order, PropertyFormulaExample" table="Orders" lazy="false">
<id name="OrderID" column="OrderID" unsaved-value="0">
<generator class="native" />
</id>
<property name="CustomerID" column="CustomerID" />
<property name="ShipVia" type="PropertyFormulaExample.Shipper, PropertyFormulaExample" formula="dbo.GetShipper(shipvia)" />
</class>
</hibernate-mapping>
Entities:
public class Order
{
public int OrderID { get; set; }
public string CustomerID { get; set; }
public Shipper ShipVia { get; set; }
}
public class Shipper : ILifecycle
{
public int ShipperID { get; set; }
public string CompanyName { get; set; }
public string Phone { get; set; }
#region ILifecycle Members
public LifecycleVeto OnDelete(NHibernate.ISession s)
{
throw new NotImplementedException();
}
public void OnLoad(NHibernate.ISession s, object id)
{
}
public LifecycleVeto OnSave(NHibernate.ISession s)
{
throw new NotImplementedException();
}
public LifecycleVeto OnUpdate(NHibernate.ISession s)
{
throw new NotImplementedException();
}
#endregion
}
And finally the SQL function:
CREATE FUNCTION dbo.GetShipper(#shipperId int)
RETURNS int
AS
BEGIN
RETURN #shipperId
END
Obviously, you’ll want the function to do something meaningful, but the idea is you return the PK for the entity and implement ILifecycle.