I'm writing a macro that will populate a property with a property expression

Example: Custom Property "Material" = "SW-Material@Part2.SLDPRT"

Notice that the file is called "Part2.SLDPRT" because it is new and have not been saved.

From an API call, how do I get the value "Part2.SLDPRT"?  Modeldoc.getpathname() will give empty string ""

If the user saves the file, my code will work because getpathname has a value.  Do I have to make the user save first?  If so, why.  The use could do this through the interface and get the right value because SolidWorks "Knows" that the part is called Part2.SLDPRT".  Does the API expose this?

Here is the basic code

Public Sub main()

     Dim swModel As ModelDoc2

     swModel = swApp.ActiveDoc

     Dim strDocName As String = swModel.GetPathName

     Dim CheckWeight As String = """SW-Mass@" & strDocName & """"

     swModel.CustomInfo2("", "Weight") = CheckWeight

End Sub

How do I make this work if the file is new and not saved yet?

Kent