Nullable(Of T) Structure

' This code example demonstrates the Nullable(Of T) class. 
' The code example defines a database table in which two columns  
' are nullable. In the application, an array of rows is created  
' and initialized. The table rows could subsequently be  
' written to a database. 

Imports System

Class Sample
    ' Define the "titleAuthor" table of the Microsoft "pubs" database.  

    Public Structure titleAuthor
    ' Author ID; format ###-##-#### 
        Public au_id As String 
    ' Title ID; format AA#### 
        Public title_id As String 
    ' Author ORD is nullable. 
        Public au_ord As Nullable(Of Short)
    ' Royalty Percent is nullable. 
        Public royaltyper As Nullable(Of Integer)
    End Structure 'titleAuthor

    Public Shared Sub Main() 
    ' Declare and initialize the titleAuthor array. 
        Dim ta(2) As titleAuthor
        ta(0).au_id = "712-32-1176"
        ta(0).title_id = "PS3333"
        ta(0).au_ord = 1
        ta(0).royaltyper = 100

        ta(1).au_id = "213-46-8915"
        ta(1).title_id = "BU1032"
        ta(1).au_ord = Nothing
        ta(1).royaltyper = Nothing

        ta(2).au_id = "672-71-3249"
        ta(2).title_id = "TC7777"
        ta(2).au_ord = Nothing
        ta(2).royaltyper = 40

    ' Display the values of the titleAuthor array elements, and  
    ' display a legend.
        Display("Title Authors Table", ta)
        Console.WriteLine("Legend:")
        Console.WriteLine("An Author ORD of -1 means no value is defined.")
        Console.WriteLine("A Royalty % of 0 means no value is defined.")
    End Sub 'Main

    ' Display the values of the titleAuthor array elements. 
    Public Shared Sub Display(ByVal dspTitle As String, _
                              ByVal dspAllTitleAuthors() As titleAuthor) 
        Console.WriteLine("*** {0} ***", dspTitle)
        Dim dspTA As titleAuthor
        For Each dspTA In dspAllTitleAuthors
            Console.WriteLine("Author ID ... {0}", dspTA.au_id)
            Console.WriteLine("Title ID .... {0}", dspTA.title_id)
            Console.WriteLine("Author ORD .. {0}", dspTA.au_ord.GetValueOrDefault(-1))
            Console.WriteLine("Royalty % ... {0}", dspTA.royaltyper.GetValueOrDefault(0))
            Console.WriteLine()
        Next dspTA
    End Sub 'Display
End Class 'Sample

' 
'This code example produces the following results: 
' 
'*** Title Authors Table *** 
'Author ID ... 712-32-1176 
'Title ID .... PS3333 
'Author ORD .. 1 
'Royalty % ... 100 
' 
'Author ID ... 213-46-8915 
'Title ID .... BU1032 
'Author ORD .. -1 
'Royalty % ... 0 
' 
'Author ID ... 672-71-3249 
'Title ID .... TC7777 
'Author ORD .. -1 
'Royalty % ... 40 
' 
'Legend: 
'An Author ORD of -1 means no value is defined. 
'A Royalty % of 0 means no value is defined. 
'