Setting SqlDateTime.Null in a constructor

Question

How do I set a null value for an optional DateTime parameter in a constructor?

I'm using the following constructor below and I want the optional parameter admissionDate to be a null DateTime. Setting it to Nothing actually gives it a value (something like #12:00:00 #).

Public Sub New(ByVal obj1 as Object, Optional ByVal admissionDate As DateTime = System.Data.SqlTypes.SqlDateTime.Null)

Answer 1

I normally use DateTime.MinValue to represent a null date/time.

Answer 2

Have you tried DBNull.Value?

Answer 3

You'll need a Nullable DateTime. In C#, that's Nullable<DateTime> or DateTime?. I'm not sure of the VB.NET syntax, but I think it's something like Nullable(Of DateTime)

 Public Sub New(ByVal obj1 as Object, _
        Optional ByVal admissionDate As Nullable(Of DateTime) = Null)

Answer 4

System.Data.SqlTypes.SqlDateTime is not the same as builtin datetime.

You can use that type or use a nullable datetime.

Answer 5

I'd suggest using James Curran's solution but use Overloading instead of an optional parameter, as a workaround for the error you mentioned ("Optional parameters cannot have structure types") :

Public Sub New(ByVal obj1 As Object, ByVal admissionDate As Nullable(Of DateTime))
  //Your code here
End Sub

Public Sub New(Byval obj1 As Object)
  Me.New(obj1, Nothing)
End Sub

You can also use DateTime? instead of Nullable(Of DateTime) in the latest version of VB (not sure about the older versions).