How to check if DataReader value is not null?

Question

I\'m writing a VB.Net code that reads an Oracle Table through an SQL query.

The SQL query may return some null columns. I\'m trying to check if these columns are nul

Answer 1

Using Generic function with extension, will make it easier.

Imports System.Runtime.CompilerServices


Public Module DataReaderExtensions
  Public Function GetValue(Of T)(ByVal drVar As Object) As T
    If drVar.Equals(DBNull.Value) Then
        ' Value is null, determine the return type for a default
        If GetType(T).Equals(GetType(String)) Then
            Return CType(CType("", Object), T)
        Else
            ' If it's anything else just return nothing
            Return CType(Nothing, T)
        End If
    Else
        ' Cast the value into the correct return type
        Return CType(drVar, T)
    End If
  End Function
End Module

And you can call it like

dr.Item("abc").GetValue(string)
dr.Item("def").GetValue(Nullable(of Date))