VB.NET generic function for checking for a value of null

Question

I am trying to write a generic function that will check each database parameter to see if it is null, and if so, return DBNull; if not, return the object.

So here is my function:

Public Shared Function CheckForNull(ByVal obj As Object) As Object
    If obj <> Nothing Then Return obj Else Return DBNull.Value
End Function

My problem is that some of the objects I am passing to the function are Nullable. So I may pass the function a Long? or Int?, but when a nullable type is passed to the function, it is converted to its value type. So if I pass a Long? that has a value of 0, the function returns DBNull because the Long? is converted to Long and a value of 0 for a Long is equivalent to Nothing. Is there anyway to make this function work for Nullable types as well?

If not, I will just fall back to using the following statements instead of one generic funciton call:

IIf(nullableVar.HasValue, nullableVar, DBNull.Value))

and

IIf(nonNullableVar IsNot Nothing , nonNullableVar, DBNull.Value))

Answer 1

That is not why your logic is failing. When evaluating an expression like (x=y) or (x<>y), if either argument is Nothing, VB.Net returns FALSE. Your conditional is always falling through to the ELSE clause. So instead of:

if obj <> Nothing then

try this instead:

if obj isnot nothing then