How to Compare nullable objects - asp.net

Question

I need to compare a current List of Objects from a DB against a new List of Objects. I want to compare them and highlight for the user those which have changed (in this case, return TRUE that they are different).
Since some of my objects are Nullable, this involves a lot of IF NOT IS Nothing on the side of the NewObj and the CurrentObj...I've trying to find a more efficient way of writing the below as I have to use it to compare about 30 objects of different types, IE Date, Decimal, Int, etc..
The below works until say either of the Obj has no Rank and is therefore Nothing
Suggestions?
Dim Rank As Boolean = CompareData(NewObj, CurrentObj, "Rank")
Dim Regiment As Boolean = CompareData(NewObj, CurrentObj, "Rank")
Dim DateofBirth As Boolean = CompareData(NewObj, CurrentObj, "DoB")
Private Function CompareData(NewObj As Business.Casualty, CurrentObj As Business.Casualty, FieldToComapre As String) As Boolean
Select Case FieldToComapre
Case "DateOfBirth"
Return (Nullable.Equals(NewCasualty.DateOfBirth, CurrentCasualty.DateOfBirth))
Case "Age"
Return (Nullable.Equals(NewCasualty.Age, CurrentCasualty.Age))
Case "Rank"
Return (Nullable.Equals(NewCasualty.Rank.ID, CurrentCasualty.Rank.ID))
Case "Regiment"
Return (Nullable.Equals(NewCasualty.Regiment.ID, CurrentCasualty.Regiment.ID))
Case Else
Return True
End Select
End Function

Answer 1

My first suggestion is to change the name of your function to something like AreFieldValuesTheSame. My second suggestion is to negate the purpose of the function. In other words, return True when the values are the same.
If you follow my first two suggestions, then for each one of your cases, instead of simply
Return (Nullable.Equals(a.ID, b.ID))
you need something more like
Return ((a Is Nothing And b Is Nothing) Or (a.ID Is Nothing And b.ID Is Nothing) Or (Nullable.Equals(a.ID, b.ID)))
For example, a represents NewCasualty.Rank and b represents CurrentCasualty.Rank. You need to check for the object being Nothing (null in other words) before you try to check properties of the object.
Also, at the beginning of the function, you need to check whether NewObj Is Nothing and whether CurrentObj Is Nothing:
If (NewObj Is Nothing) And (CurrentObj Is Nothing) Then
Return True
Else If (NewObj Is Nothing) Or (CurrentObj Is Nothing)
Return False
Please forgive me if my VB syntax is not perfect. (I'm much more fluent in C#.)

Answer 2

I actually ended up just going with an Extension method..it was simpler and cleaner IMO.
Dim Rank As Boolean = CompareData(NewObj, CurrentObj, "Rank")
Dim Regiment As Boolean = CompareData(NewObj, CurrentObj, "Regiment")
Dim Trade As Boolean = CompareData(NewObj, CurrentObj, "Trade")
Private Function CompareData(NewObj As Business.Casualty, CurrentObj As Business.Casualty, FieldToComapre As String) As Boolean
Select Case FieldToComapre
Case "Trade"
Return NewCasualty.Trade.NullableEquals(CurrentCasualty.Trade)
Case "Rank"
Return NewCasualty.Rank.NullableEquals(CurrentCasualty.Rank)
Case "Regiment"
Return NewCasualty.Regiment.NullableEquals(CurrentCasualty.Regiment)
Case Else
Return True
End Select
End Function
public static class NullableCompare
{
public static bool NullableEquals<T>(this T s1, T s2)
where T : class
{
if (s1 == null)
{
return s2 == null;
}
return s1.Equals(s2);
}
}
public partial class Rank
{
public override bool Equals(object obj)
{
var p2 = obj as Rank;
if (p2 == null)
{
return false;
}
if (this.ID != p2.ID)
{
return false;
}
return this.ID == p2.ID;
}
public override int GetHashCode()
{
return this.ID.GetHashCode();
}
}