[DotNetDevelopment] Testing for DBNull, causes Invalid Cast Exception

[JaffaB]

Hi All,

i am trying to use a variable from a DST in a VS2003 project, and I am
trying to overcome an Invalid Cast Exception of DBnull.  But
everything I try to test for DBnull, causes the exception as well.

At first, I used a function to check and convert as follows:

                public static string MNS(object s)
                {
                        if(s==System.DBNull.Value)
                                return string.Empty;
                        else
                                return Convert.ToString(s);
                }

However, calling this (passing in the column of the table as shown
below) caused the same casting exception.  Now I have gone specific
with the test as follows:

DstWastage.AuditRow drAudit = dstWastage.Audit[0];
if(drAudit.ContainerCode.Equals(System.DBNull.Value) == true) sqlains
= SqlCEParamAdd(sqlains,""); else sqlains = SqlCEParamAdd
(sqlains,drAudit.ContainerCode);

the 2nd line, produces the exception error of Invalid Cast Exception :
StrongTyping_CannotAccessDBNull.

I have also tried..

DstWastage.AuditRow drAudit = dstWastage.Audit[0];
   if(drAudit.ContainerCode == System.DBNull.Value) sqlains =
SqlCEParamAdd(sqlains,""); else sqlains = SqlCEParamAdd
(sqlains,drAudit.ContainerCode);

However, this wont even compile, as it says it cannot compare the
string (drAudit.ContainerCode) with a type of System.DBNull.Value

Can anybody point me in the right direction for sorting out whether
the variable is a DBnull or not.