>>Why not just test for the presence of the innerexception != null and if it isn't set the errormessage to that text.
>>
>>

>>   var msg = "";
>>   if(string.IsNotNull(ex.InnerException))
>>   {
>>        msg = ex.InnerException;
>>        throw new DuplicatePropertyException(msg);
>>   }
>>
>>

>
>This is not what I am asking. I am asking specifically about
>
>throw ex
>
>part.
>
>In the throw ex is there a way to append that inner exception? E.g. what should I throw?

You care a new message like I showed you and throw a new exception with that message. You can't append to ex.