In Response to Sahil Malik's Null problem

January 25, 2005
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In response to your rant about the inelegance of the CLR’s null implementation:

I think you’re off track here.  ADO.NET mirrors the same type dissonance that exists between SQL Datatypes and most programming types.  While Nullable<> will help, it isn’t a panecea.  We will still need to check for null (or DbNull) values.  In your example, I would have:

  DataColumn dc = new DataColumn() ;
  dc.Name = "TotalCost" ;
  dc.type = typeof(money) ;
  dc.Expression = "price * quantity" ;

Because this value could (DbNull == true), the resulting value of (price * NULL) is NULL just like in SQL.  You could get around this by providing default values, but that just extends the problem.

This seems like an elegant solution…just check for IsNull first:

  if (dataRow[“price”] == DbNull.Value)
    // ...

Or do it in your expression:

  dc.Expression = “isnull(price, 0, price) * isnull(quantity, 0, quantity)”;

Does this make any sense?