Checking for DBNull

Posted by Jim Lahman on Geeks with Blogs See other posts from Geeks with Blogs or by Jim Lahman
Published on Fri, 04 Mar 2011 17:46:23 GMT Indexed on 2011/03/04 23:25 UTC
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Using a table adapter to a SQL Server database table that returns a NULL record. We determine the fields are NULL by comparing against System.DBNull

Looking the NULL records in SQL Management studio

Using a table adapter to retrieve a record

   1:  try

   2:  {

   3:      this.vTrackingTableAdapter.FillByTrkZone(this.dsL1Write.vTracking, iTrkZone);

   4:  }

   5:  catch (Exception ex)

   6:  {

   7:       sLogMessage =  String

   8:               .Format("Error getting coil number from tracking table at {0} - {1}",

   9:                              sTrkName,

  10:                              ex.Message);

  11:       throw new CannotReadTrackingTableException(sLogMessage);

  12:  }

Looking at the record as it returned from the table adapter:

Since each item in the ItemArray is an object, we can test for null

   1:  if (dsL1Write.vTracking.Rows[0].ItemArray[0] == System.DBNull.Value)

   2:  {

   3:        throw new NoCoilAtPORException("NULL coil found at tracking zone " + sTrkName);

   4:  }

If no records were returned by the table adapter

   1:  if (dsL1Write.vTracking.Rows.Count == 0)

   2:  {

   3:      throw new NoCoilAtPORException("No coils found at tracking zone " + sTrkName);

   4:  }

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