Cast from type 'DBNull' to type 'String' is not valid. Error


Can anyone help me with an error I am receiving "Cast from type 'DBNull' to type 'String' is not valid."  I am creating an aspx page in VB.NET, please find attached code causing error.

objCmd = New SqlCommand("USP_DisplayEmbarkDetails", objConn)
  objCmd.CommandType = CommandType.StoredProcedure
  objCmd.Parameters.Add("@BranchID", lblGetBranchID.Text)
  objRdr = objCmd.ExecuteReader()

   While objRdr.Read

  End While

The value Ext21DDI is null, therefore the lblExt21DDI should display nothing.  I have never had this problem before and I have many labels that return null values.

Any help would be greatly appreciated.



10/17/2005 1:59:21 PM 91979 articles. 4 followers. Follow

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you need to check for DBNull with IsDbNull function or Convert.IsDBNull method. And if there is DBNull value, you cannot just assign it to  variable, you need give different/default value when the given field has DBNull.

For example create following type of helper class (you can extend it with more helper methods for Integer, Decimal etc).

Public Class NZ

   Public Shared Function GetString(obj As Object, defaultstr As String) As String

      If IsDbNull(obj) Then Return defaultstr
      Return CStr(obj)
   End Function

End Class

Then, the code using it (on your loop) could be:


E.g it checks if you pass it DBNull, and returns the default, otherwise it tries to convert the given object to string with CStr function.


Teemu Keiski
Finland, EU
10/17/2005 3:46:28 PM

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