Why is IsDBNull throwing a conversion overflow exception? - asp.net

Question

I have a pretty simple code snippet here that is causing me a lot of problems. I also want to mention that using statements should be used, but the code was not originally authored by me. I'll likely fix this at some point
Dim dbShippableOpenOrders As New sqlCommand(sqlText, objConn)
Dim rsShippableOpenOrders As sqlDataReader = dbShippableOpenOrders.executeReader
...
If IsDBNull(rsShippableOpenOrders("cost")) Then
cost = 0
Else
cost = rsShippableOpenOrders("cost")
End If
I can't seem to figure out why this code is producing the following error message:
Conversion overflows.
Description: An unhandled exception occurred
during the execution of the current web request. Please review the
stack trace for more information about the error and where it
originated in the code.
Exception Details: System.OverflowException: Conversion overflows.
Source Error:
Line 355: End If
Line 356:
Line 357: If IsDBNull(rsShippableOpenOrders("cost")) Then
Line 358: cost = 0
Line 359: Else

Answer 1

Try the following:
Dim cost As Decimal = 0
Dim dbShippableOpenOrders As New SqlCommand(sqlText, objConn)
Dim rsShippableOpenOrders As SqlDataReader = dbShippableOpenOrders.ExecuteReader()
If rsShippableOpenOrders.HasRows Then
While rsShippableOpenOrders.Read()
If rsShippableOpenOrders("cost") IsNot Nothing AndAlso Not IsDBNull(rsShippableOpenOrders("cost")) Then
cost = CDec(rsShippableOpenOrders("cost"))
Else
cost = 0
End If
End While
End If
Here's a sample method:
Public Sub GetDataTblProduct(connectionStr As String)
Dim sqlText As String = "Select * from Product"
Dim cost As Decimal = 0
Using con As SqlConnection = New SqlConnection(connectionStr)
'open
con.Open()
Using dbShippableOpenOrders As SqlCommand = New SqlCommand(sqlText, con)
Using rsShippableOpenOrders As SqlDataReader = dbShippableOpenOrders.ExecuteReader
If rsShippableOpenOrders.HasRows Then
While rsShippableOpenOrders.Read()
If rsShippableOpenOrders("cost") IsNot Nothing AndAlso Not IsDBNull(rsShippableOpenOrders("cost")) Then
cost = CDec(rsShippableOpenOrders("cost"))
Else
cost = 0
End If
'Debug.WriteLine("cost: " & cost)
End While
End If
End Using
End Using
End Using
End Sub