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How to handle null values

ADO.NET provides database connectivity between relational and non relational systems through a common set of components. The ADO.NET classes are divided into two components, the Data Providers and the DataSet.

In many situations while reading data from Dataset, we have seen the error message like this,

  Conversion from type 'DBNull' to type '' is not valid

Here is the solution for how to handle DBNull. The DBNull class represents a nonexistent value. The function IsDBNull returns True if the data type of expression evaluates to the DBNull type otherwise, IsDBNull returns False.

  If IsDBNull(ds.Tables(0).Rows(i).Item(0)) Then
	  MsgBox("DBNULL exist in the field ")
  Else
	  MsgBox(CInt(ds.Tables(0).Rows(i).Item(0)))
  End If

In the above code we are using the function IsDBNull to check wether the Dataset value is a DBNULL or not.




Imports System.Data.SqlClient
Public Class Form1
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim connetionString As String
        Dim connection As SqlConnection
        Dim command As SqlCommand
        Dim adapter As New SqlDataAdapter
        Dim ds As New DataSet
        Dim i As Integer
        Dim sql As String

        connetionString = "Data Source=ServerName;Initial Catalog=DatabaseName;User ID=UserName;Password=Password"
        sql = "your sql select statements here"

        connection = New SqlConnection(connetionString)

        connection.Open()
        command = New SqlCommand(sql, connection)
        adapter.SelectCommand = command
        adapter.Fill(ds)
        connection.Close()
        Try
            If IsDBNull(ds.Tables(0).Rows(i).Item(0)) Then
                MsgBox("DBNULL exist in the field ")
            Else
                MsgBox(CInt(ds.Tables(0).Rows(i).Item(0)))
            End If
        Catch ex As Exception
            MsgBox(ex.ToString())
        End Try
    End Sub
End Class






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