can't write to database

[ntgr]

hello,

 

i am new to VB.net and I am trying to make a simple program to write to a table (test1) with two fields (ID primary key and name nchar(50))

 

Also I am using dataset and dataadapter

 

I also have a form that binds the 2 fields.

 

I have this button that binds the fields successufully

 

    Private Sub btn_bind_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_bind.Click

       Dim cmdupdate As New SqlClient.SqlCommand()
       Dim cmdselect As New SqlClient.SqlCommand()
       Dim prm As SqlClient.SqlParameter


       cnn.ConnectionString = "server=(local)\MSSMLBIZ;" & _
            "initial catalog=test;" & _
            "integrated security=SSPI;UID=kostas;Password=qwedsa"

       Try
           cnn.Open()
           cmdselect = cnn.CreateCommand
           cmdselect.CommandText = "select * from test1"
           testda.SelectCommand = cmdselect

           testda.Fill(testds, "customers")



           Me.BindingContext(testds.Tables("customers")).Position = 0

           txt_id.DataBindings.Add("Text", testds.Tables("customers"), "ID")
           txt_name.DataBindings.Add("Text", testds.Tables("customers"), "name")

       Catch ex As Exception
           MsgBox("error: " & ex.Source & " : " & ex.Message, _
           MsgBoxStyle.OkOnly, "btn_bind")
       End Try

   End Sub

 

 

Then I have a button that saves changes and it doesn't work

 

    Private Sub btn_save_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_save.Click
       Dim cmdupdate As New SqlClient.SqlCommand()

       Dim prm As SqlClient.SqlParameter



       Try
           cmdupdate = cnn.CreateCommand
           cmdupdate.CommandText = "update test1 set name = @name WHERE ID=@ID"


           prm = cmdupdate.Parameters.Add("@name", SqlDbType.NChar, 50, txt_name.Text)
           prm = cmdupdate.Parameters.Add("@ID", SqlDbType.UniqueIdentifier, 4, txt_id.Text)
           testda.UpdateCommand.ExecuteNonQuery()

           cnn.Close()
       Catch ex As Exception
           MsgBox(ex.ToString)
       End Try

   End Sub

I am getting this error when pressing the second button:A first chance exception of type 'System.NullReferenceException' occurred in book_demo.exe

 

can you please advice

 

thanks

[PlausiblyDamp]

Which line is the one throwing the exception? If you step through the code what is the value of testda on the line

testda.UpdateCommand.ExecuteNonQuery()

if it is non-null then what about the value of testda.UpdateCommand?

[ntgr]

it seems it is null (nothing)

[ntgr]

it seems I am missing some kind a connection of the dataset with the datatable.

 

can you please help on this one ?

[PlausiblyDamp]

The DataAdapter needs to be told what command to use when inserting, updating and deleting - you would need to assign your cmdupdate to the adapter's UpdateCommand property/