SQLCommandBuilder - GetUpdateCommand, GetInsertCommand and GetDeleteCommand Questions

As I posted in my previous question I have a VB 2005 app which displays 3 fields from a SQL-Server table in a DataGridView.  2 columns are there but not visible, including the primary key.  While the below code "works" as far as committing the changes in the DataGridView control to the database when I click the Save button, I don't understand why.  I looked at the CommandText for the UpdateCommand object generated by the GetUpdateCommand method and while it was readable, I couldn't tell how it was getting the parameters populated.  I also couldn't tell how it would insert or delete records but it seemed to.

    

'Declared in a "Globals" Module:
Public gdaMyDataAdapter As New SqlDataAdapter
Public gdtMyDataTable As New DataTable

'Populate the Grid...
Public Sub PopulateGrid()

Dim sSQL As String
Dim cn As New SqlConnection(MyConnectionString)
cn.Open()

sSQL = "SELECT MyKey, col1, col2, col3, OtherKey FROM MyTable WHERE OtherKey = 1234"

Dim cmdSelect As New SqlCommand(sSQL, cn)
gdaMyDataAdapter.SelectCommand = cmdSelect

'Not sure I need to do these here or if they conflict with the ones in "save"
Dim MyCommandBuilder As New SqlCommandBuilder(gdaMyDataAdapter)
gdaMyDataAdapter.UpdateCommand = MyCommandBuilder.GetUpdateCommand(True)

gdaMyDataAdapter.Fill(gdtMyDataTable)
MyDataGridView.DataSource = gdtMyDataTable

End Sub

'Save.  Called by a button click event procedure....

Public Sub GridSave()

Dim MyCommandBuilder As New SqlCommandBuilder(gdaMyDataAdapter)

MyCommandBuilder.GetUpdateCommand()

'Below two calls seem to do NOTHING.
MyCommandBuilder.GetDeleteCommand()
MyCommandBuilder.GetInsertCommand()

'As a test, I was able to override the CommandText for the DataAdapter's UpdateCommand object like this:
gdaMyDataAdapter.UpdateCommand.CommandText = "<Various Tweaks of the Edited UPDATE query string>"

iRows = gdaMyDataAdapter.Update(gdtMyDataTable)
gdtMyDataTable.AcceptChanges()

End Sub

Select allOpen in new window

I would like to know why the GetInsertCommand and GetDeleteCommand don't set the corresponding DataAdapter command objects but the GetUpdate seems to cover it all (Insert/Delete/Update) when I make many changes via the grid with a single call  (da.Update(dt)).

Where I am going is that I am having trouble getting the Update to Insert anything other than NULL for "OtherKey".  MyKey is in the underlying table as an identity column and it is invisible in the grid.  I have the user add rows directly to the grid by typing values in col1, col2 and col3.  I have "OtherKey" stored in a TextBox on Form1.  I'd like to have "OtherKey" be invisible in the grid and get the value from a variable that was set from the TextBox.  No matter how I tweak the UPDATE all I seem to be able to send my table is a NULL.

If I'm unclear or you need any more info, please let me know.

Regards,
Eric