If you wish to keep a hidden data in the WebGrid you could use the HiddenDataMember on the column level, the HiddenDataMember will work if the datasource contains the column with the value you wish to hide. Here is the snippet if you wish to hold the Title value in the FirstName column:

<ISWebGrid:WebGridColumn Caption="FirstName" DataMember="FirstName" Name="FirstName"
    Width="100px" HiddenDataMember="Title">
</ISWebGrid:WebGridColumn>

The HiddenDataMember will be assigned automatically during the add row process.

In order to access the value in the client side, here is the snippet:

WebGridRowObject.GetCell('FirstName').CellElement.getAttribute('id')

It seems I misunderstand the issue, my superior send me your email:

I have a grid that has two child tables(3levels). I also have a column in each table called “VisibleLevel,” whichis hidden.

I need to populate this column automatically with the level of the band (0,1,2) when a new row is created. How do I do this on the server-side?

Attached is a simple sample if you wish to add certain data to a undisplayed data source column. During AddRow server side event you will need to set the undisplayed data source column with the value you wish. The sample will require Northwind.mdb data

In your scenario, you will need to differentiate between row added in the parent or child table, using the e.Row.Table.Name(determine the table name) / e.Row.Table.TableLevel(determine the level of the table) property in the AddRow server side event should be sufficient.