ComboBox Linq DataSource in Hierarchy Grid Use Parent (MasterKeyField) ID in Where Clause !

[Hamid]

Hello

I Have a Grid in hierarchy mode (3 level).
In last level , in edit Form Template i have a ComboBox (LoadOnDemand) with a Linq DataSource.

I need to this dataSource , 'where expression' add a parameter.
This Parameter Value is in Grid Level 2 (att.) ... (DataKeyValue / Relation ID)

How ... ?