Hello Alexander Sun,
Currently when you use a ria data source and you do some modification to it the attach is done internally and you don't need to write any additional logic. As for now doing attach outside of a data source is not supported out of the box and you will have to implement some additional logic in order to do so.
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items