Hi Ant Lu,
I have tested the case you have provided and I can confirm that everything works out fine.
In order to see the available data sources that come from your ria data service you need to have opened a silverlight page. Please note that there is a slight delay from the time you open the data source tab to the time when it is actually populated. This occurs because of the code generation that needs to be done in order for you to have the actual data sources.
Please also note that you need to rebuild your web project after you have added the domain service.
I hope that helps.
the Telerik team
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