Hello Jin,
The connection string is not bound to a domain class but a domain model instead.You should have as many connection strings as models (.rlinq files) that you have in your application that access the same database. There is also an approach that allows for expanding the model metadata during runtime without changing the connection string and ultimately allowing to work with only one connection string in all modules of an application. Here is a link to a help article describing the mentioned approach.
Greetings,
Zoran
the Telerik team
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