In order to achieve your goal you may use the Fluent Mapping API. Through this API you can map your existing classes to the relational objects such as tables in the database. Here
is a dedicated help section that elaborates on the steps needed to perform the mapping. With the visual designer approach you can either reverse map a database schema or create your entities in the diagram but the classes associated with the diagram are always automatically generated. That is why you cannot drag a user defined class to the diagram.
We do hope you will find the help section useful. Do not hesitate to contact us should any questions arise.
All the best,
the Telerik team
Registration for Q1 2011 What’s New Webinar Week is now open. Mark your calendar for the week starting March 21st and book your seat
for a walk through all the exciting stuff we ship with the new release!