I tried to use Business Object Mapper to map the table to a business object. I found that I only can select one table. Is it possible that business object can work with more than one tables? For example, a business object can select the fields from three tables.

As long as the view is an indexed view on SQL Server, allowing you to INSERT, UPDATE, and DELETE records from it, then what you have done is fine.  You might even be able to define a primary key index on the view within SQL Server, allowing you to avoid having to change that code each some you rebuild the partial class within SQL Server.