While you can define service layer operations any which way you want to fit your application architecture, the default implementation leverages stateful communication with the service layer to allow a better reuse of the service operations.

In particular, the Create service method is supposed to just create a new object in memory on the business layer and return its temporary key back to the client. The client will then be able to use this temperate key to immediately call an Update service method within the same session, and then the SaveChanges in the same session to commit all the changes to the database. This way you don't have to repeat all the same input parameters for the Create method as you have for Update method.

The generated Details form works indeed only as an update form out of the box. However, this form is intended to be edited manually for the final product and can be easily updated to support creation of objects as well. What you need to do is to invoke it in a "create mode" without an object key and then call the Create service method before calling the Update during the Save button click.

We will take a look if we can update the generators to generate such forms in both create and update modes.