I have an existing application with a datalayer (primary EF4), a businesslayer (custom code) and a windows application - now I want to create a webapplication using ASP.NET MVC but I am not sure exactly what to do especially in my models.
When my data and business logic already exist how should I structure my Models and Controllers compared to a referenceproject like MVC Music Store v2.0 (http://mvcmusicstore.codeplex.com/)? All my entities are stored in my datalayer and all my methods and logic are stored in my businesslayer so I guess I need no Models (unless I need specific web Models) and I guess my controllers will only need to call the methods in my businesslayer as I would to in a normal webform application?
Another question, if I need to display 2 lists with data from 2 different entities on 1 page I guess I need to create af Model with 2 properties (one for each entity)?
The last one for now, if, for some reason, e.g. a Get method from my businesslayer returns an exception how should this be handled in my Controller/View?
It depends on the complexity of your application. I would at the very least introduce ViewModels for each view so you can supply the view with the data that is required. If your application is light weight it might be fine to use your business layer in the controller. However, you might want to introduce a service layer that interacts with your business layer just to keep the controllers thin.
As for exception handling, you might want to look into the HandleError attribute.