WEB402: Design Considerations for ASP.NET MVC Applications

2. WEB402: Design Considerations for ASP.NET MVC Applications Dino Esposito R&D Manager Crionet Solutions (dino.esposito@crionet.it)

3. Content • Controllers • Structure of the class & implementation of methods • Injection of dependencies • Defining data models for the views • Action filters and AOP

4. Controller methods vs. Button1_Click • Abstractly speaking, some inherent similarities exist … public ActionResult Index(...) { // Perform the expected task // and render the next view } public void Button1_Click(...) { // Perform the expected task // and update server controls }

5. Role of the controller Button1_Click Controllers Tightly bound to user requests Further layering is up to you Full testability … if dependencies are properly managed Input data comes from parameters Response results from view engines • Tightly bound to events • Further layering is up to you • Impractical to test • … even when layered • Input data comes through server controls • Response results from server controls

6. What flavor of controller would you like?Applicable stereotypes from RDD • Service Provider • Performs work • Controller • Makes decisions and closely directs the actions of other objects • Coordinator • Reacts to events by delegating tasks to others

7. Fat-free controllersLean and mean collections of endpoints • Extremely simple action methods • Single call to get data for the view • Yield to the view engine • Grab exceptions via attributes • Who really does the job? • Controller delegates to other components the task • Arranges data into a view model

8. Fat-free controllers Dream code Handles all exceptions as may be raised • [HandleError] • public class BookingController : Controller • { • public IBookingControllerActionServiceActionService { get; private set; } • public BookingController(IBookingControllerWorkerService service) • { • Contract.Requires<ArgumentNullException>(service != null); • ActionService = service; • } • [BookingAddHandleError] • public ActionResult Add(BookingAddInputModelinputModel) • { • Contract.Requires<ArgumentNullException>(inputModel != null); • var model = ActionService.InsertNewBooking(inputModel); • return View(model); • } • : • } Handles any exceptions raised within the action Unpacks input data Calls the middle tier Creates view model Packs data into model

9. Action servicesPart of the presentation layer Controller Exception layer Action Action Action Input View model Action exception service Action exception service Action exception service Action Service Action Service Action Service Service (Application) Layer Domain Model Data Access Layer

10. Fat-free controllers demo

11. One step furtherDo we really need controllers? • Is the controller a mere pass-through layer? • Stateless and mere container of (rich & componentized) actions • Fundamental part of the ASP.NET MVC deal • Food for thought • Controller-less actions • Command pattern in a custom invoker • Instantiate an action object with methods based on HTTP verbs • Implementation: still needs to implement IController

12. View ModelsData worked on in the view • Classic weakly-typed approach • ViewData works well, easy to use, easy to understand • Strongly-typed approach • Avoid magic strings/casts, catch errors at compile time, IntelliSense • IMHO, only viable option in medium-sized applications • Dynamic approach • Based on dynamic type in .NET 4

13. Dynamic view models demo

14. Frequently required componentsController factory • Every requests passes through the controller factory • Write yours and gain control over the request lifecycle • Nice things to do • Set your tailor-made invoker • User ad hoc controllers for some types (or bypass controllers) • Plug in your favorite IoC framework • Trigger MEF composition

15. Frequently required componentsAction invoker • Controls the performance of any action for a controller • Write yours and gain control over the code being executed • Nice things to do • Set culture on the current thread • Add/remove action filters • Override methods to control/alter request lifecycle

16. Unity-based controller factory demo

17. Action filtersNative aspect-orientation of ASP.NET MVC • Pre/post process actions • Pre/post process generation of action results • Built-in filters • Authorization, error handling, output caching

18. Action filtersGallery • Detect which of many submit buttons was clicked • Complete the view model with common/shared data • Compress/Track/Customize output • Build browser-specific views for any action • Load filters dynamically (from a configuration file)

19. Multiple submit buttons demo

20. Conclusions • Fat-free controllers • Strongly-typed view • Single Responsibility Principle • Leverage built-in capabilities (binding, filters, contracts) • Build your own facilities on top of ASP.NET MVC capabilities

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