ASP.NET MVC

Patterns and Anti-Patterns:Lessons from the Trenches

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Anti-Patterns: Things NOT to do• Return un-typed ViewData on a GET• Pass low-level data-types on POST• Pass FormCollection on POST• Magic Strings in Views• Logic in Views• ‘Fat’ Controllers• Domain Models passed to and from Views• Exposed Primary Keys in URLs• (unverifiable) Convention over Configuration

Return Untyped ViewData on a GETpublic ActionResult Register(){

ViewData["PasswordLength"] = MembershipService.MinPasswordLength;return View();

}<p> Passwords are required to be a minimum of <

%=Html.Encode(ViewData["PasswordLength"])%> characters in length.

</p>

Pass Low-Level data-types on POSTpublic ActionResult LogOn(string username,

string password)

{if (!ValidateLogOn(username, password)){

return View();}

}

Pass FormCollection on POSTpublic ActionResult LogOn(FormCollection collection){

if (!ValidateLogOn(collection["userName"], collection["password"]))

{return View();

}}

Magic Strings in Views<p>Please enter your username and password.<%= Html.ActionLink("Register", "Register")%> if you don't have an account.</p>

Logic in Views<%if (((DateTime)ViewData["OrderDate"]) > new

DateTime(2009, 9, 1)){

foreach (Product product in (IList<Product>)ViewData["Products"])

{%><li><%=product.ProductName%></li>

<%}}%>

‘Fat’ Controllers[AcceptVerbs(HttpVerbs.Post)]public ActionResult Edit(int id, FormCollection collection){

try{

var customer = customerRepository.Get(id);customer.Firstname = collection[("Firstname"];using(var tx = context.BeginTransaction()){

customerRepository.Save(customer);tx.Commit();

}return RedirectToAction("Index");

}catch{

return View();}

}

Domain Models passed betw Viewspublic ActionResult List(int id){

var customer = customerRepository.Get(id);return View("Index", customer);

}

[AcceptVerbs(HttpVerbs.Post)]public ActionResult Edit(Customer customer){

customerRepository.Save(customer);return View("Index", customer);

}

Exposed Primary Keys in URLshttp://host/{Controller}/{Action}/{id}

http://localhost/Customer/Edit/34http://localhost/Product/View/34

http://localhost/Customer/Edit/Bohlenhttp://localhost/Product/View/WSTV123

(unverifiable) Convention over Configuration

public ActionResult Register(){ViewData["PasswordLength"] = MembershipService.MinPasswordLength;return View();

}

Patterns: Things to DO• Strongly-Typed Model In and Model Out– ViewModels, UpdateModels

• Encapsulate View ‘decisions’ in ViewModels• Controller controls the View, NOT the app

Strongly-Typed Model In and Outpublic ActionResult List(int number){

var customer = customerRepository.GetByNumber(number);var customerViewModel = new CustomerViewModel(customer);return View(“List", customerViewModel);

}[AcceptVerbs(HttpVerbs.Post)]public ActionResult Edit(CustomerUpdateModel updCustomer){

var customer=customerRepository.GetByNumber(updCustomer.Number);

updCustomer.ApplyChangesTo(customer);customerRepository.Save(customer);var customerViewModel = new CustomerViewModel(customer);return View("Index", customerViewModel);

}

Encapsulate ‘decisions’ in ViewModels<%if (CustomerViewModel.HasRecentOrders)

{foreach (Product product in

(CustomerViewModel.Products){%>

<li><%=product.ProductName%></li><%}

}%>

Controller controls the View, not the app[AcceptVerbs(HttpVerbs.Post)]public ActionResult Edit(CustomerUpdateModel updCustomer){

var customerViewModel=customerUpdateService(updCustomer)return View("Index", customerViewModel);

}

Suggestions to Extend MVC• MVCContrib (mvccontrib.org)• xVal (xVal.CodePlex.com)• 1000s of JQuery Plugins

Discussion• Other Experiences• Other Challenges• Other Recommendations

Session Wrap-Up• Thoughts and Impressions– Positives and Deltas

• Discussion of Topics for Upcoming Meetings