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POAsp.Net MVC Actions - Separation of Concerns/Single Responsibility Principle
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  1. POAsp.Net MVC Actions - Separation of Concerns/Single Responsibility Principle
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    copied!<p>In computer science we've been taught that each method should do one thing and one thing only. I'm a little confused then that we see MVC actions like the following <a href="http://www.nerddinner.com/" rel="noreferrer">given as examples of good practice</a>:</p> <pre><code> [AcceptVerbs(HttpVerbs.Post), Authorize] public ActionResult Edit(int id, FormCollection collection) { Dinner dinner = dinnerRepository.GetDinner(id); if (!dinner.IsHostedBy(User.Identity.Name)) return View("InvalidOwner"); try { UpdateModel(dinner); dinnerRepository.Save(); return RedirectToAction("Details", new { id=dinner.DinnerID }); } catch { ModelState.AddModelErrors(dinner.GetRuleViolations()); return View(new DinnerFormViewModel(dinner)); } } </code></pre> <p>Basically this piece of code provides a lot of functionality:</p> <ol> <li>Defines how to access the Action - Post only</li> <li>Defines who can access the Action - Authorize</li> <li>Accesses persistence mechanism - dinnerRepository</li> <li>Accesses state information - (User.Identity.Name)</li> <li>Converts NameValueCollection to strongly typed object - UpdateModel()</li> <li>Specifies 3 possible ActionResults and content for each - InvalidOwner/Details/Edit views</li> </ol> <p>To me this seems like too many responsibilities for one method. It is also a fairly simple action ie it doesn't deal with common scenarios like:</p> <ol> <li>Checking business rules - "Never trust user input"</li> <li>Navigation paths - On successful save always returns to "Details"</li> <li>Different return types - Someone wants to call "Edit" from a grid and needs a JsonResult?</li> <li>Better error handling - YSOD if the database is not accessible during GetDinner(id)</li> <li>Constructing additional view data - SelectLists for Drop down lists</li> </ol> <p>Not too mention the amount of testing required around this single method i.e. mocking/faking for FormCollection/UserIdentity/Authorization Provider/Repository/etc. </p> <p>My question is how do we avoid cramming so much stuff into our controller actions? </p> <p>I tend to think <a href="http://codebetter.com/blogs/jeremy.miller/archive/2008/10/23/our-opinions-on-the-asp-net-mvc-introducing-the-thunderdome-principle.aspx" rel="noreferrer">"opinions"</a> are a great concept, especially the "Thunderdome Principle". While I have great respect for the guys involved with building <a href="http://fubumvc.pbworks.com/" rel="noreferrer">FubuMVC</a> and their reasons behind doing so, I need something I can use right now. </p> <p>Edit - Well it seems I was after something like this - <a href="http://flimflan.com/blog/SampleOpinionatedController.aspx" rel="noreferrer">Opinionated Controller</a>. I'll need to examine it further as it's for MVC Preview 5 so i may need to update it myself.</p>
 

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