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    <p>OK, let's try <a href="http://www.viddler.com/explore/mvcconf/videos/1/">putting this controller on a diet</a>.</p> <p>We start by fixing your repository and leaving it return null instead of some default post with ID = 0 which was kind of weird as you noticed:</p> <pre><code>public Post FindPost(int id, bool filterByPublished = false) { var query = db.Posts.Where(post =&gt; post.PostID == id); if (filterByPublished) query = query.Where(post =&gt; post.IsPublished == filterByPublished); return query.Select(post =&gt; post).SingleOrDefault(); } </code></pre> <p>then we could write a custom model binder for the <code>Post</code> model:</p> <pre><code>public class PostModelBinder : IModelBinder { private readonly IPostsRepository _repository; public PostModelBinder(IPostsRepository repository) { _repository = repository; } public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext) { var postIdValue = controllerContext.Controller.ValueProvider.GetValue("postid"); int postId; if (postIdValue == null || !int.TryParse(postIdValue.AttemptedValue, out postId)) { return null; } return _repository.FindPost(postId, true); } } </code></pre> <p>which could be associated with the <code>Post</code> type in <code>Application_Start</code>:</p> <pre><code>var postsRepository = DependencyResolver.Current.GetService&lt;IPostsRepository&gt;(); ModelBinders.Binders.Add(typeof(Post), new PostModelBinder(postsRepository)); </code></pre> <p>and then a custom action filter that will take care to short-circuit the action in case the post is null or the post slug is different than the one passed as parameter:</p> <pre><code>public class PostActionFilterAttribute : ActionFilterAttribute { public override void OnActionExecuting(ActionExecutingContext filterContext) { var postParameter = filterContext .ActionDescriptor .GetParameters() .Where(p =&gt; p.ParameterType == typeof(Post)) .FirstOrDefault(); if (postParameter == null) { return; } var post = (Post)filterContext.ActionParameters[postParameter.ParameterName]; if (post == null) { filterContext.Result = new RedirectResult(Url.Home()); } var slug = filterContext.Controller.ValueProvider.GetValue("slug"); if (slug != null &amp;&amp; post.Slug != slug.AttemptedValue) { filterContext.Result = new RedirectResult( Url.ShowPost(post.PostID, post.Slug), true ); } } } </code></pre> <p>If you are using ASP.NET MVC 3 this custom attribute could be registered as a global one in <code>Global.asax</code>:</p> <pre><code>public static void RegisterGlobalFilters(GlobalFilterCollection filters) { filters.Add(new PostActionFilterAttribute()); ... } </code></pre> <p>and finally your controller action will become:</p> <pre><code>public ActionResult ShowPost(Post post) { postRepository.PostVisited(post); var viewModel = Mapper.Map&lt;Post, PostViewModel&gt;(post); return View(viewModel); } </code></pre> <p>or even bringing this a step further and introducing a custom mapper action filter:</p> <pre><code>[AutoMap(typeof(Post), typeof(PsotViewModel))] public ActionResult ShowPost(Post post) { postRepository.PostVisited(post); return View(post); } </code></pre> <p>The <code>AutoMap</code> action filter is pretty easy to implement. You would subscribe to the <code>OnActionExecuted</code> method and check whether the returned result from the controller action was a <code>ViewResultBase</code> and then extract the model from it, pass it to AutoMapper given the 2 types and substitute the model with the view model.</p>
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    1. USDarin Dimitrov
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    1. COHoly moley! That is seriously one hell of an answer. I didn't expect anything anywhere near as fleshed out as this. This has given me so much to work with and so many new ideas too. Thank you so much.
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    2. COjohn H - that made me laugh. but very true. darin, on the ball (and running) as ever
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    3. CO@jim Darin's helped me several times already on SO, and judging by his rep, countless others too. So credit where it's due and hopefully, like you, a smile along the way. :)
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