gistfile1.cs

    public class HostedByCheckAttribute : ActionFilterAttribute {
        public override void OnActionExecuting(ActionExecutingContext filterContext) {

            var postId = filterContext.ActionParameters["id"] as int;
            var postsRepo = new PostsRepository();
            var post = postsRepo.Get(postId);

            if (!post.IsHostedBy(/* ... */)) {
                filterContext.Result = new ViewResult { ViewName = "InvalidOwner", ViewBag = filterContext.Controller.ViewBag, ViewData = filterContext.Controller.ViewData };
            }
        }
    }

    public class HostedByCheckAttribute : ActionFilterAttribute {
        [Inject]
        public IPostRepository Repo { get; set; }

        public override void OnActionExecuting(ActionExecutingContext filterContext) {

            var postId = filterContext.ActionParameters["id"] as int;
            var post = Repo.Get(postId);

            if (!post.IsHostedBy(/* ... */)) {
                filterContext.Result = new ViewResult { ViewName = "InvalidOwner", ViewBag = filterContext.Controller.ViewBag, ViewData = filterContext.Controller.ViewData };
            }
        }
    }