Improving Asp.net MVC maintainability and RESTful conformance

I've used Asp.net MVC for a few years now but this issue I've stumbled upon just a few days ago seems something everydayish and I wonder how come I've never bumped into it. It has to do with Asp.net MVC routing and action method selection. First of all think of default route definition that looks like this:

   1:  // default application route

   2:  routes.MapRoute(

   3:      "Default",

   4:      "{controller}/{action}/{id}",

   5:      new { controller = "Home", action = "Index", id = UrlParameter.Optional }

   6:  );

Mind that id route value is optional? Yes optional. So it should be perfectly feasible to have two action methods: one with the id parameter and one without it: public ActionResult Index() { ... } and public ActionResult Index(int id) { ... } But you've probably guessed it? This doesn't work out of the box. You'll get a runtime error stating that there are two matching action methods for the current request. A bit strange? I thought so as well. So let's try and accomplish just that!

jQuery animated "scroll into view" plugin (with additional ":scrollable" selector filter)

Sometimes our pages have to deal with long(er) unpaged lists of data. Long enough to fall off the viewable browser window estate. Actually you don't even have to deal with lists at all. Let me re-define the problem: when you have a scrollable element on your page (may be the very body of it) and you need to programmatically scroll to its out-scrolled child element, then this jQuery plugin is just for you. Now let's see when we have to do this and what could go wrong.

How to correctly use IHttpModule to handle Application_OnStart event

In one of my previous blog posts (Writing a custom IHttpModule that handles Application_OnStart event) I've been talking about using IHttpModule to also handle application start event which is a non-documented feature. Sure it works, but you may see some strange behaviour of duplicated (or even multiplicated) functionality being executed. You probably won't see this with your applications in development, because your local IIS isn't really heavy duty workhorse, but in production environment you may see this strange behaviour. Investigating it is even a bit more complicated because of the running application serving live traffic. Let me help you. So I will point you in the right direction and more importantly show you a solution that makes things work reliably even on a heavy load IIS.

Custom Asp.net MVC route class with catch-all segment anywhere in the URL

Asp.net MVC routing does a fine job with routes that have a finite number of segments. We define them with route URL pattern string. The default provided by the Asp.net MVC project template being {controller}/{action}/{id}. Most web applications can do everything using only this single route definition and many developers don't even think beyond this standard. But sometimes this single route just isn't enough or it's just not acceptable.

A real world example

Think of a web site you're building that has hierarchically organised categories. Like Amazon. We have books, music, electronics, etc. And every top category has sub categories. And so on and so forth. Using default route definition we would access a particular (sub)category simply by: www.domain.com/categories/index/647 That's fine, but it's definitely not human friendly. If we'd change our route URL definition to {controller}/{action}/{id}/{name} this would already be much friendlier: www.domain.com/categories/index/647/web-development That's something similar (not the same, because we're still using action names here) to what Stackoverflow does with it's questions.

But now think of this super human readable web address: www.domain.com/books/computer-internet/web-development/latest This one would display latest web development books. As we can see it defines categories in hierarchical order similar to breadcrumbs. All in human readable format. Doing this kind of routing isn't supported out of the box (because we have an action at the end), but I think we could do better. Let's try and create a route that supports this.

Generate enum from a database lookup table using T4

This is something rather common. You're building an application that uses database storage in the background. If your database isn't completely trivial and you're not fatally in love with magic values/numbers, then you probably also use lookup tables to gain referential integrity when it comes to certain types, codes and similar data. But to follow the DRY software development principle we want to use these values defined in database on upper layers as well without manually writing any additional code. Because as mentioned magic values are evil regardless of where they're used.

jQuery parseJSON automatic date conversion for Asp.net and ISO date strings

This one's quite common. You asynchronously communicate (a.k.a. Ajax) with your server and get JSON data in return. You most probably use $.parseJSON() on the client side which actually parses JSON string and returns an object. We've all used that. But (yes, there's always a but) there's a catch. There's no defined standard for date serialization, so jQuery will not parse your dates back to dates. What the heck even native JSON parser (these days supported in all major browsers) won't do that. So you have to do it yourself. Manually. Or, modify default jQuery functionality a bit and get it done automatically.

Custom action method selector attributes in Asp.net MVC

Some of the least customized but very useful extension points in Asp.net MVC are action method selector attributes. We use them all the time without actually knowing, but we may write our own as well and make seemingly complex things trivial.

A real world example

Take for instance Twitter website. When you first visit their site, you are presented with the anonymous visitor home page that provides search capabilities, trends etc.

But when you're logged in you see a completely different page. Web address is still the same, but content is completely different. You see your home twitter page where you can send tweets and read your stream.

Using custom action method selector attributes, you can easily differentiate between such requests without using multifaceted controller actions.

Sending complex JSON objects to Asp.net MVC using jQuery Ajax

jQuery has great support for sending HTML form data (that is input, select and textarea element values) back to the server using Ajax technologies by providing two main ways of preparing form data for submission - namely serialize() and serializeArray() functions. But sometimes we just don't have a form to send but rather JSON objects that we'd like to transfer over to the server.

Asp.net MVC on the other hand has built-in capabilities of transforming sent data to strong type objects while also validating their state. But data we're sending has to be prepared in the right way so default data binder can it and populate controller action parameters objects' properties. We can of course parse values ourselves but then we also loose the simplest yet efficient built-in validation using data annotations which is something we definitely want to use.

I know I've been sending JSON objects back to the server before, but this time I came across a problem that felt odd, since based on my previous experience should work out of the box. To my surprise it didn't. Let me explain what was going on.

Handling validation errors on Ajax calls in Asp.net MVC

If you're developing rich web clients using Asp.net MVC on the back-end, you've probably come across this functionality that can be described with these conditions:

1. client side data (may be a form),
2. ajax posting of this data (form),
3. controller action has strong type parameters,
4. controller action processes data and returns anything but a full view (since it was an Ajax call)

Familiar? Then you've come across this problem: »What should be done when validation fails?«
Seems fairly straight forward, right? Well not so fast my fellow developer friend...

Running batch files (*.bat) inside Visual Studio

This is something very simple, but very useful. Something Microsoft should've put in Visual Studio in the first place long ago. When I develop data-aware applications I usually end up writing database scripts to make it easy to (re)deploy and version control my database model. I usually write several files just to make things controllable and manageable. But deploying them is a different task altogether. And a tedious one as well. I have to fire up SQL Management Studio and then run all those scripts in correct order. Since this is done rather frequently during application development it seems like a very good candidate for automation or simplification. So let's do just that.