Working With Routes in MVC Framework

The preceding table will help to understand valid URLs for a specified pattern.

Here is how the Routing Engine extracts segments from requested URLs.



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In the first example the URL is being mapped to the Admin Area. So we need to hard-code the folder path using the pattern Admin/{controller}/{action}.
Here we have only 2 segments, the controller and action. If we request ~/Admin/HR then it determines the view Index that is specified in the default value.

Prioritizing Controllers

When we request a URL and the routing engine recognizes it then the framework extracts the value of the controller from the segment and searches for the specific class, for example if I request URL http://localhost/ Home then it will search the HomeController class and it is not a fully qualified name, in other words if we have 2 HomeController classes in different assemblies then it will throw an exception as in the following:



We can overcome these using prioritizing controllers. We can specify a namespace as:

Routing Request for Physical Files on Disk

Apart from mapping the request directly to the controller action we can redirect the request to the physical file on disk.

We can do this using :

Note: We must specify it before registering routes.

Handle Dynamic URLs

For handling dynamic requests we use {*catchall} in the URL pattern, for example:

Now we have already seen valid and invalid URLs for our mapped routes. But {*catchall} has the ability to handle all of them. Here is how {*catchall} maps URLs to actions:

Creating a Route Constraint

Using a route constraint, we can force browser requests to use a specific route. We also define constraints if we want to specify an action for only POST, GET and so on requests called HttpMethod constraints.

Let's have a look at a route:

But what if we request a URL as in the following:

So we never want the user to pass FALSE or any string in the id segment.

For this we use a constraint and validate it for integers only using regular expressions.

HttpMethod Constraint

We use these constraints if we want to specify a route for a specific HttpMethod like GET, POST and so on.

Let's have a look at the same route. If we want to invoke this route only for POST requests then I can use :

We just need to specify another parameter for that.

It must be noted that we need to specify this route first when registering routes.

Important Points:

1. When we request a URL it always searches for the first match, not the best match, because it doesn't have any idea of the action and controller, it just extracts values from segments.
2. You need to be concerned with the order of the routing whenever you specify a new route for your application because it may cause unexpected behaviour when you do so.
3. Don't define unnecessary routes in your application.
4. Specify default values for routes (or use *catchall for unexpected behaviour ).

Summary

In this article, we have seen how routing works in MVC . We have also discovered some hidden parts of routing too. Although I have tried to cover at-most I could do and I tried to explain the most useful features. But routing has many, many more useful features. I hope you will love discovering those on your own.

Your feedback and comments are most welcome.