MVC changes in Zend Framework

Several months ago, Andi asked me to take the role of lead developer on a refactoring of the Zend Framework MVC components. I agreed, though somewhat reluctantly; I already maintain another MVC library, and wasn't sure how well I could fill the shoes of people like my friends Mike, who had done the initial development on the controller classes, and Paul, who provided Zend_View.

The experience has been incredibly rewarding, however, and I've had the chance to pick the brains of and work with some top-notch developers in the process. In the next week or so, we'll be releasing version 0.6.0 of the framework, and it will include much of my work in the MVC components as part of the core distribution. A big thanks to all those who have contributed opinions, design help, code, tests, and documentation; another thank you goes to Andi for trusting and supporting me in this endeavor.

So, what are the changes? Read on to find out...

Most of the changes lie under the hood at this point; the most basic usage of the MVC components remains the same. The changes introduced mainly promote greater flexibility and testing. In fact, the most significant changes, the introduction of request and response objects, are transparent to most users, but are the very changes that make unit testing of the MVC components both possible and easy.

So, as you may have guessed, the controller classes are now unit tested; coverage isn't perfect, but it's reasonable (currently around 68% code coverage), and an improvement over the basically zero coverage from before (only Martel's RewriteRouter had tests before I started). What this means to developers is that from this point forward, any changes to the controller classes will need to pass regression tests... and those tests actually exist. It also means that it is now possible to unit test applications without needing a web server; this is going to be a big step for MVC applications based on the framework.

By introducing the request and response objects, we now no longer need to rely on a web environment in order to make requests; having a response object makes it trivial to capture output from the various action controllers and then test against expected results. This is a huge change.

Additionally, by de-coupling the controllers from the request environment, it becomes possible to use the MVC components in non-web environments. Think CLI and PHP-GTK.

Another change is that a router is no longer needed. This allows developers to use the MVC components in non-web environments, where routing may not actually be necessary, as well as to use the MVC components in web environments where pretty URLs are difficult to configure. IIS, for instance, doesn't have a mod_rewrite equivalent out-of-the-box, so being able to specify a url such as http://localhost/index.php?controller=index&action=view and have it dispatch properly is a nice feature.

A feature that many were requesting was the ability to push parameters into the front controller, and have those push through to each of the router, dispatcher, and action controllers. Such an ability would obviate the need for a registry, and also allow the entire controller chain to share an environment. I made use of this today when a request came in for the ability to specify an optional module parameter in the request URI; instead of breaking backwards compatability or creating new routers and dispatchers, I was able instead to simply push a 'useModules' setting through the chain, and if discovered, act on it. (This new feature allows urls such as http://localhost/module/controller/action to dispatch to Module_Controller::actionAction(); think controller classes in subdirectories.)

One feature that I think a lot of people don't understand is the Response object. It is a container for the entire response generated by a request, whether that's from a single or multiple actions. As such, it also aggregates exceptions from the process. It's final purpose is to return that response to the client, and this is done by simply echo()ing it; its __toString() method should take care of any final rendering to perform.

The basic response object provided with the new system does very little. It allows for the setting and aggregation of content through its setBody() and appendBody() methods, as well as setting headers via setHeader(). If exceptions occur, they are registered via setException(). The suggestion made in the documentation is to use appendBody() to aggregate content, and then have __toString() return the aggregated content en masse by echoing the response at the end of the dispatch loop: echo $front->dispatch().

While this is nice, there are some much more interesting things you can do with it. In a recent project I did, I integrated Zend_View and Zend_Json in the response object, and added accessors in my action controllers to push content to the response object. Then, based on the request, I could switch between returning JSON strings or XHTML content. If an exception occurred, I could redirect to an error page, or, in the case of an AJAX request, return an error encapsulated in a JSON string. This type of context switching is very powerful, and I'll blog more about how it can be achieved later.

If you already use the framework MVC but haven't tried the new code, I encourage you to download a snapshot or grab it from subversion and give it a spin; there's a document covering migration, and any feedback or additions on this would be greatly appreciated (this document in the framework wiki is currently out-of-date; check the docbook in the framework distribution you download for more current information).

If you haven't tried the framework MVC, and are interested in MVC libraries, give it a whirl and let me know what you think!

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