[drupal-devel] Does the Forms API give Drupal a model view controller architecture

[Robert Douglass]

This'll be a fun discussion :-)

I see MVC in many aspects of Drupal, though none are pure 
implementations according to the Go4 and Smalltalk/Java purists.

Our controller is a combination of the menu system and the hook system. 
The menu system is responsible for all Drupal paths, and the paths are 
what determines which functions get called (via the hook system).

Our model is mapped pretty much directly to the relational database 
structure. Our main object types are Node, User, Comment with other 
types playing supporting roles.

The view is the theme system, of course.

What is interesting about MVC discussions in the context of webapps and 
Drupal is that it is really a bit out of place. The pattern is really 
the most at home in GUI design for graphical applications where widgets 
on the screen know how to render themselves based on well defined state 
information that is given to them by the controller (guess these could 
be our theme funtions). The widgets communicate a user's actions to the 
controller, which can cause state changes in the model, and the 
controller communicates model state changes to the widgets. If you look 
at it, it is very difficult to write a pure MVC pattern for a web 
application, and it is almost as difficult to *not* write some sort of 
MVC pattern for the same.

Since becoming involved with Drupal I've commented several times that 
I'm glad we *don't* dwell on MVC. It was such a fad in the late '90s. 
It's not that I'm against patterns; on the contrary, they are essential 
to understanding software and any time I learn a new pattern I become a 
better programmer. I just think that calling something MVC doesn't make 
it inherently better (bike != mercedes, no matter what Bèr will tell you 
;-))

-Robert

Kieran Lal wrote:
> Here's a quick overview of Model View Controller architectures that  was 
> updated in April 2005.
> http://www.jdl.co.uk/briefings/MVC.pdf
> 
> I haven't spent a lot of time thinking about this.
> 1) Modules represent the model.  They are unaware of the view, theme.
> 2) View - To me there are three stock views, or outputs, in Drupal.   
> The first is just themeless output.  The second is the themed  output.  
> The third is as an XML-RPC request.
> 3) Controller-this is traditionally about controlling input.  The  
> controller knows about it's views.
> 
> The question is, does Drupal have a controller, and if it does, is it  
> the Forms API.  This is a question that is consistently coming up in  
> comparing Drupal to Ruby On Rails and I'd like to have a solid answer.
> 
> Cheers,
> Kieran
>