Re^3: Implementing Model-View-Controller

[pileofrogs]

Okay, then if I get this right, I might create an object, called User or Method::User which contains all the internal data for a user as well as methods for normal actions on that data, like get_age() or whatever. It also contains any persistence (db) or other features.

That's the Model.

I'm still fuzzy on what makes the View and Control.

My best guess is that View is a bunch of formatting functions, and Control uses both the Method object and the View functions to give you web pages. Am I right?

For example, I want a list of everyone who has blue hair. The control might be bluehair.pl, a user callable CGI. It would instantiate a bunch of User (or Method::User) objects and use User->has_blue_hair() to pick the ones that had blue hair. Then maybe it would use CGI.pm to present the View.

Warmer? Still missing it?

Thanks

-Pileofrogs

[Joost]

My best guess is that View is a bunch of formatting functions, and Control uses both the Method object and the View functions to give you web pages. Am I right?

You're quite right.

If I'm not mistaken, in the original MVC design, the controller is responsible for setting up the view and connecting it to the model, and after that the View and the Model work mostly by themselves. But since web based applications behave differently from typical GUI applications, what tends to happen is subtly different:

   Browser           View              Controller      Model
    .                 .                 .               .
    . HTTP Request    .                 .               .
    +---------------------------------->+               .
    |                 .                 | update model  .
    |                 .                 +-------------->+
    |                 .                 |               |
    |                 .                 | return status |
    |                 .                 +<--------------+
    |                 .     select view |               .
    |                 +<----------------+               .
    |                 |                 .               .
    |                 | query state     .               .
    |                 +-------------------------------->+
    |                 |                 .               |
    |                 |                 .  return state |
    |                 +<--------------------------------+
    |   HTTP Response |                 .               .
    +<----------------+                 .               .
    .                 .                 .               .

(see also http://zeekat.nl/joost/mvc-web/index.html)

Basically, the controller interprets the (http) requests as model actions/queries and then passes (parts of) the model* to the appropriate view (which is selected by the controller and does nothing more than display part of the model).

* By model here I mean all of the objects and classes that make up the API of whatever is being manipulated by the program - i.e. a database, sensors, a tv-card, whatever.

For example, I want a list of everyone who has blue hair. The control might be bluehair.pl, a user callable CGI. It would instantiate a bunch of User (or Method::User) objects and use User->has_blue_hair() to pick the ones that had blue hair. Then maybe it would use CGI.pm to present the View.

Yes. You've got the basic seperations right. But in most MVC frameworks in use today you would probably put most of the specifics of bluehair.pl (which might be VERY little, if you're using a good framework) in a subclass of the generic controller class and you'd use a templating system to generate the views.

Also, if you're using a relational database, it's a lot more efficient to use an SQL query (probably implemented as a Model::User class method, and likely generated by an OO-relational library) to select a list of blue haired people instead of iterating through all users in the database one by one.

updated: minor corrections.

[perrin]

Ideally, the controller wouldn't do much here. It would read the web request, see that the action requested is a search, read the parameter hair_color=blue from the query string, and then call a method like this:

my @users = User->search(hair_color => $hair_color);

Then it would pass the @users data to a template for display.