Model-View-Controller

From CunningPlans

Model, View, Controller is a pattern for separating the major areas of functionality of a software project. Like other application frameworks, Baldrick enables and encourages this style of programming.

For a detailed introduction, see the Wikipedia article Model-view-controller.

Contents 1 MVC in Baldrick 1.1 Model 1.2 Controller 1.3 View 2 Example

[edit] MVC in Baldrick

[edit] Model

The Model consists of the Module author's classes to represent the logic of the application. These classes (not part of Baldrick) are such things as a Shopping Cart (and cart items), Message Board (and board postings), etc.

One simple Model used by most applications is an entity that is loaded from a database record, modified, and saved back to the database. Baldrick::SpecialTurnip provides one implementation of this.

[edit] Controller

The Controller is your Module's subclass of Baldrick::Dogsbody. These classes are loaded as needed by Baldrick::App, and the requests dispatched to each. The run() method of Baldrick::Dogsbody then invokes the appropriate handle function of the Dogsbody, based on the user's command.

[edit] View

The View is provided by the TemplateAdapter family of classes. These produce output (web pages, files, email) using any of several template languages - currently Template Toolkit and Text::Template are supported. To make a "Model" object available to the template system, use the addObject() method of the TemplateAdapter.

[edit] Example

The Dogsbody class (a Controller) that implements a Module ties the three types of components together. This generally happens in the handle functions.

package MyCart::MyAppDogsbody;

sub handleAddToCart
{
    my ($self, %args) = @_;

    my $request = $self->getRequest();

    # set up the Model object.
    my $cart = new MyCart::ShoppingCart();
    $cart->load( session => $self->getSession() );

    # Manipulate it.
    my $rc = $cart->add(productid => $request->get("productid"));

    # send one of several Views
    if ($rc < 0)  # ERROR
    {
        $self->sendOutput(error => $cart->getError());
    } else {
        # Make model available to view
        $self->getOut()->addObject($cart, "cart");
        $self->getOut()->addObject($cart->getItemAdded(), "newitem");

        # and send it to user.
        $self->sendOutput(template => "added-item");
    }
}