MVC design

It's common enough at this point to jump in and start cranking out code based on what the application is intended to do. A login page, a database, registration — BAM! Simple enough. And it usually is. Until you want to change how it looks, how it interacts with the database, change validation rules, or change essentially anything about the application at all. Then things start to get complicated.

CakePHP is designed to make writing the application as easy as possible, while giving you something you can maintain long-term. The tutorial will show you how to build Tor using the MVC design pattern. CakePHP will show you how it can be easy. You'll see for yourself why it makes sense.

The MVC design pattern breaks an application into three distinct layers: Data management, UI and Logic, respectively. MVC was first described in the book Design Patterns: Elements of Reusable Object-Oriented Software, also known as the "Gang Of Four" book. A full discussion of design patterns and MVC is outside the scope of this tutorial, but it will be helpful to touch on what the three pieces mean — specifically, in the CakePHP world.

Model

Users, products, prices, messages — when you boil it all down, it's all just data. You make sure the data is what you want, it goes into a database, then you have to get it back out. It will be useful for all the data-handling aspects of Tor to live in one place. That where model comes in.

Model is primarily concerned with handling data. Getting data from a database, inserting data into a database, validating data — all of this takes place within the model.

An individual model typically is used to access a specific table in the database. Generally, a model will associate to a database table if the table name is a plural form of the model name. For example, a Product model will, by default, associate to a Products table. All user-defined models will extend the CakePHP AppModel class.

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The user model

Having created a users table for Tor, you will need a user model to interact with the table. The user model will save your user data, get it back out of the table for you, and verify that the user data is in an acceptable format. For now, this model can be a stub. It should be created as app/models/user.php and might look something like Listing 10.

                 
<?php
class User extends AppModel
{
        var $name = 'User';
}
?>
                

Notice the line var $name = 'User';. It is accepted as best practice to specify the name of the model in $name.

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View

Being able to save, retrieve, and validate your data is pretty useless without some means of displaying the data. By putting all display and presentation code in one place, you can change the look and feel of your application without having to work around application logic and data-related code.

View is primarily concerned with formatting data for presentation to the user. The view represents any and all UI work, including all templates and HTML. CakePHP's view files are regular HTML files embedded with PHP code.

Ultimately, a view is just a page template. Usually, the view will be named after the action associated with it. For example, a display() action would normally have a display view.

Returning to the sample application, we have created a users table and a user model to interact with this table. Now we need some views. The user will need to register an account and log in to the application. This calls for a register and a login view.

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The register view

Before a user can use the Tor application, he will need to register an account. This will require a register view, which will present the registration form to the user. You should already know what kind of user information Tor is looking for — specifically, you will need to collect a username, password, e-mail address, and first and last name.

The register view should be created as app/views/users/register.ctp and might look something like that shown in Listing 11.

                    
<form action="/users/register" method="post">
<p>Please fill out the form below to register an account.</p>
<label>Username:</label><input name="username" size="40" />

<label>Password:</label><input type="password" name="password" size="40"
/>

<label>Email Address:</label><input name="email" size="40" 
maxlength="255" />

<label>First Name:</label><input name="first_name" size="40" />

<label>Last Name:</label><input name="last_name" size="40" />

<input type="submit" value="register" />
</form>
                

It is important to note that the field names are the same as the column names in your database. This will come into play when we get to the users controller. Later, when you learn a little more about Cake and see how Cake Helpers work, you will rewrite this page completely, but for now this page is regular HTML, just like you have probably always written.

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Controller

With data handling all contained within in the model, and the presentation layer all contained within the view, the rest of the application is going to live in the controller. This is where the application 'does' things — logic, decision-making, workflow, etc. The model manages your data, the view shows it to you, the controller does everything else.

The controller manages server requests. It accepts user input (URL requests, form POSTs, GET requests, etc.), applies logic where necessary, invokes models where data handling is required, and sends output through the appropriate view.

Generally, a controller will manage logic for a single model. A controller contains any number of functions, referred to as actions. An action typically applies logic and displays a view. All user-defined controllers will need to extend the CakePHP AppController class.

In Tor, you have created a users table, a user model to interact with the table, and views to present registration and login forms to the user. Those forms will submit to the users controller, invoking the register and login actions, respectively. The users controller should be created as app/controllers/users_controller.php and should start out looking something like Listing 12.

                 
<?php
class UsersController extends AppController
{
}
?>
                

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The register action

You now have a controller. But it's not doing anything yet. Before it will do anything for you, you'll have to give it some actions to perform.

Now you are getting down to the nuts and bolts. The user has filled out a form and submitted it to the application. We will cover data validation later, but for now, we will just push the registration data into the database. We do this by adding the register action to the users controller (see Listing 13).

                    
<?php
class UsersController extends AppController
{
  function register()
  {
    if (!empty($this->params['form']))
    {
      if ($this->User->save($this->params['form']))
      {
        $this->flash('Your registration information was accepted.', 
'/users/register');
      } else {
        $this->flash('There was a problem with your registration', 
'/users/register');
      }
    }
  }
}
?>

The register action starts by looking at the form ($this->params['form']) to see if it was submitted. If the form was not submitted, the action will not do anything. Once you know the form was submitted with data, the controller calls the save method on the user model, which is an extension of AppModel. The save method will, by default, look for a table that's a plural of the model itself. In this case, it is looking for a users table to go with the user model. If the table is found, the save method will turn the passed array ($this->params['form']) into an INSERT statement, using the array keys as column names and the array values as the INSERT values.

Once you know the form was submitted with data, the controller calls the save method on the user model, which is an extension of AppModel. The save method will, by default, look for a table that's a plural of the model itself. In this case, it is looking for a users table to go with the user model. If the table is found, the save method will turn the passed array ($this->params['form']) into an INSERT statement, using the array keys as column names and the array values as the INSERT values. In this case, $this->params['form'] will look like Listing 14.

                    
Array
(
    [username] => zaphod
    [password] => secret
    [email] => beeblebrox@heartofgold.hhg
    [first_name] => zaphod
    [last_name] => beeblebrox
)
                

The save method will build an INSERT statement from the rest. It would look something like Listing 15.

                 
INSERT INTO 
 users 
(username, password, email, first_name, last_name) 
VALUES
('zaphod', 'secret', 'beeblebrox@heartofgold.hhg', 'zaphod', 'beeblebrox')
                

It should now be apparent why you used the database column names in the register view for the register form field names. By doing so, you simplified the process of saving your data significantly.

To continue, if the data inserts successfully, the register action calls the Flash method. Flash presents a basic message to the user (in this case, a success or failure message) with a link away from the message (in this case, back to the register view, since nothing else has been defined.

Now that you have a user model to interface with your users table, and a register view to show a registration form, and a users controller with a register action, you can actually see your application in action.

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Try it out

All the pieces have fallen into place. It's time to bring Tor to life. Fire up your browser and jump in. Load the register view by going to http://localhost/users/register. You should see something like Figure 4.

Fill out and submit the form. You should see your success message (see Figure 5).

If you look in your database, you should see a record corresponding to your form submission, complete with a plain-text password (a terribly bad idea, which we will fix later). Try to fill out the form again, using the same information. You should see the failure message (see Figure 6).

If you are using a database that supports the UNIQUE field restraint, the registration will fail. During the creation of the users table, the username and e-mail fields were defined as UNIQUE, meaning values for those fields cannot be duplicated. CakePHP recognizes the error when the database throws it and displays an error.

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Table of contents

• Before you start
• Installation
• MVC design
• Helpers
• CakePHP data validation
• Filling in the gaps
• Summary
• Download
• Resources
• About the author

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