Learn CakePHP From Novice to Professional : Part 2

Model-View-Controller

Cake enforces an MVC structure for your web applications. Basically, it effectively separates typical operations into specific areas:

MODELS :	for all your database interaction
VIEWS :	for all your output and displays
CONTROLLERS :	for all your commands/scripts for input and program flow

The typical PHP application mixes each of these three functions in the same code, making it difficult to maintain and debug.



This is the typical flow for PHP scripting (see Figure 1-1):

1. The client sends a request to a PHP script by typing a URL or clicking a link of some kind.


2. The script processes the data and then sends the database requests directly to the database.


3. The script receives any database output and processes the data.


4. The script generates output and forwards it to the client’s browser.

In short, everything is contained in one PHP script. By using the include() function, developers strip out common functions into other external files, which makes it possible to reduce redundancy. The most complex PHP applications use objects that can be called anywhere in the application and modified depending on the variables and settings passed to them. Developers, when using objects and classes, can structure the application in numerous ways.

MVC improves upon the typical PHP flow and is an effective technique for making class objects available over the whole application. The main goal behind MVC is to make sure that each function of the application is written once and only once, thus streamlining code by reducing redundancy. Cake accomplishes this goal by not only providing the resources to make MVC possible but also by using a consistent method for where to store operations in the application. Simply naming your own files a certain way allows Cake to piece together the various resources without using any code specifications.



MVC can vary depending on the framework with which you’re working, but generally it works as follows (see Figure 1-2):

1. The client sends a page request to the application, either by typing a URL or by clicking a link of some kind. By convention, a typical URL is usually structured like this:
   

   http://{Domain}.com/{Application}/{Controller}/{Action}/{Parameter 1, etc.}

   
   


2. The dispatcher script parses the URL structure and determines which controller to execute. It also passes along any actions and parameters to the controller.


3. The function in the controller may need to handle more data than just the parameters forwarded by the dispatcher. It will send database requests to the model script.


4. The model script determines how to interact with the database using the requests submitted by the controller. It may run queries with the database and do all sorts of handy data-sorting instructions.


5. Once the model has pulled any data from or sent data to the database, it returns its output to the controller.


6. The controller processes the data and outputs to the view file.


7. The view adds any design or display data to the controller output and sends its output to the client’s browser.

The benefit of using MVC to develop web sites is that repeated functions or tasks can be separated, thus allowing for quicker edits. It can even help in debugging. Say an error keeps occurring during the interaction with the database. Usually the problem will be somewhere in a model. Knowing that all database interactions occur in just one place makes it easier to solve problems.