AJAX and PHP

Server-Side Techniques with PHP and MySQL
• In classes, you can implement two special methods called the constructor and
destructor. The constructor is called __construct(), and is executed automatically
when you create new instances of a class. The constructor is useful when you have
code that initializes various class members, because you can rely on it always
executing as soon as a new object of the class is created.
• The destructor is named __destruct(), and is called automatically when the object
is destroyed. Destructors are very useful for doing housekeeping work. In most
examples, we will close the database connection in the destructor, ensuring that we
don't leave any database connections open, consuming unnecessary resources.
• It is true that it may be a bit better for performance to create the database connection
just before needing it, instead of the class constructor, and to close it right after using
it, instead of the class destructor. However, we choose to use the constructor and
destructor because we get cleaner code where we are less likely to cause errors by
forgetting to close the connection, for example.
When referring to any class member, you must specify the object it is a part of. If you want
to access a local class member, you must use the special $this object, that refers to the current
class instance.
The public interface of a class consists of its public members, which are accessible from the
outside, and can be used by programs that create instances of the class. Class members can be
public, private, or protected. Private members can be used only internally by the class, and
protected members can be used by derived classes.
Separating the various layers of functionality of an application is important, because it allows you
to build flexible and extensible applications that can be easily updated when necessary. In Cristian
Darie and Mihai Bucica's PHP e-commerce books, you even learn how to use a templating engine
called Smarty that allows you to further separate presentation logic from the HTML template, so
that designers are not bothered with the programming part of the site.
When preparing the design of your code, keep in mind is that the power, flexibility, and
scalability of the architecture is directly proportional to the time you invest in designing it
and writing the foundation code. Reference to these issues is available for free download
at http:// ajaxphp.packtpub.com/ajax/
For this final exercise, we will build a simple but complete AJAX application called friendly, that
implements many of the practices and techniques shown so far. The application will have a
standard structure, composed of these files:
• index.html is the file loaded initially by the user. It contains the JavaScript code that
makes asynchronous requests to friendly.php.
• friendly.css is the file containing the CSS styles to be used in the application.
• friendly.js is the JavaScript file loaded together with index.html on the client
side. It makes asynchronous requests to a PHP script called friendly.php to
perform various functionality required to support the rich client interface.
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