Bài giảng Web technologies and e-Services - Bài 5, Phần 2: Advanced PHP

ADVANCED PHP

1

Content

Contents

• Class

• Sessions

• PHP and MySQL

Class

3

Object oriented programming in PHP

• PHP, like most modern programming languages (C++, Java, JavaScript, etc.),

supports the creation of objects.

• Creating an object requires you to first define an object class (containing

variables and/or function definitions) and then using the “new” keyword to create

an instance of the object class. (Note that the object must be defined before you

instantiate it.)

<?php

// Assume that the "Person" object has been previously defined. . .

$x = new Person; // creates an instance of the Person class (*no* quotes)

// The object type need not be "hardcoded" into the declaration.

$object_type = 'Person';

$y = new $object_type; // equivalent to $y = new Person;

$z = new Vehicle('Jaguar','green'); // creating an object and passing

//

arguments to its constructor

?>

Defining (declaring) a class

• Use the “class” keyword which includes the class name (case-insensitive, but

otherwise following the rules for PHP identifiers). Note: The name “stdClass” is

reserved for use by the PHP interpreter.

<?php

class Person

{

var $name;

function set_name($new_name) {

$this -> name = new_name;

}

function get_name() {

return $this -> name;

}

• Use the “$this” variable when accessing properties and functions of the current

object. Inside a method this variable contains a reference to the object on which

the method was called.

Declaring a class (cont.)

• Properties and functions can be declared as “public”, “private”, “protected”

• Note that unless a property is going to be explicitly declared as public,

private, or protected, it need not be declared before being used (like

regular PHP variables).

<?php

class Person

{

protected $name;

protected $age;

function set_name($new_name) {

$this -> name = new_name;

}

function get_name() {

return $this -> name;

}

Declaring a class (cont.)

• Classes can also have their own constants defined (using the “const” keyword), can have their

own static properties and functions

• Static functions cannot access the objects properties (i.e. the variable $this is not defined inside

of a static function).

<?php

class HTMLtable {

static function start() {

echo "<table> \n";

}

static function end() {

echo "</table> \n";

}

HTMLtable::start();

?>

Accessing properties and methods

• Once you have an object, you access methods and properties (variables) of

the object using the -> notation.

<?php

$me = new Person;

$me -> set_name('Russ');

$name = $me -> get_name();

echo $me -> get_name();

$age = 36;

$me -> set_age($age);

?>

Constructors and destructors

• Constructors are methods that are (generally) used to initialize the object’s

properties with values as the object is created. Declare a constructor function in

an object by writing a function with the name __construct().

<?php

class Person {

protected $name;

protected $age;

function __construct($new_name, $new_age) {

$this -> name = $new_name;

$this -> age = $new_age;

}

// . . . other functions here . . .

}

$p = new Person('Bob Jones', 45);

$q = new Person('Hamilton Lincoln', 67);

?>

• Destructors (defined with a function name of __destructor() ) are called when an

object is destroyed

Inheritance

• Use the “extends” keyword in the class definition to define a

new class that inherits from another.

<?php

class Employee extends Person {

var $salary;

function __construct($new_name, $new_age, $new_salary); {

$this -> salary = $new_salary;

parent::__construct($new_name, $new_age); // call the constructor

//

of parent object

}

function update_salary($new_salary) {

$this -> salary = $new_salary;

}

$emp = new Employee('Dave Underwood', 25, 25000);

?>

Inheritance (cont.)

• The constructor of the parent isn’t called unless the child explicitly

references it (as in this previous case).

• You could “hard-code” the call to the parent constructor using the function

call “Person::__construct($new_name, $new_age);”

• You can use the “self” keyword to ensure that a method is called on the

current class (if a method might be subclassed), in this style

self::method();

• To check if an object is of a particular class, you can use the instanceof

operator.

More on classes

• You can also define interfaces (for which any class that uses that interface

must provide implementations of certain methods), and you can define

abstract classes or methods (that must be overridden by its children).

• The keyword “final” can be used to denote a method that cannot be

overridden by its children.

class Person {

var $name;

final function get_name() {

return $this -> name;

}

Session

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PHP sessions

• By default, HTML and web servers don’t keep track of information entered

on a page when the client’s browser opens another page.

• Sessions help solve this problem by maintaining data during a user’s visit,

and can store data

• Servers keep track of users’ sessions by using a session identifier, which

is generated by the server when a session starts and is then used by the

browser when it requests a page from the server. This session ID can be

sent through a cookie (the default behavior) or by passing the session ID

in the URL string.

• Sessions only store information temporarily

PHP sessions (cont.)

• To start a session, use the function session_start() at the beginning of your PHP script before you

store or access any data. For the session to work properly, this function needs to execute before

any other header calls or other output is sent to the browser.

<?php

session_start();

?>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<head>

<title>Session example</title>

</head>

<body>

<?php

include_once ('object.php'); // Includes definition of the Person class

$_SESSION['hello'] = 'Hello world';

echo $_SESSION['hello'] . " \n";

$_SESSION['one'] = 'one';

$_SESSION['two'] = 'two';

$me = new Person("Russ", 36, 2892700);

$_SESSION['name'] = $me->get_name();

echo "Testing " . $_SESSION['one'] .", " . $_SESSION['two'] . ", " . $me->get_number() . " . . . \n";

?>

view the output page

</body></html>

Using session variables

• Once a session variable has been defined, you can access it from other pages.

<?php

session_start();

?>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<head>

<title>Session example 2</title>

</head>

<body>

<?php

echo "Welcome to a new page ". $_SESSION['name'] "! \n";

echo "Hope you enjoy your stay! ";

?>

Back to regular HTML text...

</body>

</html>

view the output page

More on session variables

• You need to include a call to the session_start() function for each page

on which you want to access the session variables.

• A session will end once you quit the browser (unless you’ve set

appropriate cookies that will persist), or you can call the

session_destroy() function.

• The function session_unset() removes all session variables. If you

want to remove one variable, use the unset($var) function call.

• The default timeout for session files is 24 minutes. It’s possible to

change this timeout.

Deleting all session variables

<?php

session_start();

?>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<head>

<title>Session example 3</title>

</head>

<body>

<?php

echo "Deleting all session variables using session_unset(); \n";

session_unset();

echo "Now the session variables are gone. \n";

if (isset($_SESSION['name']))

{

else

{

echo $_SESSION['name'] . " \n"; }

echo "Session variable is not here.";

}

view the output page

?>

</body>

</html>

PHP and MySQL

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Putting Content into Your Database with PHP

• Connect to the database server and login (this is the PHP command to do so)

mysql_connect("host","username","password");

Host:

mysql

martin

----

• Choose the database

Database:

Username:

Password:

mysql_select_db("database");

• Send SQL queries to the server to add, delete, and modify data

mysql_query("query"); (use the exact same query string as you would

normally use in SQL, without the trailing semi-colon)

• Close the connection to the database server (to ensure the information is stored properly)

mysql_close();

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