Creating a CRUD Application with PHP

Lesson 4: Optimizing the Code with Classes and Objects

In this lesson you optimize the code to facilitate maintaining it in the future. This affects the files createNewWisher.php and wishlist.php. Additionally, a new file called db.php is created.

Your application's code contains several similar blocks with queries to the database. To make the code easier to read and maintain in the future, you can extract these blocks, implement them as functions of a separate class called WishDB, and place WishDB in db.php. Afterwards you can include the db.php file in any PHP file and use any function from WishDB without code duplication. Such an approach ensures that any changes to queries or functions will be made in one place and you will not have to parse the entire application code.

When you use a function from WishDB, you do not change the value of any of WishDB's variables. Instead, you use the WishDB class as a blueprint for creating an object of WishDB, and you change the values of variables in that object. When you finish working with that object, it is destroyed. Because the values of the WishDB class itself are never changed, you can reuse the class an unlimited number of times. In some cases you may want to have multiple instances of a class in existance at the same time, and in other cases you may prefer a "singleton" class, where you only have one instance in existance at any one time. WishDB in this tutorial is a singleton class.

Note that the term for creating an object of a class is "instantiating" that class, and that another word for an object is an "instance" of a class. The general term for programming with classes and objects is "object-oriented programming," or OOP. PHP 5 uses a sophisticated OOP model. See php.net for more information.

The current document is a part of the Creating a CRUD Application in the NetBeans IDE for PHP tutorial.

Lessons in this tutorial:

0. Creating a CRUD Application with PHP - Main page
1. Creating a MySQL Database
2. Designing the Application. Reading from the Database
3. Creating a New Application User
4. => Optimizing the Code
5. Adding Security. Implementing Application User Logon
6. Writing a New Entry into the Database
7. Updating and Deleting Entries in the Database
8. Making the Application Look Better Using the CSS Technology
9. Deploying the Application on a Remote Web Server

Contents of this lesson

• Application Source Code from the Previous Lesson
• Creating the db.php File
• Creating the WishDB Class
• Instantiating the WishDB Class
• Adding a Constructor to the WishDB Class
• Functions in the WishDB Class
  • Function get_wisher_id_by_name
  • Function get_wishes_by_wisher_id
  • Function create_wisher
• Refactoring Your Application Code
  • Refactoring the wishlist.php File
  • Refactoring the createNewWisher.php File
• Application Source Code after the Current Lesson Is Completed

Application Source Code from the Previous Lesson

Click here to download the source code that reflects the project state after the previous lesson is completed.

Creating the db.php File

Create a new subfolder in the Source Files folder. Name the folder Includes. Create a new file named db.php and place it in Includes. Later you can add more files to this folder that will be included in other PHP files.

To create db.php in a new folder:

1. Click the right mouse button on the Source files node and choose New > Folder from the context menu. The New Folder dialog opens.
2. In the Folder Name field, type Includes. Then click Finish.
3. Click the right mouse button on the Includes node and choose New > PHP File from the context menu. The New PHP File dialog opens.
4. In the File Name field, type db. Then click Finish.

Creating the WishDB Class

To create the WishDB class, you need to initialize the variables of the class and implement a constructor of the class.

<?php
class WishDB {



// single instance of self shared among all instances
private static $instance = null;



// db connection config vars
private $user = "phpuser";
private $pass = "!phpuser";
private $dbName = "wishlist";
private $dbHost = "localhost";
private $con = null;




}
        ?>        

The object (or "instance") of the WishDB class is stored in the $instance variable. In the code above, it is declared null. You also declare database configuration variables for storing the name and password of the database owner (user), the name of the database, and the database host. All these variable declarations are "private," meaning that the initial values in the declarations cannot be accessed from outside the WishDB class (See php.net).

Instantiating the WishDB class

For other PHP files to use functions in the WishDB class, these PHP files need to call a function that creates an object of ("instantiates") the WishDB class. WishDB is designed as a singleton class, meaning that only one instance of the class is in existance at any one time. It is therefore useful to prevent any external instantiation of WishDB, which could create duplicate instances.

Inside the WishDB class, type or paste the following code:

 //This method must be static, and must return an instance of the object if the object
 //does not already exist.
 public static function getInstance() {
   if (!self::$instance instanceof self) {
     self::$instance = new self;
   }
   return self::$instance;
 }

 // The clone and wakeup methods prevents external instantiation of copies of the Singleton class,
 // thus eliminating the possibility of duplicate objects.
 public function __clone() {
   trigger_error('Clone is not allowed.', E_USER_ERROR);
 }
 public function __wakeup() {
   trigger_error('Deserializing is not allowed.', E_USER_ERROR);
        }

The getInstance function is "public" and "static." "Public" means that it can be freely accessed from outside the class. "Static" means that the function is available even when the class has not been instantiated. As the getInstance function is called to instantiate the class, it must be static.

The double-colon (::), called the Scope Resolution Operator, and the self keyword are used to access static functions. Self is used from within the class definition to refer to the class itself. When the double-colon is used from outside the class definition, the name of the class is used instead of self. See php.net on the Scope Resolution Operator.

Adding a Constructor to the WishDB Class

// private constructor
private function __construct() {
   $this->con = mysql_connect($this->dbHost, $this->user, $this->pass)
           or die ("Could not connect to db: " . mysql_error());
   mysql_query("SET NAMES 'utf8'");
   mysql_select_db($this->dbName, $this->con)
           or die ("Could not select db: " . mysql_error());
        }

Functions in the WishDB Class

In this lesson you will implement the following functions of the WishDB class:

• get_wisher_id_by_name for retrieving the id of a wisher based on the wisher's name
• get_wishes_by_wisher_id for retrieving a list of wishes of the wisher with a specific id
• create_wisher for adding a new wisher record to the table wishers

public function get_wisher_id_by_name ($name) {
    $name = mysql_real_escape_string($name);
    $result = mysql_query("SELECT id FROM wishers WHERE name = '" . $name . "'");
    if (mysql_num_rows($result) > 0)
       return mysql_result($result, 0);  
    else
       return null;
            }

public function get_wishes_by_wisher_id($id) {
    return mysql_query("SELECT * FROM wishes WHERE wisher_id=" . $id);
}

public function create_wisher ($name, $password){
    $name = mysql_real_escape_string($name);
    $password = mysql_real_escape_string($password);
    mysql_query("INSERT INTO wishers (name, password) VALUES ('" . $name . "', '" . $password . "')");
            }

Refactoring Your Application Code

Now that you have a separate class for working with the database, you can replace duplicated blocks with calls to the relevant functions from this class. This will help avoid misspelling and inconsistency in the future. Code optimization that does not affect the functionality is called refactoring.

Application Source Code after the Current Lesson Is Completed

Click here to download the source code that reflects the project state after the lesson is completed.

Next Steps

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Useful Links

Learn more about using classes in PHP:

• Classes and Objects

Learn more about refactoring PHP code:

• Seven Steps To Better PHP Code
• PHP Refactoring

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