PHP: Database Connection Class Constructor Method

Question

I'm new to OOP. Originally I was defining variables and assigning values to them within the class and outside of the constructor, but after an OOP lesson in Java today, I was told this is bad style and should be avoided.

Here is my original PHP database connection class that I mocked-up:

class DatabaseConnection {
    private $dbHost = "localhost";
    private $dbUser = "root";
    private $dbPass = "";
    private $dbName = "test";

    function __construct() {    
        $connection = mysql_connect($this->dbHost, $this->dbUser, $this->dbPass)
            or die("Could not connect to the database:<br />" . mysql_error());
        mysql_select_db($this->dbName, $connection) 
            or die("Database error:<br />" . mysql_error());
    }
}

Is the above considered okay? Or is the following a better way?

class DatabaseConnection {
    private $dbHost;
    private $dbUser;
    private $dbPass;
    private $dbName;

    function __construct() {
        $this->dbHost = "localhost";
        $this->dbUser = "root";
        $this->dbPass = "";
        $this->dbName = "test";

        $connection = mysql_connect($this->dbHost, $this->dbUser, $this->dbPass)
            or die("Could not connect to the database:<br />" . mysql_error());
        mysql_select_db($this->dbName, $connection) 
            or die("Database error:<br />" . mysql_error());
    }
}

What should I be focusing on to make sure I am understanding OOP correctly?

Answer 1

Well, it's not going to run quite yet. You need to change your variables so that they match your connection params:

$dbHost = "localhost";

Should be

$this->dbHost = 'localhost';

I normally don't put my login params inside of the class at all. I would pass them into the constructor when the object is created. Use an outside config file so you can actually use this class on more than one build. :)

Update::

Okay, so here are a few little OOP configuration gold-nuggets that help you build a dynamic Database class.

• Check out http://redbeanphp.com/ It will allow you to do a psuedo ORM style of data modelling. Super easy to install, and ridiculously easy to get your database up and running. http://redbeanphp.com/manual/installing

• Create a configuration file that contains things like constants, template setups, common functions, and an AUTOLOADER Configuration files are key when working in version controlled environments. :)

• Build your Database class as an abstract class http://php.net/manual/en/language.oop5.abstract.php

  abstract class Database
  {
    public function update()
    {
    }
  
    public function deactivate()
    {
    }
  
    public function destroy()
    {
    }
  
    //etc.
  }
  
  class MyAppObject extends Database
  {
  }
  

• Put all of your class files into a library folder, and then put your configuration file into that library. Now, to make your life easier you can use an autoloader function to bring your classes to life whenever you need them, without having to include any specific class. See below:

  //note: this is never explicitly instantiated
  //note: name your files like this: MyAppObject.class.php  
  function my_fancypants_autoloader( $my_class_name )
  {
    if( preg_match( "%^_(Model_)%", $my_class_name ) ) return;
    require_once( "$my_class_name.class.php" );
  }
  spl_autoload_register( 'my_fancypants_autoloader' );
  

  • Now all you have to do is include one configuration file in your .php files to access your classes.

Hope that points you in the right direction! Good luck!

Answer 2

First of all: this is pointless.

You are creating an object wrapper for the 10+ year old mysql_* function. This php extension is no longer maintained and the process of deprecation has already begun. You should not use this API for any new projects in 2012.

Instead you should learn how to use PDO or MySQLi and work with prepared statements.

That said .. lets take a look at your code:

• Constructor should receive all the parameters required for creating new instance, parameters should not be hard-coded in the class definition. What if you need to work with two databases at the same time ?
• When connection is created, it should be stored in object's scope variable. Something along the lines of $this->connection = mysql_conn.... Instead you store it in local variable, which you "loose" right after constructor is done.
• You should not use private variables for everything. They are not visible to classes which would extend your original class. Unless it is intentional, you should choose protected for this.
• The or die('..') bit most go. Do not stop the whole application if connection fails. Instead you should throw an exception, which then can be handled outside of the constructor.

Answer 3

<?php

    class config
    {
        private $host='localhost';
        private $username='root';
        private $password='';
        private $dbname='khandla';

        function __construct()
        {   
            if(mysql_connect($this->host,$this->username,$this->password))
            {
                echo "connection successfully";
            }
        }
        function db()
        {
            mysql_select_db($this->$dbname);
        }
    }

    $obj=new config();
?>

Answer 4

Here is mine and it works rather well:

class Database
{
   private static $_dbUser = 'user';
   private static $_dbPass = 'pwd';
   private static $_dbDB = 'dbname';
   private static $_dbHost = 'localhost';
   private static $_connection = NULL;

   /**
    * Constructor
    * prevents new Object creation
    */

   private function __construct(){
   }

   /**
    * Get Database connection
    * 
    * @return Mysqli
    */

   public static function getConnection() {
      if (!self::$_connection) {
     self::$_connection = @new mysqli(self::$_dbHost, self::$_dbUser, self::$_dbPass, self::$_dbDB);

         if (self::$_connection -> connect_error) {
            die('Connect Error: ' . self::$_connection->connect_error);
         }
      }
      return self::$_connection;
   }
}

By making the __construct empty, it prevents a new class being instantiated from anywhere. Then, make the function static so now all I need to do to get my connection is Database::getConnection() And this is all in an include file, in a password protected folder on the server and just included with each class file. This will also check to see if a connection is already open before attempting another one. If one is already established, it passes the open connection to the method.

Answer 5

Since your are only using them into the __construct method, you don't need them as class attributes. Only the $connection has to be kept for later use imho.

It might be much much better to not give any default values to those arguments but let them being set from the outside.

$db = new DatabaseConnection("localhost", "user", "password", "db");

They are plenty of PHP tools for that already, find them, read them and learn from that. First of all, use PDO and what is true in Java isn't always true in PHP.

Answer 6

The latter is probably better, but with an adjustment: pass some arguments to the constructor, namely the connection info.

Your first example is only useful if you've got one database connection and only if you're happy hard-coding the connection values (you shouldn't be). The second example, if you add say, a $name parameter as an argument, could be used to connect to multiple databases:

I'm new to OOP. Originally I was defining variables and assigning values to them within the class and outside of the constructor, but after an OOP lesson in Java today, I was told this is bad style and should be avoided.

class DatabaseConnection {
    private $dbHost;
    private $dbUser;
    private $dbPass;
    private $dbName;

    function __construct($config) {
        // Process the config file and dump the variables into $config
        $this->dbHost = $config['host'];
        $this->dbName = $config['name'];
        $this->dbUser = $config['user'];
        $this->dbPass = $config['pass'];

        $connection = mysql_connect($this->dbHost, $this->dbUser, $this->dbPass)
            or die("Could not connect to the database:<br />" . mysql_error());
        mysql_select_db($this->dbName, $connection) 
            or die("Database error:<br />" . mysql_error());
    }
}

So using this style, you now have a more useful class.