extending PDO class

Question

Below is the db connection class I came out with so far, but I am going to improve it by extending the PDO class itself,

<?php
class database
{
    protected $connection = null;

    #make a connection
    public function __construct($hostname,$dbname,$username,$password)
    {
        try 
        {
            # MySQL with PDO_MYSQL  
            $this->connection = new PDO("mysql:host=$hostname;dbname=$dbname", $username, $password);
            $this->connection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); 
        }
        catch (PDOException $e) 
        {
            $this->connection = null;
            die($e->getMessage());
        }
    }

    #get the number of rows in a result
    public function num_rows($query)
    {
        # create a prepared statement
        $stmt = $this->connection->prepare($query);

        if($stmt) 
        {
            # execute query 
            $stmt->execute();

            return $stmt->rowCount();
        } 
        else
        {
            return self::get_error();
        }
    }

    #display error
    public function get_error() 
    {
        $this->connection->errorInfo();
    }

    # closes the database connection when object is destroyed.
    public function __destruct()
    {
        $this->connection = null;
    }
}
?>

extended class,

class database extends PDO
{

    #make a connection
    public function __construct($hostname,$dbname,$username,$password)
    {
        parent::__construct($hostname,$dbname,$username,$password);

        try 
        { 
            $this->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); 
        }
        catch (PDOException $e) 
        {
            die($e->getMessage());
        }
    }

    #get the number of rows in a result
    public function num_rows($query)
    {
        # create a prepared statement
        $stmt = parent::prepare($query);

        if($stmt) 
        {
            # execute query 
            $stmt->execute();

            return $stmt->rowCount();
        } 
        else
        {
            return self::get_error();
        }
    }

    #display error
    public function get_error() 
    {
        $this->connection->errorInfo();
    }

    # closes the database connection when object is destroyed.
    public function __destruct()
    {
        $this->connection = null;
    }
}

This is how I instantiate the class,

# the host used to access DB
define('DB_HOST', 'localhost');

# the username used to access DB
define('DB_USER', 'root');

# the password for the username
define('DB_PASS', 'xxx');

# the name of your databse 
define('DB_NAME', 'db_2011'); 

include 'class_database.php';

$connection = new database(DB_HOST,DB_NAME,DB_USER,DB_PASS);
$sql = "
    SELECT *
    FROM root_contacts_cfm
    ORDER BY cnt_id DESC
    ";

$connection->num_rows($sql);

But I have errors when I call this extended pdo class,

Warning: PDO::__construct() expects parameter 4 to be array, string given in C:\wamp\www\xx\class_database.php on line xx

Fatal error: Call to a member function setAttribute() on a non-object in C:\wamp\www\xx\class_database.php on line xx

I have done some research online, I found this basic structure of extending pdo but I dont understand it...

class myPDO extends PDO
{
   public function __construct($dsn, 
                               $username=null, 
                               $password=null, 
                               $driver_options=null)
   {
      parent::__construct($dsn, $username, $password, $driver_options);
   }

   public function query($query)
   {
      $result = parent::query($query);
      // do other stuff you want to do here, then...
      return($result);
   }
}

What is $dsn variable for? How can I pass my $hostname variable into extended pdo class?

Another questions: How can I make a method for displaying error in the extended pdo class? How can I close the connection in the extended pdo class?

It is so difficult to move from mysqli to pdo!

Thanks.

Visayan

Looking at what you have written, you really don't need to extend the PDO class. You are only making it harder than it needs to be. – Eckert

is extending pdo a bad thing? I had an independent mysqli class before but I was told better off extending mysqli so I thought it must be the same as pdo?? – Visayan

You don't need to rewrite the constructor btw. – Personable

Answer 1

$dsn is data source name. It handles your hostname for you. You use it like this:

$dsn = 'mysql:dbname=YOUR_DB_NAME;host=YOUR_HOSTNAME'

With the line $this->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); You have set exceptions to be raised when errors occur (which I like), so in your extended class you can handle errors in exception handlers. If you had a method called getAssoc in your extended PDO class then it would look like this:

/// Get an associative array of results for the sql.
public function getAssoc($sql, $params=array())
{
   try
   {
      $stmt = $this->prepare($sql);
      $params = is_array($params) ? $params : array($params);
      $stmt->execute($params);

      return $stmt->fetchAll(PDO::FETCH_ASSOC);
   }
   catch (Exception $e)
   {
      // Echo the error or Re-throw it to catch it higher up where you have more
      // information on where it occurred in your program.
      // e.g echo 'Error: ' . $e->getMessage(); 

      throw new Exception(
            __METHOD__ . 'Exception Raised for sql: ' . var_export($sql, true) .
            ' Params: ' . var_export($params, true) .
            ' Error_Info: ' . var_export($this->errorInfo(), true),
            0,
            $e);
   }
}

Sidekick

thanks Paul. could you please give me an example code you can handle errors in exception handlers...? – Visayan

Answer 2

I would concentrate on what the class needs to do rather than trying to re write the PDO. I had the same idea because i though it would simplify and stream line the code but it doesn't. You end up spending more time working out how to indirectly interface with the PDO.

Alisealisen