Using PDO database class within other PHP classes

Question

I have a database class that uses PDO. Here's a portion example of it:

class db {
private $host;
private $username;
private $password;
private $con;
    private $pdo;

public function __construct( $database = "dnname" )
{
    $this->host = "localhost";
    $this->username = "username";
    $this->password = "pass";
            $conStr = "host={$this->host};dbname={$database}";
            try {
                $this->pdo = new PDO( "mysql:$conStr", $this->username, $this->password );
                $this->pdo->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );
            }
            catch( PDOException $e ) {
                echo "error ". $e->getMessage();
            }
}

public function fetch_single_row($sql, $data)
{
    if( $data !== null )
        $data = array_values( $data ); // Incase it's an associative array
    $sel = $this->pdo->prepare( $sql );
    $sel->execute( $data );
    $sel->setFetchMode( PDO::FETCH_OBJ );
    $obj = $sel->fetch();
    return $obj;
}

I would like to use this class and its functions (it has more than I've included) inside other classes.

I have tried many many different things, but the only thing that works so far is starting a new instance of db in every new class which I think is bad practice. For instance:

class cms {
   function cms(){
       $this->db = new db();
   }

   function is_admin($id) {
    if($this->db->fetch_single_row("SELECT id FROM user WHERE id = ? LIMIT 1", array($id))){
        return true;
    } else {
        return false;
    }
}

in my index.php, I include these classes and use them:

include("db.class.php");
include("cms.class.php");

$cms = new cms();

if($cms->is_admin($id)){
   //code here
}

What is the correct way to accomplish this?

Should your db class's variables be static? It would alleviate most, if not all, performance issues regarding multiple instantiation. In fact, you could just not instantiate a new instance of your db class, but use static functions of your class. — Waleed Khan, Jul 22 '12 at 04:26
__Construct cannot be static, according to php error reporting :) — Brandon Fredericksen, Jul 22 '12 at 04:32
Well, since it's static, you'll only ever need to call any constructing code once. Therefore, explicitly calling a pseudo-constructor after defining the class will do it for you. (But I agree with `__construct` not being static.) — Waleed Khan, Jul 22 '12 at 04:34
I apologize, I am unsure what you mean. Do you mean changing all the functions in my db class to static, except for the __construct()? — Brandon Fredericksen, Jul 22 '12 at 04:37

Kris · Accepted Answer · 2012-07-22T05:50:48.850

4

Take a look into the Singleton Design Pattern, it works great for a DB class

I used to use a class like this for quite a while

   abstract class DB
   {

    protected static $instance;

    protected $db;

    protected static $host = 'host';
    protected static $user = 'user';
    protected static $pass = 'pass';
    protected static $database;

    public static function getInstance()
    {
        if (!isset(self::$instance)) self::$instance = new static();

        return self::$instance;
    }

    protected function __construct()
    {
        $this->db = new PDO(sprintf('mysql:host=%s;dbname=%s', static::$host, static::$database), static::$user, static::$pass);
        $this->db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    }

    public static function db()
    {
        return static::getInstance()->db;
    }

    public function fetch_single_row($sql, $data)
    {
        if( $data !== null )
            $data = array_values( $data ); // Incase it's an associative array
        $sel = self::db()->prepare( $sql );
        $sel->execute( $data );
        $sel->setFetchMode( PDO::FETCH_OBJ );
        $obj = $sel->fetch();
        return $obj;
    }
}

I would then extend that class for each different database I would need to connect to

class Main extends DB
{
    protected static $database = 'db';
}

You can then use the class like this

$db = Main::getInstance();
$obj = $db->fetch_single_row($sql, $data);

edited Jul 22 '12 at 05:50

answered Jul 22 '12 at 05:10

Kris

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Whenever you need an instance of the database connection in your application, just call `$db = Main::getInstance();` and continue using `$db` to perform queries – galymzhan Jul 22 '12 at 05:12
There seems to be a problem with this line: if (!isset(self::$instance)) self::$instance = new static(); – Brandon Fredericksen Jul 22 '12 at 05:23
I get `FATAL ERROR: Call to protected method db::getInstance() from context 'cms' ` when trying to call `$this->db = db::getInstance();` inside my cms class – Brandon Fredericksen Jul 22 '12 at 05:29
Which version of PHP are you using? The static keyword is late static binding and is available in php 5.3+. So if you are using an older version, then a quick fix is by not makign it an abstract class – Kris Jul 22 '12 at 05:30
sorry, make the getInstance function public. I have updated my code – Kris Jul 22 '12 at 05:30
after you make the getInstance function public it should work fine. I just tested it – Kris Jul 22 '12 at 05:41
I am extremely grateful for your help, but I cannot get passed the php errors. Could you provide example of usage in another class? such as my example above? Also the line `if (!isset(self::$instance)) self::$instance = new static();` gives errors in dreamweaver. Is it supposed to be `if (!isset(self::$instance)) self::$instance = new db();`? – Brandon Fredericksen Jul 22 '12 at 05:46
I updated my code providing an example. I put your function in the base class and shown how to use it. I tested the code and it works fine. No that line is suppose to be the way it is, this is late static binding. I just ran the code myself and it worked fine – Kris Jul 22 '12 at 05:52

Using PDO database class within other PHP classes

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