Use of PDO in classes

Question

I have a few classes that perform some MySQL queries and prepared statements. However, I am lost in how to incorporate my PDO object within those classes. For example, I want to do something like this:

<?php

$dbh = new PDO(...);

class Foo extends PDO {
    public $dbh;

    public function bar() {
        $this->dbh->prepare('SELECT * FROM table');
        $this->dbh->execute();

    }
}


?>

Unfortunately, it doesn't work. Can anyone suggest an elegant way to do this? Thanks for your time. Sorry I'm new to this, please leave any comments if you are unclear about anything and I'll do my best to respond!

Answer 1

You can instantiate your connection to the database in a class that implement the singleton pattern. The connection will be done once and this class will be easily accessible by all of your other objects / scripts.

i use a class called "Core" in the following example;

class Core
{
    public $dbh; // handle of the db connexion
    private static $instance;

    private function __construct()
    {
        // building data source name from config
        $dsn = 'pgsql:host=' . Config::read('db.host') .
               ';dbname='    . Config::read('db.basename') .
               ';port='      . Config::read('db.port') .
               ';connect_timeout=15';
        // getting DB user from config                
        $user = Config::read('db.user');
        // getting DB password from config                
        $password = Config::read('db.password');

        $this->dbh = new PDO($dsn, $user, $password);
    }

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

    // others global functions
}

this class take parameters from a static class called "Config" where you can store your configuration:

<?php
class Config
{
    static $confArray;

    public static function read($name)
    {
        return self::$confArray[$name];
    }

    public static function write($name, $value)
    {
        self::$confArray[$name] = $value;
    }

}

// db
Config::write('db.host', '127.0.0.1');
Config::write('db.port', '5432');
Config::write('db.basename', 'mydb');
Config::write('db.user', 'myuser');
Config::write('db.password', 'mypassword');

in all your scripts / objects you just have to get the instance of Core and then query the DB

$sql = "select login, email from users where id = :id";

try {
    $core = Core::getInstance();
    $stmt = $core->dbh->prepare($sql);
    $stmt->bindParam(':id', $this->id, PDO::PARAM_INT);

    if ($stmt->execute()) {
        $o = $stmt->fetch(PDO::FETCH_OBJ);
        // blablabla....

If you need more information about singleton look at the PHP doc http://php.net/manual/en/language.oop5.patterns.php

Answer 2

Here is a mostly complete working cut & paste example of Guillaume Boschini's answer above.

A populated DB table (MySQL):

CREATE TABLE `useraddress` (                                                                                                                                        
  `addressid` int(10) unsigned NOT NULL AUTO_INCREMENT,                                                                                                                             
  `userid` int(10) unsigned NOT NULL,                                                                                                                                               
  `addresstitle` char(100) NOT NULL,                                                                                                                        
  `streetaddressa` char(100) NOT NULL,
  `streetaddressb` char(100) DEFAULT NULL,
  `unit` char(50) DEFAULT NULL,
  `city` char(50) NOT NULL,
  `state` char(2) NOT NULL,
  `zip` int(5) NOT NULL,
  `zipplusfour` int(4) DEFAULT NULL,
  PRIMARY KEY (`addressid`),
  KEY `userid` (`userid`),
  CONSTRAINT `useraddress_fk_1` FOREIGN KEY (`userid`) REFERENCES `user` (`userid`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

In /DBLibrary/pdocore.php:

<?php

    Config::write('db.host', 'localhost');
    Config::write('db.port', '3306');
    Config::write('db.basename', 'DBName');
    Config::write('db.user', 'DBUser');
    Config::write('db.password', 'DBPassword');

    class Config {

        static $confArray;

        public static function read($name) {
            return self::$confArray[$name];
        }

        public static function write($name, $value) {
            self::$confArray[$name] = $value;
        }

    }

    class Core {
        public $dbh; // handle of the db connection
        private static $instance;

        private function __construct()  {

            // building data source name from config
            $dsn = 'mysql:host=' . Config::read('db.host') . ';dbname=' . Config::read('db.basename') . ';port=' . Config::read('db.port') .';connect_timeout=15';

            // getting DB user from config
            $user = Config::read('db.user');

            // getting DB password from config
            $password = Config::read('db.password');

            $this->dbh = new PDO($dsn, $user, $password);
            $this->dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

        }

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

        // others global functions
    }
?>

In /objectsLibrary/SYS_UserAddress.php:

<?php

    define('k_uaddress_addressid','addressid');
    define('k_uaddress_userid','userid');
    define('k_uaddress_addresstitle','addresstitle');
    define('k_uaddress_addressa','streetaddressa');
    define('k_uaddress_addressb','streetaddressb');
    define('k_uaddress_unit','unit');
    define('k_uaddress_city','city');
    define('k_uaddress_state','state');
    define('k_uaddress_zip','zip');
    define('k_uaddress_zipplusfour','zipplusfour');

    require_once '../DBLibrary/pdocore.php';

    class SYS_UserAddress {

        public $addressid;
        public $userid;
        public $addresstitle;
        public $addressa;
        public $addressb;
        public $unit;
        public $city;
        public $state;
        public $zip;
        public $zipplusfour;

        public function SYS_UserAddressByAddressId($_addressid) {

            $returnValue=FALSE;

            $query='select * from useraddress where ' . k_uaddress_addressid . '=:addressid';

            try {
                $pdoCore = Core::getInstance();
                $pdoObject = $pdoCore->dbh->prepare($query);

                $queryArray = array(':addressid'=>$_addressid);

                if ($pdoObject->execute($queryArray)) {

                    $pdoObject->setFetchMode(PDO::FETCH_ASSOC);;

                    while ($addressrow = $pdoObject->fetch()) {

                        $this->addressid=$addressrow[k_uaddress_addressid];
                        $this->userid=$addressrow[k_uaddress_userid];
                        $this->addresstitle=$addressrow[k_uaddress_addresstitle];
                        $this->addressa=$addressrow[k_uaddress_addressa];
                        $this->addressb=$addressrow[k_uaddress_addressb];
                        $this->unit=$addressrow[k_uaddress_unit];
                        $this->city=$addressrow[k_uaddress_city];
                        $this->zip=$addressrow[k_uaddress_zip];
                        $this->zipplusfour=$addressrow[k_uaddress_zipplusfour];

                    }
                    $returnValue=TRUE;
                }
            }
            catch(PDOException $pe) {
                trigger_error('Could not connect to MySQL database. ' . $pe->getMessage() , E_USER_ERROR);
            }

            return $returnValue;

        }
    }

    $test=1;
    $testAddressId=2;

    if($test>0) {

        $testAddress = new SYS_UserAddress();

        $testAddress->SYS_UserAddressByAddressId($testAddressId);

        echo '<pre>';
        echo print_r($testAddress);
        echo '</pre>';

    }

?>

The post above really helped me. This post I am making now would have gotten me to where I wanted to be faster. That is all. If anything isn't right, I'll be around to fix it.

Answer 3

$dbh isn't within the scope of Foo, do this instead:

class Foo /*extends PDO*/
{
    public $dbh;

    public function __construct()
    {
        $dbh = new PDO(/*...*/);
    }

    public function bar()
    {
        $this->dbh->prepare('SELECT * FROM table');
        return $this->dbh->execute();
    }
}

Also, Foo doesn't need to extend PDO.