Question

I have created a file name database.php and here is it’s content

<?php
#Start Session
session_start();
#Start Output Buffering
ob_start();
#Set Default TimeZone
date_default_timezone_set('Asia/Kolkata');

#Define Connection Constant
define('HOST','localhost');
define('USERNAME','user');
define('PASSWORD','pass');
define('DATABASE','database');
//Define Configuration Constant
define('DATE', date("d-F-Y/H:ia"));

#Connect to the database
try
{
    #Define Connection String Using PDO.
    $DBH = new PDO('mysql:host='.HOST.';dbname='.DATABASE,USERNAME,PASSWORD);

    #Set Error Mode to ERRMODE_EXCEPTION.
    $DBH->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
}
catch(PDOException $e)
{
    echo $e->getMessage();
    //Log Errors into a file
    file_put_contents("resources/logs/Connection-log.txt", DATE.PHP_EOL.$e->getMessage().PHP_EOL.PHP_EOL, FILE_APPEND);
}
?>

and now i have defined a PHP’s class and i have declared a method where i want to fetch some values based on the connection above. i have included the database.php file.

here is my code.

include('../../config/database.php');
class Property
{
    public function getAllCountries()
    {
        #Query Using Prepared Statement
        $STH = $DBH->query('SELECT * FROM countries');

        #Set the Fetch Mode
        $STH->setFetchMode(PDO::FETCH_ASSOC);

        $countries = array();
        while($row = $STH->fetch())
        {
            $countries[] = $row['name'];
            return $countries;
        }
    }
}
$property = new Property;
echo $property->getAllCountries();

when i initialize the class it doesn’t have any problem but when i try to call $property->getAllCountries(); method it gives me the following error.

Notice: Undefined variable: DBH in /Applications/MAMP/htdocs/kokaris/administrator/resources/library/models/class.property.php on line 8

Fatal error: Call to a member function query() on a non-object in /Applications/MAMP/htdocs/kokaris/administrator/resources/library/models/class.property.php on line 8

what is wrong with my code?

Answer 1

The problem is that $DBH is not in scope at the time of the call $DBH->query(). $DBH is in the global scope, while the call is within a function’s scope (getAllCountries). Unlike some other languages, global variables are not accessible within functions unless you specifically declare them.

The one-line workaround for this is to use the global value of $DBH within the function:

public function getAllCountries()
{
    global $DBH;

    #Query Using Prepared Statement
    $STH = $DBH->query('SELECT * FROM countries');

However, this is probably a bad idea, because you have now locked yourself in to a particular way of handling database connections. It would be better to pass the database object as a parameter to the constructor, store it in an object variable, and retrieve it when you need to use it.

class Property
{
    protected $dbh;

    public function __construct($dbh) {
        $this->dbh = $dbh;
    }

    public function getAllCountries() {
        $STH = $this->dbh->query('SELECT * FROM countries');

        [snip]
    }    
}

You would then need to initialise your class with the DB object passed as a parameter:

$property = new Property($DBH);
echo $property->getAllCountries();