PHP OOP - Database class (Undefined variable)

Question

Learning OOP with PHP I have created a database class, but I am getting undefined variable db_host db_name db_username and db_password. I've tried with $this->db_host which removes the undefined variable for db_host but then I get a Fatal error saying "Using $this when not on object context".

<?php
class database
{
    private $db_host = "";
    private $db_username = "";
    private $db_password = "";
    private $db_name = "";

    static function connect()
    {
        try {
            new PDO("mysql:host=" . $db_host . '; dbname=' . $db_name, $db_username, $db_password);
            setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        } catch (PDOException $db_error) {
            echo $db_error->getMessage();
        }
    }
}
?>

It has to do with your method it's static

Daan
– Daan

2015-07-23 11:25:50 +00:00
Commented Jul 23, 2015 at 11:25 — Daan
– Daan, Commented Jul 23, 2015 at 11:25

TechWisdom · Accepted Answer · 2015-07-23 12:00:11Z

1

You cannot access non static instance fields from static functions (but you can access static instance fields and functions from a non static method). Moreover, you are misusing "setAttribute" function.

You should either make your instance variables static and use self keyword:

class database
{
    private static $db_host = "...";
    private static $db_username = "...";
    private static $db_password = "...";
    private static $db_name = "...";

    public static function connect()
    {
        try {
            $dbConnection = new PDO("mysql:host=" . self::$db_host . '; dbname=' . self::$db_name, self::$db_username, self::$db_password);
            $dbConnection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        } catch (PDOException $db_error) {
            echo $db_error->getMessage();
        }
    }
}

Or, make your function non static and relate to the class variables with $this keyword:

class database
{
    private $db_host = "...";
    private $db_username = "...";
    private $db_password = "...";
    private $db_name = "...";

    public function connect()
    {
        try {
            $dbConnection = new PDO("mysql:host=" . $this->db_host . '; dbname=' . $this->db_name, $this->db_username, $this->db_password);
            $dbConnection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        } catch (PDOException $db_error) {
            echo $db_error->getMessage();
        }
    }
}

What will you do with the "dbConnection" variable? Right now it doesn't serve any purpose. You should return it, or bind another instance field with it.

edited Jul 23, 2015 at 12:00

answered Jul 23, 2015 at 11:35

TechWisdom

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4 Comments

Johnny Over a year ago

Still error: Fatal error: Using $this when not in object context. Changed to public function and used $this-> for my variables.

TechWisdom Over a year ago

Cannot be. Check you don't have a static keyword anymore, and look at my edit about "setAttribute" function.

Johnny Over a year ago

dbConnection variable is not written by me, i am not using that. But you have the answer here. Instance variable static and using self!

TechWisdom Over a year ago

Great @Johnny. I added this "dbConnection" variable because the method setAttribute belongs to the PDO object, and you should act upon this object.

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