PHP OOP - Uncaught Error: Using $this when not in object context

Question

So I have a Database class with a function like this:

public function sql($sql) {
    $result = $this->connection->query($sql);
    return $result;
}

But it returns the error:

Fatal error: Uncaught Error: Using $this when not in object context

But I don't get it why I get this error, I've looked al around the internet, but nobody seems to have this exact problem.

This is my full database class:

namespace Core;

require_once ("../config.php");

class DB {

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

    public function connection() {
        $this->connection = new \mysqli(DB_HOST, DB_USER, DB_PASS, DB_NAME);

        if ($this->connection->connect_error) {
            die("Database fout");
        }
    }

    public function sql($sql) {
        $result = $this->connection->query($sql);
        return $result;
    }
}

Then I call it like so:

DB::sql('SELECT * FROM `users`');

But then I get the error. :/

Sigh. What does `DB::sql` express? It is a _static_ call to a class method, it does _not_ use an object... — arkascha, Jan 10 '17 at 08:47
Always ask yourself that question: what does `$this` actually point to? Can you answer that? — arkascha, Jan 10 '17 at 08:49

score 2 · Accepted Answer · edited Jan 10 '17 at 12:49

DB::sql('SELECT * FROM `users`');

This is static function call method and in static function you can't use $this You need to call like

$database = new DB();
$sql = $database->sql('SELECT * FROM `users`')

In that case according to your comment your class should look like

<?php
namespace Core;

require_once ("../config.php");

class DB
{
    public static $connection;

    public static function connection()
    {
        self::$connection = new \mysqli(DB_HOST, DB_USER, DB_PASS, DB_NAME);
        if (self::$connection->connect_error) {
            die("Database fout");
        }
    }
    public static function sql($sql)
    {
        $result = self::$connection->query($sql);
        return $result;
    }
}
DB::connection();

Okay, thanks. but what if I want to call my function like `DB::sql` how would I have to modify my DB class? — Luuk Wuijster, Jan 10 '17 at 08:56

PHP OOP - Uncaught Error: Using $this when not in object context

1 Answers1