static and non static method to work

Question

I want to access a connexion database through PDO in a static way but I am still getting an error. This is my code :

require_once 'include/class.Settings.php';

class MonthlySums{
    protected static $dbh;
    public function __construct() {
        $user = Settings::$db['user'];
        $pass = Settings::$db['password'];
        $dsn = 'mysql:host=' . Settings::$db['host'] . ';dbname=' . Settings::$db['db'];

        try {
            self::$dbh = new PDO($dsn, $user, $pass);
        } catch(PDOException $e) {
            die("Error! : " . $e->getMessage());
        }

    }
    public static function get($init_id) {
        $sql = "SELECT `year`, `month`, `gains_monthly_sum` FROM `fxs_gain_sums` WHERE `init_id` = '$init_id'";
        $resultats = MonthlySums::$dbh->query($sql);
        var_dump($resultats);
    }

}

I have this error :

Fatal error: Call to a member function query() on a non-object in /home/public_html/gainlosssums.php on line 45

That line is : $resultats = MonthlySums::$dbh->query($sql);

How to make it work a static way ?

Answer 1

When you call a static method in a class, the constructor is not automatically invoked like when you create an instance of the class. With your code you would have to create at least one instance of the class so that the database connection would be set in your static variable. Then you would be able to call it in your desired static way.

If you still want to continue with your code, you could change it to this:

(Please note: this is the OP's modified code and I am not going into other aspects - just the result to the OP's question/problem)

require_once 'include/class.Settings.php';

class MonthlySums{
    protected static $dbh;

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

    public static function databaseLogin(){
        $user = Settings::$db['user'];
        $pass = Settings::$db['password'];
        $dsn = 'mysql:host=' . Settings::$db['host'] . ';dbname=' . Settings::$db['db'];

        try {
            self::$dbh = new PDO($dsn, $user, $pass);
        } catch(PDOException $e) {
            die("Error! : " . $e->getMessage());
        }
    }

    public static function get($init_id) {
        $sql = "SELECT `year`, `month`, `gains_monthly_sum` FROM `fxs_gain_sums` WHERE `init_id` = '$init_id'";
        $resultats = self::$dbh->query($sql);
        var_dump($resultats);
    }
}
MonthlySums::databaseLogin();

As you can see there is a new static method databaseLogin and is called right after the class declaration. This way the static variable for the database connection is set and can be used in other methods.

You now can call it this way:

MonthlySums::get(1234);

Again, this might not be best practice but a solution to your problem.