PDO连接未按预期工作

Question

I think this is mostly because I'm new to PHP OOP, but I have a quick question that I can't seem to find an answer for. Since I use the same connection information for several methods, I tired to take out the information and put them into property variables as private and static. However, when trying to make a PDO connection, this doesn't work:

class MyClass {
    private static $DSN = "mysql:host=localhost;dbname=testdb";
    private static $USR = "user";
    private static $PWD = "password";

    public static function connection() {
        $pdo = new PDO($DSN, $USR, $PWD);
        //more code
    }
}

Yet when I enter the information manually, it works fine:

class MyClass {
    public static function connection() {
        $pdo = new PDO("mysql:host=localhost;dbname=testdb", "user", "password");
        //more code
    }
}

So why doesn't using a set of properties work? I spent a few hours trying to get it to work and it just didn't, only to find out that that was the problem. I'm fine with manually connecting but I would like to know why the first solution doesn't work.

Answer 1

You need the self keyword (along with the scope resolution operator ::) to access those private static properties.

$pdo = new PDO( self::$DSN, self::$USR, self::$PWD);

Otherwise you're not referencing the correct variables.

See the manual for more information about static keywords.