数据库连接构造函数：私有还是公共？

Question

If I want to create a connection class, is it OK to have the __construct as private? Or that will prevent users from connecting if there is more than one user at a time? Or I'm doing something that's completely wrong and this connection class should not even exist? (using connection without specific class would be better?)

code:

   <?php

class Connection
{     
    private $host = "hostname";
    private $db_name = "somedatabase";
    private $username = "username";
    private $password = "";
    private $conn;

    private function __construct()
 {


        try {
        $this->conn = new PDO("mysql:host=" . $this->host . ";dbname=" . $this->db_name, $this->username, $this->password);
            $this->conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); 
            echo "Connected Successfully Bro";
        }
  catch(PDOException $exception) 
  {
            echo "Connection error: " . $exception->getMessage();
        }

        return $this->conn;
    }
}


?>

Answer 1

If you make the constructor private, only methods within that class will be able to create an instance of it.

That's useful if you are implementing the Singleton pattern (https://en.wikipedia.org/wiki/Singleton_pattern), or if you are creating a factory class for example.

The code you provided shows the class not having any other methods, so a private constructor is going to render the class useless if that's the case.

In short, if you need to instantiate the "Connection" class from code outside of the class itself, use a public constructor.