PHP-PDO连接类-无法访问

Question

I'm currently writing my first PHP application using OOP and PDO. In doing so I'm working on a connection class so that I can initiate a database connection when needed. I believe the terms for the way I am doing it is dependency injection.

I currently have an error when trying to access the connection.

This is my connection class:

class db{

    private $host = '';
    private $dbname = '';
    private $username = '';
    private $password ='';  

    public $con = '';

    function __construct(){

        $this->connect();   

    }

    function connect(){

        try{

            $this->con = new PDO("mysql:host=$this->host;dbname=$this->dbname",$this->username, $this->password);
            $this->con->setAttribute(PDO::ATTR_ERRMODE,PDO::ERRMODE_EXCEPTION);

        }catch(PDOException $e){

            echo 'We have a problem!';

        }
    }
}

And this is how I am trying to call it inside of other classes.

    private $con;

    public function __construct(db $con) {
        $this->con = $con;
    }

However this is the error I receive when trying to run it.

    Catchable fatal error: Argument 1 passed to users::__construct() must be an instance of db, none given.

Any advice on what I am doing incorrectly would be much appreciated.

Answer 1

You will need to first create your DB instance and pass it to the constructor of your 'Other' class

$db = new DB();
$class = new OtherClass($db);

Apart from that, there are other issues:

The DB class constructor did not assign values to the database name, user and password etc. One way of doing it is to pass those settings to the constructor of DB and assign the values to the private properties.

class DB{

    private $host = '';
    private $dbname = '';
    private $username = '';
    private $password ='';

    public $con = '';

    function __construct($host, $dbname, $username, $password){

        $this->host = $host;
        $this->dbname = $dbname;
        $this->username = $username;
        $this->password = $password;
        $this->connect();

    }

    function connect(){

        try{

            $this->con = new PDO("mysql:host=$this->host;dbname=$this->dbname",$this->username, $this->password);
            $this->con->setAttribute(PDO::ATTR_ERRMODE,PDO::ERRMODE_EXCEPTION);

        }catch(PDOException $e){

            echo 'We have a problem!';

        }
    }
}