Question

I hava a class called DBhelper, and now I created a new class called UserManager.
I need the UserManager have functions like GetUserId() and CheckValidation().So I require the DBhelper for those database actions. But I found it doesn’t work like this:

require_once('DBhelper.php');
class User{
  public $databaseHelper = new DBhelper();//syntax error
  public $DB = $databaseHelper->connectDB();//syntax error

  public function GetUserId(){
    $this->databasesHelper->RunSql();//syntax error
    ...
  }
  public function CheckValidation(){
    $this->databasesHelper->RunSql();//syntax error
    ...
  }
}

Please halp me, I have searched the internet for long time. thanks.

Answer 1

Try something like this, it uses the dependency injection design pattern.

class User {
    private $db;
    public function __construct(DBHelper $db) {
         $this->db = $db->connectDB();
    }

    public function GetUserId(){
        $this->db->RunSql();
    }

}

Here is how you instantiate it:

// Assuming: require( 'DBhelper.php');
$dbh = new DBHelper();
$user = new User( $dbh);

Also, to touch on your errors, these are errors (note they’re not syntax errors, since they are syntactically correct):

public $databaseHelper = new DBhelper();//syntax error
public $DB = $databaseHelper->connectDB();//syntax error

Because you cannot initialize member variables to non-static values. So, since the values are not known at compile time, it is an error.

Similarly, these calls:

$this->databasesHelper->RunSql();//syntax error

Are invalid because $databasesHelper was never instantiated with a proper object.