在PHP中包含类中心文件的方法

Question

my class user tries to access the $db object.

The problem is that the class user can't find the $db object after including it in my central file loader.inc.php . If I include the connect.php in every function/method, it works, but I want a central way to include all my classes and files.

user.class.php

class user {

        public function login($username, $password) {
            $username = $db->real_escape_string($username);
            $password = hash('sha256', $password);
            $stmt = "SELECT username, activation FROM users WHERE username='$username' AND password='$password';";
            $result = $db->query($stmt);
            $count_row = $result->num_rows;
            if ($count_row ==  1) {
                    $userdata = $result->fetch_array(MYSQLI_ASSOC);
                    if ($userdata['activation'] == 0) {
                        return false;
                    } else {
                        return true;
                    }
                } else {
                    return false;
                }
        }
}  

connect.php

require_once 'config.php';
require_once 'loader.inc.php';

$db = new mysqli(DB_HOST, DB_USER, DB_PASS, DB_NAME);
if (mysqli_connect_errno()) {
    print mysqli_connect_errno();
} else {
    $db->query("SET NAMES utf8");
}  

loader.inc.php

require_once 'connect.php';
require_once 'user.class.php'; 

I know that the include function like it's shown here isn't secure, but I use this script only for testing purposes.

Sincerely

Johannes

Answer 1

You have a variable scope problem.

    public function login($username, $password) {
        $username = $db->real_escape_string($username);
        ...

$db is not defined in the scope of the login() method.

There are several ways to solve that (like sending the database as a parameter to the method, etc.) but a common one in OOP is using dependency injection: When you instantiate a user object, you send the database object as a parameter to the constructor and set a property on the user object. Then you can use it everywhere in that class.

A simple example:

class user {
  private $db;

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

  public function login($username, $password) {
    $username = $this->db->real_escape_string($username);
    ...

Answer 2

There are 2 method for solving this. One that I recommend and one that I don't.

1. Use the global keyword.

function login($username, $password) { global $db; $db->query(...); }

2. Use dependency injection and inject into constructor of class (recommended)

   class User {

    private $db; public function __construct($db) { $this->db = $db; } public function login($username, $password) { $this->db->query(...); } 

   }

Answer 3

You don't understand the principles of object oriented programming. The classes are independent parts of code. Class (and object) can use variables and methods only defined in that class. The exceptions are static variables and methods.

<?php

    class User {
        protected $var1;
        protected $var2;
    }

In example above the class has defined only two variables and can use only these two variables. OK. So what we can do to use external variables like $db ?

In PHP, we are using Dependency Injection pattern which looks like:

<?php

    class User {
        private $connection;

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

    $user = new User($db);
    ...

If you don't want to inject $db variable always when you creating new class, you can create class DB using the Singleton anti-pattern or Laravel-like Proxy pattern .