PDO致命错误：在非对象上调用成员函数prepare（）

Question

I'm having this error when I try to insert data in my database. I've searched the reasons of this error and I think my codes are right and I'm not supposed to get the error. My codes are these:

config.php

<?php
class DatabaseConnection{
    public function __construct(){
        try{
        $pdo = new PDO('mysql:host=localhost;dbname=test','root',''); //'mysql:host=host;dbname=dbname','mysqluser','mysqlpassword'
        }
        catch (PDOException $e){
            exit('Database error');
        }   
    }
}
?>

functions.php

<?php

require "config.php";

class LoginRegister{
    function __construct(){
        $database= new DatabaseConnection();
    }

    public function registerUser($username,$password,$name,$email){

        global $pdo; //THIS IS THE LINE WITH ERROR
        $query=$pdo->prepare("SELECT id FROM usuarios WHERE nombre_usuario=? AND correo_e=?");
        $query->execute(array($username,$email));
        $num=$query->rowCount();

        if($num==0){
            $query = $pdo->prepare("INSERT INTO usuarios(nombre_usuario,nombre_real,password,correo_e) VALUES (?,?,?,?)");
            $query->execute(array($username,$password,$name,$email));
            return true;
        }else{
            return print "Username or E_mail in use";
        }
    }
}
?>

register.php

<?php

require_once "functions.php";
$user = new LoginRegister();
?>

...HTML CODE...

<?php
if($_SERVER['REQUEST_METHOD'] == 'POST'){
    $username=$_POST['nombre_usuario'];
    $password=$_POST['password'];
    $name=$_POST['nombre_real'];
    $email=$_POST['correo_e'];

    if(empty($username) or empty($password) or empty($name) or empty($email)){
        echo "Error... Field must not be empty";
    }else{
        $register = $user->registerUser($username,$password,$name,$email);
        if($register){
            echo "Register done <a href='login.php'>Click here</a> for login";
        }else{
            echo "Username or E_mail in use";
        }
    }
}
?>

...HTML CODE...

As you can see, I declared the variable $pdo inside the registerUser functions, besides the variables that contain the name, username, password and email are parameters of the same function.

I know this is a several times duplicated question but I cannot solve this error with the solutions in the other ones.

Answer 1

There are several problems with your code.

Two were explained in the other answer, which will make your code work (eventually it all was spoiled), but it's still wrong approach, which will connect to database as many times as many objects you have.

Change DatabaseConnection class this way

class DatabaseConnection{
    public $pdo;
    public function __construct(){
        $user = 'root';
        $pass = '';
        $dsn  = 'mysql:charset=utf8;dbname=test;host=localhost;charset=utf8';
        $opt  = array(
            PDO::ATTR_ERRMODE            => PDO::ERRMODE_EXCEPTION,
            PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
        );
        $this->pdo = new PDO($dsn, 'root', '', $opt);
    }
}

Change LoginRegister constructor this way

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

And make register.php this way

require_once "functions.php";
$db = new DatabaseConnection();
$user = new LoginRegister($db->pdo);

and then in LoginRegister use $this->db instead of $pdo all the way.

The main idea to make $db connection an external service for the application class. Otherwise it will be all the same as despised global, but just in another form.