无法在PHP注册表单中连接到数据库

Question

我一直在用PHP编写注册表单。完成代码后，它运行完美，没有任何错误（它表示“refistration not successfull”）但是用户信息没有存储在我创建的数据库中。完整代码如下：

Process.php：

<?php

class db{

    public $host = "localhost";
    public $user = "root";
    public $pass = "";
    public $db_name = "oop";

    public $link;

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

    private function connect(){
    $this->link = new mysqli($this->host,$this->user,$this->pass,$this->db_name);
    }

    public function insert($query){
        $result = $this->link->query($query);

        if($result){
            echo "<center><h2>Registration successful</h2></center>";
        }
        else{
            echo "<center><h2>Registration not successful</h2></center>";
        }
    }
}

?>

form.php的：

<h2>Registration Form</h2>
<form method="post" action ="form.php">
    <label>User Name</label>
    <input type = "text" name = "name" placeholder="Enter user name" required="required"></input>

    <label>User Email</label>
    <input type = "text" name = "email" placeholder="Enter user Email" required="required"></input>

    <label> User Password</label>
    <input type = "password" name = "pass" placeholder="Enter password" required ="required"></input>

    <input type = "submit" name = "signup" value = "Sign Up"></input>
</form>

<?php
include "process.php";

$db = new db();

if(isset($_POST['signup'])) {

    $user = $_POST['name'];
    $email = $_POST['email'];
    $pass = $_POST['pass'];

    $query = "INSERT INTO users(user_name,user_email,user_pass) VALUES('$user','$email','$pass')";

    $db->insert($query);  
 }
?>

帮助解决这个问题。