php - PHP中的查询不会提取系统中已经存在的数据

Question

我正在尝试检查数据库中是否存在给定的电子邮件，但返回的查询为空，我不知道为什么。

我已尝试手动输入表格中记录的电子邮件地址，但仍然无法正常工作。

用户.php：

function emailExists()
{

    $query = "SELECT id, firstname, lastname, access_level, password, 
status from " . $this->table_name . " where email = ?";

    //prepare this query
    $stmt = $this->conn->prepare($query);

登录.php：

//get database connection
$database = new Database();
$db = $database->getConnection();

//initialize objects
$user = new User($db);

//check if email and password are in the database
$user->email=$_POST['email'];

//check if email exists, also get user details using this emailExists() method
$email_exists = $user->emailExists();

数据库类：

class Database{

    // specify your own database credentials
    private $host = "localhost";
    private $db_name = "games_for_sale";
    private $username = "root";
    private $password = "";
    public $conn;

    // get the database connection
    public function getConnection(){

        $this->conn = null;

        try{
            $this->conn = new PDO("mysql:host=" . $this->host . ";dbname=" . $this->db_name, $this->username, $this->password);
        }catch(PDOException $exception){
            echo "Connection error: " . $exception->getMessage();
        }

        return $this->conn;
    }
}

用户等级：

class User{
    //database connection
    private $conn;
    private $table_name = "users";

    //object properties
    public $id;
    public $firstname;
    public $lastname;
    public $email;
    public $contact_number;
    public $address;
    public $password;
    public $access_level;
    public $access_code;
    public $status;
    public $created;
    public $modified;

    //constructor
    public function _construct($db){
        $this->conn = $db;
    }

    //check if given email exist in the database
    function emailExists()
    {

        $query = "SELECT id, firstname, lastname, access_level, password, status from " . $this->table_name . " where email = ?";

        //prepare this query
        $stmt = $this->conn->prepare($query);

        //sanitize
        $this->email = htmlspecialchars(strip_tags($this->email));

        //bind given email value
        $stmt->bindParam(1, $this->email);

        //execute the query
        $stmt->execute();

        //get number of rows
        $num = $stmt->rowCount();

        //if email exists, assign values to object properties for easy access and use for php sessions
        if ($num > 0) {

            //get record details / values
            $row = $stmt->fetch(PDO::FETCH_ASSOC);

            //assign values to object properties
            $this->id = $row['id'];
            $this->firstname = $row['firstname'];
            $this->lastname = $row['lastname'];
            $this->access_level = $row['access_level'];
            $this->password = $row['password'];
            $this->status = $row['status'];

            //return true because email exists in the database
            return true;
        }

        //retturn false if email does not exist in the database
        return false;
    }

}

我得到的错误：

致命错误：未捕获错误：在 user.php:34 中调用成员函数 prepare() 堆栈跟踪：
#0 login.php(34): User->emailExists()
#1 {main} 在 user.php 中抛出在第 34 行

标签： phpsql