login.php，查询结果始终为false

Question

所以我得到同样的错误，这让我疯了。

  

布尔（假）

     

注意：尝试在第21行的/var/www/public/database.php＆gt;中获取非对象的属性

     

nicht eingeloggt

虽然选择正确，但似乎结果始终为false。我是PHP和数据库的新手，所以我还没有深入研究它。我希望有人能帮助我。

database.php

    <?php

    class dbanbindung {
        private $connection;

        function __construct(){
            $this->connection = new mysqli("localhost", "wt1p2_nutzer", "12345678", "wt1p2");
            if($this->connection->connect_error){
                echo die($this->connection->connect_error);
            }

        }

        public function login($mail, $pwd) {
            $result = $this->connection->query("SELECT pwd FROM user WHERE mail ='$mail'");
            var_dump($result);
            // line 20
            if ($result->num_rows == 1) {
                $zeile = $result->fetch_assoc();
                $pw_result = $zeile["pwd"];

                if (strcmp($pw_result, $pwd) == 0) {
                    return TRUE;
                } else {
                    return FALSE;
                }
            }

            function __destruct(){ 
            $this->connection->close();
        }
    }

    ?>

login.php

    <?php

    session_start();
    require ('database.php');
    $datenbank = new dbanbindung();

    $mail = $_POST["mail"];
    $pwd = hash('SHA512',$_POST["password"]);

    $login = $datenbank->login($mail,$pwd);

    if ($login) {
        echo ("login erfolgreich");

        $_SESSION["mail"] = $mail;
    }
    else {
        echo "nicht eingeloggt";
        // header("refresh:5;index.php#login");
    }

    ?>

index.php

    <form method="POST" action="login.php">
                    <table border="0" id="table">
                        <tr>
                            <th>Mailadresse:</th>
                            <th><input type="text" name="mail" value="" placeholder="example@example.com"></th>
                        </tr>
                        <tr>
                            <th>Passwort:</th>
                            <th><input type="password" name="password" value="" placeholder="******"></th>
                        </tr>
                    </table>
                    <br />
                    <input type="submit" value="Login">
                </form>