为什么我在 PHP 中收到“试图获取非对象的属性”错误？

Question

I'm working on a form where you can update a student's information in the database.

I've been getting this error:

Notice: Trying to get property of non-object in [...]/EditPersonalInfo.php on line 54.

I know this is a common error asked about on here but none of the solutions I found so far have fixed the issue in my case.

Here is my code:

// At the top of the page I also made sure to require_once my server.php file, so the database does connect

<?php 
        if (isset($_POST['update_personal'])) {

            $phone = trim($_POST['phoneNumber']);       
            $address = trim($_POST['address']); 
            $id = $_SESSION['id'];

            // The three variables above work when echoed.

            $query = "UPDATE StudentInfo SET PhoneNumber = $phone , Address = '$address' WHERE Student_ID = $id";

            // The above looks fine when echoed

            // The problem starts here
            $result = $conn->query($query);

            // Line 54
            if($result->num_rows == 1) {        

               // This was an attempt to set session variables when things didn't work. Nothing
               // in the database has changed though.
               while ($row = $result->fetch_assoc()){
                    $_SESSION['address'] = $row['Address'];
                    $_SESSION['phone'] = $row['PhoneNumber'];
                    }
            }

        }
    ?>

This same approached worked earlier when I was setting session variables:

// When user submits login info.
    if (isset($_POST['login_user']))
    {
        // Get info from forms and trim white space, then save as variables.
        $username = trim($_POST['username']);
        $password = trim($_POST['password']);

        // If no errors.
        if (count($errors) == 0) {

            // Select user info from server. 
            $query = "SELECT * FROM StudentInfo WHERE Username='$username' AND Password='$password'";

            $result = $conn->query($query);

            if($result->num_rows == 1) 
            {
            // Load user from server, send to home page

                while ($row = $result->fetch_assoc()){
                    $_SESSION['id'] = $row['Student_ID'];
                    $_SESSION['fname'] = $row['FirstName'];
                    $_SESSION['lname'] = $row['LastName'];
                    $_SESSION['dob'] = $row['DateOfBirth'];
                    $_SESSION['address'] = $row['Address'];
                    $_SESSION['email'] = $row['EmailAddress'];
                    $_SESSION['due'] = $row['AmountDue'];
                    $_SESSION['phone'] = $row['PhoneNumber'];
                    $_SESSION['emergency'] = $row['EmergencyContact_ID'];
                    $_SESSION['coursesid'] = $row['CourseList_ID'];
                    $_SESSION['res'] = $row['Residency_ID'];
                    $_SESSION['user'] = $row['Username'];
                    $_SESSION['pass'] = $row['Password'];

                }

            header('location: home/home.php');
            }
        }
    }

Any help would be much appreciated.

Answer 1

the problem is with $result->num_rows use rowCount

so correct code will be

    if($result->rowCount() == 1)