试图获取非对象的属性 - PHP

因此，我试图获取与teacher_id用户输入的老师的名字和姓氏相对应的 ，但是当我尝试获取teacher_id它时，它会输出Trying to get property of non-object. 有没有人有任何想法？

PHP

<?php

// PROCESSES STUDENT INFO

// get connect page
require '../../connect.php';

// get input info
$student_id = $_POST['student_id'];
$first_name = $_POST['first_name'];
$last_name = $_POST['last_name'];
$teacher_first_name = $_POST['teacher_first_name'];
$teacher_last_name = $_POST['teacher_last_name'];

// check if input is not empy
if(!empty($student_id) && !empty($first_name) && !empty($last_name) && !empty($teacher_first_name) && !empty($teacher_last_name)) {

    // check if numeric inputs have a number
    if(is_numeric($student_id)) {
        $teacher_check = mysqli_query($link, "SELECT teacher_id FROM teachers WHERE first_name='$teacher_first_name' AND last_name='$teacher_last_name'");

        // check if teacher exists
        if($teacher_check) {
            $row = $teacher_check->fetch_object();

            $result = mysqli_query($link, "INSERT INTO students (student_id, first_name, last_name, teacher_id) VALUES ($student_id, '$first_name','$last_name', $row->teacher_id)");

            if($result) {
                header("Location: ../../../admin.php?message=Success!");
            } else {
                echo mysqli_error($link);
                // header("Location: ../../../admin.php?message=Sorry we ran into an error");
            }
        } else {
            header("Location: ../../../admin.php?message=Teacher Does Not Exist");
        }
    } else {
        header("Location: ../../../admin.php?message=Please add a number for Student ID");
    }

} else if (empty($student_id) || empty($first_name) || empty($last_name)) {
    header("Location: ../../../admin.php?message=Please add you're input values");
}

?>