PHP 致命错误 调用未定义的方法

我一直在寻找解决问题的方法，但每种情况似乎都与我的不同。我正在尝试使用 PHP 导入 CSV 文件。

这是我收到的错误：

致命错误：在第 66 行的 C：''wamp''www''Projet''models''Db.class.php 中调用未定义的方法 Teacher：：email_teacher（）

这是来自索引.php。提前感谢您的帮助。

<?php
session_start();
define('VIEW_PATH','views/');
define('CONT_PATH','controllers/');
$csvfileTeacher = 'models/professeurs.csv';

function uploadClass($classe) {
        require 'models/' . $classe . '.class.php';
    }
    spl_autoload_register('uploadClass');

function getTeacher($csvfileTeacher) {
    $teachers = array ();
    if (file_exists ( $csvfileTeacher )) {
        $fcontents = file ( $csvfileTeacher );
        $i = count ( $fcontents ) - 1;
        for($index = 1; $index <= $i; $index ++) {
            $icontent = $fcontents [$index];
            preg_match ( '/^(.*);(.*);(.*);(.*)/', $icontent, $result );
            $teachers [$index] = new teacher ( $result [1], $result [2], $result [3], $result [4] );
        }
    }
    return $teachers;
}
if (file_exists ( $csvfileTeacher )) {
    $teachers = getTeacher ( $csvfileTeacher );
    foreach ( $teachers as $teacher ) {
        Db::getInstance ()->insert_teacher ( $teacher );  ///here is where the problem seems to be 
    }
}   

下面是来自 Db.class.php 的函数 insert_teacher（）：

public function insert_teacher($teacher) {
    $query = 'INSERT INTO teachers VALUES ( ' . $this->_db->quote ( $teacher->email_teacher () ) . ',' . $this->_db->quote ( $teacher->firstname_teacher () ) . ',' . $this->_db->quote ( $teacher->lastname_teacher () ) . ',' . $this->_db->quote ( $teacher->supervisor () ) .')';          
    $this->_db->prepare ( $query )->execute ();
}

这是教师课：

<?php
    class Teacher{
        private $_email_teacher;
        private $_firstname_teacher;
        private $_lastname_teacher;
        private $_supervisor;
        public function  __construct($email_teacher,$firstname_teacher,$lastname_teacher,$supervisor){
            $this->_email_teacher=$email_teacher;
            $this->_firstname_teacher=$firstname_teacher;
            $this->_lastname_teacher=$lastname_teacher;
            $this->_supervisor=$supervisor;
        }
        public function email(){
            return $this->_email_teacher;
        }
        public function firstname(){
            return $this->_firstname_teacher;
        }
        public function lastname(){
            return $this->_lastname_teacher;
        }
        public function supervisor(){
            return $this->_supervisor;
        }
    }
?>