mysql real escape string error ketika saya mau login

Fatal error: Uncaught Error: Call to undefined function mysql_real_escape_string() in D:\XAMPP\xampp\htdocs\alfalah\sim\action\LoginAction.php:9 Stack trace: #0 D:\XAMPP\xampp\htdocs\alfalah\sim\action\LoginAction.php(54): getLogin('asep', '1234') #1 {main} thrown in D:\XAMPP\xampp\htdocs\alfalah\sim\action\LoginAction.php on line 9

<?php
session_start();
include_once '../db/DBConnection.php';
include_once '../model/Personal.php';
include_once '../model/User.php';
include_once '../library/Enkripsi.php';
$error=0;
function getLogin($username,$password){
    $user= mysql_real_escape_string($username,DBConnection::getConnection());//strip_tags($username); //untuk mencegah sql injektion
    $pwd= mysql_real_escape_string($password,DBConnection::getConnection());//strip_tags($password); //untuk encegah sql injektion
    $user=NULL;
    $sql="select * from user where username='$usr' and password='".encrypt_decrypt('encrypt', $pwd)."'";
    $dataQry  =  mysql_query($sql, DBConnection::getConnection())or die("Query error :".  mysql_error());
    while ($dataRow=  mysql_fetch_array($dataQry)){
      $user=new User();
      $user->setUserId($dataRow['id_user']);
      $user->setUsername($dataRow['username']);
      $user->setPassword($dataRow['password']);
      $user->setLevel($dataRow['level']);
      $user->setPersonalId($dataRow['personal_id']);
      $user->setPertanyaan($dataRow['pertanyaan']);
      $user->setJawaban($dataRow['jawaban']);
      $user->setPersonal(getPersonal($dataRow['personal_id']));
    }
    return $user;
}

function getPersonal($id){
    $personal=NULL;
    $sql="select * from personal where id_siswa='$id'";
    $dataQry  =  mysql_query($sql, DBConnection::getConnection())or die("Query error :".  mysql_error());
    while ($dataRow=  mysql_fetch_array($dataQry)){
      $personal=new Personal();
      $personal->setIdPersonal($dataRow['id_siswa']);
      $personal->setNamaAwal($dataRow['nama_awal']);
      $personal->setNamaTengah($dataRow['nama_tengah']);
      $personal->setNamaAkhir($dataRow['nama_akhir']);
      $personal->setTempatLahir($dataRow['tempat_lahir']);
      $personal->setTglLahir($dataRow['tgl_lahir']);
      $personal->setTelepon($dataRow['telepon']);
      $personal->setAlamat($dataRow['alamat']);
      $personal->setKota($dataRow['kota']);
      $personal->setPropinsi($dataRow['propinsi']);
      $personal->setNegara($dataRow['negara']);
      $personal->setEmail($dataRow['email']);
      $personal->setKelamin($dataRow['kelamin']);
      $personal->setKategoriSantri($dataRow['kategori_santri']);
      $personal->setTglGabung($dataRow['tgl_gabung']);
      $personal->setFoto($dataRow['foto']);
    }
    return $personal;
}
if($_POST){
    $loginPersonal =getLogin($_POST['txtUser'], $_POST['txtPassword']);
    if($loginPersonal==NULL){
        echo "<meta http-equiv='refresh' content='0; url=../'>";
        $error=1;
    }else{
        /* @var $_SESSION type */
        $_SESSION['SES_LOGIN'] = $loginPersonal->getPersonalId();
        $_SESSION['SES_USER'] = $loginPersonal->getUsername();
        $_SESSION['SES_NAMA']= $loginPersonal->getPersonal()->getNamaAwal()." ".$loginPersonal->getPersonal()->getNamaTengah()." ".$loginPersonal->getPersonal()->getNamaAkhir();
        $_SESSION['SES_PERSONALID']=$loginPersonal->getPersonalId();
        echo "<meta http-equiv='refresh' content='0; url=../index.php'>";

    }
}
?>
<script>
    var pesan=<?php echo $error; ?>;
    if(pesan===1){
        alert("Login Gagal Username Atau Password Tidak Valid !");
    }
</script>