Untitled

How to update but if field is empty not
if ($this->data['file'] == "") {
    unset($this->data['file']);
}

$update['description'] = $_POST['description']; //just another field
if($_POST['file']['name'] == "") //check if there's a new file
  $update['filename'] = $this->book->file_name; //current file name
else
  $update['filename'] = $_POST['file']['name']; //new file name in case the user uploaded a new file

$this->book->update($update); //update no matter what