Fitur upload file di CodeIgniter 3

Karyawan.php

public function tambah()
{
    $this->load->helper('form');
    $this->load->library('form_validation');

    $this->form_validation->set_rules('userfile', 'Syarat', 'callback_validasi_file');

    if ($this->form_validation->run()) {
        $upload = $this->upload->data();
        $file_name = $upload['file_name'];

        $params = array(
            'syarat' => $file_name,
        );
        $this->karyawan_model->add_karyawan($params);

        $this->session->set_flashdata('success', '<div class="alert alert-success" role="alert">Data berhasil disimpan</div>');
        redirect('karyawan/tambah');
    } else {
        $this->load->view('karyawan/tambah');
    }
}

public function ubah($id_karyawan = '')
{
    $data['karyawan'] = $this->karyawan_model->get_karyawan($id_karyawan)->row();

    if (empty($data['karyawan'])) {
        show_404();
    } else {
        $this->load->helper('form');
        $this->load->library('form_validation');

        $userfile = isset($_FILES['userfile']['name']) ? $_FILES['userfile']['name'] : '';
        if (!empty($userfile)) {
            $this->form_validation->set_rules('userfile', 'Syarat', 'callback_validasi_file');
        }

        if ($this->form_validation->run()) {
            $karyawan = $data['karyawan'];
            $file_name = $karyawan->syarat;
            if (!empty($userfile)) {
                if (!empty($file_name)) {
                    unlink('./public/file/' . $file_name);
                }
                $upload = $this->upload->data();
                $file_name = $upload['file_name'];
            }

            $params = array(
                'syarat' => $file_name,
            );
            $this->karyawan_model->update_karyawan($id_karyawan, $params);

            $this->session->set_flashdata('success', '<div class="alert alert-success" role="alert">Data berhasil disimpan</div>');
            redirect('karyawan/ubah/' . $id_karyawan);
        } else {
            $this->load->view('karyawan/ubah', $data);
        }
    }
}

public function hapus($id_karyawan = '')
{
    $karyawan = $this->karyawan_model->get_karyawan($id_karyawan);

    if ($karyawan->num_rows() > 0) {
        $karyawan = $karyawan->row();
        if (!empty($karyawan->syarat)) {
            unlink('./public/file/' . $karyawan->syarat);
        }
        $this->karyawan_model->delete_karyawan($id_karyawan);
        redirect('karyawan');
    } else {
        show_404();
    }
}

public function validasi_file()
{
    $config['upload_path']          = './public/file/';
    $config['allowed_types']        = '*';
    $config['max_size']             = 2048;
    $config['overwrite'] = FALSE;

    $this->load->library('upload', $config);

    if ($this->upload->do_upload()) {
        return TRUE;
    } else {
        $this->form_validation->set_message('validasi_file', $this->upload->display_errors());
        return FALSE;
    }
}

Karyawan_model.php

class Karyawan_model extends CI_Model
{

    public function get_all_karyawan($sort = 'asc')
    {
        $this->db->order_by('id_karyawan', $sort);
        return $this->db->get('karyawan');
    }

    public function get_karyawan($id_karyawan)
    {
        $this->db->where('id_karyawan', $id_karyawan);
        return $this->db->get('karyawan');
    }

    public function add_karyawan($params)
    {
        $this->db->insert('karyawan', $params);
        return $this->db->insert_id();
    }

    public function update_karyawan($id_karyawan, $params)
    {
        $this->db->where('id_karyawan', $id_karyawan);
        return $this->db->update('karyawan', $params);
    }

    public function delete_karyawan($id_karyawan)
    {
        $this->db->where('id_karyawan', $id_karyawan);
        return $this->db->delete('karyawan');
    }
}

tambah.php

<?= form_open_multipart('karyawan/tambah', 'class="form-horizontal form-material"') ?>
<h4 class="card-title">Tambah Peserta Seleksi Manager</h4>
<?= $this->session->flashdata('success') ?>
<div class="row">
    <div class="col-6">
        <h4>Data Peserta Seleksi Manager</h4>
        <div class="form-group">
            <label class="col-md-12">Syarat</label>
            <div class="col-md-12">
                <input type="file" name="userfile" class="form-control">
                <small>Ukuran maksimal 2MB</small>
                <div class="text-danger"><?= form_error('userfile') ?></div>
            </div>
        </div>
    </div>
</div>
<div class="row">
    <div class="col-12">
        <div class="form-group">
            <div class="col-sm-12">
                <button type="submit" name="save" class="btn btn-success">Simpan</button>
                <?= anchor('karyawan', 'Kembali', 'class="btn btn-secondary"') ?>
            </div>
        </div>
    </div>
</div>
<?= form_close(); ?>

ubah.php

<?= form_open_multipart('karyawan/ubah/' . $karyawan->id_karyawan, 'class="form-horizontal form-material"') ?>
<h4 class="card-title">Ubah Peserta Seleksi Manager</h4>
<?= $this->session->flashdata('success') ?>
<div class="row">
    <div class="col-6">
        <h4>Data Peserta Seleksi Manager</h4>
        <div class="form-group">
            <label class="col-md-12">Syarat</label>
            <div class="col-md-12">
                <?php if (empty($karyawan->syarat)) : ?>
                    <p>Tidak ada file</p>
                <?php else : ?>
                    <?= anchor('public/file/' . $karyawan->syarat, 'Download', 'target=_blank'); ?>
                <?php endif; ?>
                <input type="file" name="userfile" class="form-control">
                <small>Ukuran maksimal 2MB</small>
                <small>*Kosongkan jika file tidak diubah</small>
                <div class="text-danger"><?= form_error('userfile') ?></div>
            </div>
        </div>
    </div>
</div>
<div class="row">
    <div class="col-12">
        <div class="form-group">
            <div class="col-sm-12">
                <button type="submit" name="save" class="btn btn-success">Simpan</button>
                <?= anchor('karyawan', 'Kembali', 'class="btn btn-secondary"') ?>
            </div>
        </div>
    </div>
</div>
<?= form_close(); ?>