//model
public function importmhs($data) {
    $this->db->insert_batch('mahasiswa', $data);
}

public function validasinim() {
    $this->db->select('nim_mhs');
    $this->db->where('nim_mhs');
    $query = $this->db->get('mahasiswa');
    $num = $query->num_rows();
    return $num;
}

//controller
$data_upload = $this->upload->data();
$excelreader = new PHPExcel_Reader_Excel2007();
$loadexcel   = $excelreader->load('upload/'.$data_upload['file_name']);
$sheet       = $loadexcel->getActiveSheet()->toArray(null, true, true ,true);

$data = array();

$numrow = 1;
foreach($sheet as $row){
    if($numrow > 1){
        array_push($data, array(
            'nim_mhs'           => $row['A'],
            'nama_mhs'          => $row['B'],
            'nohp_mhs'          => $row['C'],
            'email_mhs'         => $row['D'],
            'set_lulus'         => $row['E'],
            'flag_bagidosbing'  => $row['F'],
        ));
    }
    $numrow++;
}

if ($row['A'] == "" OR $row['B'] == "" OR $row['C'] == "" OR $row['D'] == "") {
    $this->session->set_flashdata('error','Data masih ada yang kosong, silahkan cek kembali file excelnya ..');
    redirect('koordinator/mahasiswa');
} else {
    $ceknim = $this->m_mahasiswa->validasinim($row['A']);
    if ($ceknim > 0) {
        $this->session->set_flashdata('error','Data ada yang sama, silahkan cek kembali file excelnya ..');
        redirect('koordinator/mahasiswa');
    } else {
        $this->m_mahasiswa->importmhs($data);
        unlink(realpath('upload/'.$data_upload['file_name']));
        $this->session->set_flashdata('notif','Import File Berhasil ..');
        redirect('koordinator/mahasiswa');
    }
}