Gk bisa edit form pake codeigniter

Gan permisi mau nnya kenapa yah saya gk bisa edit form didalam website sekolah buatan saya

Kodingan front end

<div class="col-sm-9 col-sm-offset-3 col-lg-10 col-lg-offset-2 main">
	<div class="row">
		<ol class="breadcrumb">
			<li><a href="#">
					<em class="fa fa-home"></em>
				</a></li>
			<li class="active">Edit Nilai</li>
		</ol>
	</div>
	<?php if ($this->session->flashdata('success')) : ?>
		<div class="alert alert-success" role="alert">
			<?php echo $this->session->flashdata('success'); ?>
		</div>
	<?php endif; ?>
	<div class="container-fluid">
		<div class="panel-button-tab-left">
			<form method="post"  action="<?php  echo base_url(). 'guru/nilai'?>">
				<button class="btn btn-primary" id="submit-buttons" type="submit" ​​​​​>List Nilai</button>
			</form>
		</div><br>
		<form action="<?php echo base_url("Guru/nilaiEdit/$nilai->id_nilai") ?>" method="post" enctype="multipart/form-data">
			<input type="hidden" name="id_nilai" value="<?php echo $nilai->id_nilai?>">
						<div class="col-md-8">
							<div class="form-group">
								<label for="id_siswa">Id Siswa :</label>
								<input type="text" class="form-control" name="nama_siswa" value="<?php echo $nilai->id_siswa ?>">
							</div>
						</div>
						<div class="col-md-8">
							<div class="form-group">
								<label for="id_kelas">Id Kelas :</label>
								<input type="text" class="form-control" name="id_kelas" value="<?php echo $nilai->id_kelas ?>">
							</div>
						</div>
						<div class="col-md-8">
							<div class="form-group">
								<label for="id_mapel">Id Mapel :</label>
								<input type="text" class="form-control" name="id_mapel" value="<?php echo $nilai->id_mapel ?>">
							</div>
						</div>
						<div class="col-md-8">
							<div class="form-group">
								<label for="id_mapel">uh_1 :</label>
								<input type="text" class="form-control" name="uh_1" value="<?php echo $nilai->uh_1 ?>">
							</div>
						</div>
						<div class="col-md-8">
							<div class="form-group">
								<label for="id_mapel">uh_2 :</label>
								<input type="text" class="form-control" name="uh_2" value="<?php echo $nilai->uh_2 ?>">
							</div>
						</div>


					<div class=col-md-12>
                		<button type="submit" class="btn btn-primary" value="simpan">Simpan</button>
                		<button type="reset" class="btn btn-danger">Reset</button>
               		</div>
         </form>
        </div>
  </div>

Kodingan back end

<?php defined('BASEPATH') or exit('No direct script access allowed');

class Model_nilai extends CI_Model
{
    private $_table = "nilai";
    public $id_nilai;
    public $id_guru;
    public $id_siswa;
    public $id_kelas;
    public $id_mapel;
    public $uh_1;
    public $uh_2;
    public $uh_3;
    public $uh_4;
    public $uh_5;
    public $uh_6;
    public $uh_7;
    public $uh_8;
    public $uts;
    public $uas;
    public $id_semester;

    public function rules()
    {
        return [
            [
            ]
        ];
    }

    public function getAll()
    {
        return $this->db->get($this->_table)->result();
    }

    public function getById($id_nilai)
    {
        return $this->db->get_where($this->_table, ["id_nilai" => $id_nilai])->row();
    }

    public function update()
    {
        $post = $this->input->post();
        // var_dump($post);
        $this->id_nilai = $post["id_nilai"];
        $this->id_guru = $post["id_guru"];
        $this->id_siswa =$post["id_siswa"];
        $this->id_kelas =$post["id_kelas"];
        $this->id_mapel =$post["id_mapel"];
        $this->uh_1 = $post["uh_1"];
        $this->uh_2 = $post["uh_2"];
        $this->uh_3 = $post["uh_3"];
        $this->uh_4 = $post["uh_4"];
        $this->uh_5 = $post["uh_5"];
        $this->uh_6 = $post["uh_6"];
        $this->uh_7 = $post["uh_7"];
        $this->uh_8 = $post["uh_8"];
        $this->uts = $post["uts"];
        $this->uas = $post["uas"];
        $this->id_semester =$post["id_semester"];

        $this->db->update($this->_table, $this, array("id_nilai" => $post["id_nilai"]));
    }

    public function delete($id_nilai)
    {
        return $this->db->delete($this->_table, array("id_nilai" => $id_nilai));
    }

    public function save()
    {
        $post = $this->input->post();
        // var_dump($post);
        // $this->id_nilai = $post["id_nilai"];
        $this->id_guru = $post["id_guru"];
        $this->id_siswa =$post["id_siswa"];
        $this->id_kelas =$post["id_kelas"];
        $this->id_mapel =$post["id_mapel"];
        $this->uh_1 = $post["uh_1"];
        $this->uh_2 = $post["uh_2"];
        $this->uh_3 = $post["uh_3"];
        $this->uh_4 = $post["uh_4"];
        $this->uh_5 = $post["uh_5"];
        $this->uh_6 = $post["uh_6"];
        $this->uh_7 = $post["uh_7"];
        $this->uh_8 = $post["uh_8"];
        $this->uts = $post["uts"];
        $this->uas = $post["uas"];
        $this->id_semester =$post["id_semester"];

        $this->db->insert($this->_table, $this);
    }


}