CONTOH UPDATE DATA - DROPDOWN FORM
Note : Perhatikan "subktgr"

(A) AJAX - INDEX

<div class="form-group">
	<label class="control-label col-md-3 col-sm-3 col-xs-12">Sub Kategori</label>
    	<div class="col-md-9 col-sm-9 col-xs-12" id="subktgr_id">
        <?php
	        echo form_dropdown("subktgr",$subktgr,"",'id="id_subktgr" class="form-control"');
        ?>
        </div>
</div>

function edit(id)
{
	$('#form')[0].reset();
		$.ajax({
	    	url : "<?php echo site_url('ktgr_brng/ajax_edit/')?>/" + id,
	    	type: "GET",
	    	dataType: "JSON",
	    	success: function(data)
	    	{
	    		method = 'ubah';
				url = '<?php echo site_url('ktgr_brng/proses_edit')?>';
	        	$('[name="id_ktgr_brng"]').val(data.id_ktgr_brng);
	        	$('[name="ktgr_brng"]').val(data.ktgr_brng).attr("readonly","readonly");
	        	$('[name="subktgr"]').val(data.sub).change();
	        	$('[name="keterangan"]').text(data.keterangan);
				$('#form-modal').modal('show');
	        	$('.modal-title').text('Form Edit Data');
	        },
	    	error: function (jqXHR, textStatus, errorThrown)
	    	{
	        	alert('Error get data from ajax');
	    	}
		});
}

(B) LOGIC

function ajax_edit($id)
{
	$data = $this->m_all->get_by_id($this->table, $this->primary, $id);
	echo json_encode($data);
}

function get_by_id($table, $id_table, $id)
{
	$this->db->select('*');
    $this->db->from($table);
    $this->db->where($id_table, $id);
    $q = $this->db->get();
    return $q->row();
}