Api.php

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

class Api extends REST_Controller {


 public function index()
 {
  $this->load->view('json');

 }

 public function login()
 {
  $this->form_validation->set_rules('username', 'username', 'required|max_length[256]');
  $this->form_validation->set_rules('password','password', 'required|min_length[2]|max_length[256]');
  return Validation::validate($this, '', '', function($token, $output)
  {
   $username = $this->input->post('username');
   $password = $this->input->post('password');
   $id = $this->M_api->login($username, $password);
   if ($id != false) {
    $token = array();
    $token['id'] = $id;
    $output['status'] = true;
    $output['username'] = $username;
    $output['token'] = JWT::encode($token, $this->config->item('jwt_key'));
   }
   else
   {
    $output['errors'] = '{"type": "invalid"}';
   }
   return $output;
  });
 }

 public function list_produk()
 {
  return Validation::validate($this, 'user', 'read', function($token, $output)
  {
   $list = $this->M_api->get_list_produk();
   foreach($list->result() as $data)
   {
    $output[] = array('id_produk' => $data->id_produk,
     'nama' => $data->nama,
     'harga' => $data->harga
     );
    $output['status'] = true;
   }
   return $output;
  });
 }

 public function detail_produk()
 {
  $this->form_validation->set_rules('id_produk', 'id_produk', 'required|max_length[256]');
  return Validation::validate($this, 'user', 'read', function($token, $output)
  {
   $detail = $this->M_api->detail_produk($this->input->post('id_produk'));
   foreach($detail->result() as $data)
   {
    $output = array('id_produk' => $data->id_produk,
     'nama' => $data->nama,
     'deskripsi' => $data->deskripsi,
     'harga' => $data->harga
     );
    $output['status'] = true;
   }
   return $output;
  });
 }

 public function transaksi()
 {
  $this->form_validation->set_rules('order', 'order', 'required');
  return Validation::validate($this, 'user', 'read', function($token, $output)
  {
   $parse = json_decode($this->input->post('order',true),true);
   $id_user = $parse[0]['id_user'];
   $lokasi = $parse[0]['lokasi'];
   $alamat = $parse[0]['alamat'];
   $detail = $parse[0]['myorder'];
   $total = $detail['total'];

 //insert tabel transaksi
   $insert_trans = array('tanggal' => date('Y-m-d'),
    'id_user' => $id_user,
    'total' => $total,
    'lokasi' => $lokasi,
    'alamat' => $alamat
    );

   $this->db->insert('transaksi',$insert_trans);
   $id_transaksi = $this->db->insert_id();

   foreach ($detail['detail'] as $data) {
    $nama[] = $data['nama'];
    $id_produk[] = $data['id_menu'];
    $qty[] = $data['qty'];
    $insert_det = array('id_transaksi' => $id_transaksi,
     'id_produk' => $data['id_menu'],
     'qty' => $data['qty'],
     );
    $this->db->insert('detail_transaksi',$insert_det);
   }
   $output['pesan'] = "berhasil";
   $output['status'] = true;
   return $output;
  });
 }


}

Lalu kita buat model dengan nama M_api.php

<?php
if (! defined('BASEPATH')) EXIT ('No direct script access allowed');

class M_api extends CI_Model {

public function login($username, $password)
 {
  $query = $this->db->query("SELECT * from user_agung where username ='$username' and status = 'active'");
  if ($query->num_rows() == 1)
  {
  foreach ($query->result() as $data) {
  $password_db = $data->password;
  if ($password_db == md5($password)) {
     return true;
    } else {
     return false;
    }

   }
  }
  else
  {
   return false;
    }
 }

 public function get_list_produk()
 {
  return $this->db->get('produk_agung');
 }

 public function detail_produk($id)
 {
  $query = $this->db->query("SELECT * from produk_agung where id_produk = '$id'");
  return $query;
    }
}