Building a simple API using Codeigniter 3

Codeigniter is a powerful PHP framework that is popular because it's fast, simple, and easy to configure. Version 4 is in the beta phase and version 3 is widely used for web development in all kinds of projects. So let's use it to create an API and serve single-page applications.

For this example, I will use

Apache 2

PHP 7.3

MariaDB 15.1

Simple Installation

1 - Download the framework at https://api.github.com/repos/bcit-ci/CodeIgniter/zipball/3.1.11, uncompress the file, rename the folder to 'baseapi' and put the folder in your server host folder, in my case '/var/www/html', now, access the URL http://localhost/basepapi, the default framework page should be shown.

Project Structure and connecting to a database

2 - If you ever had to deal with an MVC framework, the Codeigniter folder structure will seem pretty familiar.

application
- cache
- config
- controllers
- core
- helpers
- hooks
- language
- libraries
- logs
- models
- third_party
- views
system

We need to define two constants to expose our model and controllers folder.

Go to config/constants.php and add these two lines

define('MODELS_DIR', APPPATH . "models/");
define('CONTROLLERS_DIR', APPPATH . "controllers/");

Let's focus on the most used folders config, controllers, models, and views, and to start let's configure our database connection config/database.php.

Here we assume that you have a working MySQL database connection

$db['default'] = array(
    'dsn'   => '',
    'hostname' => 'localhost',
    'username' => 'root',
    'password' => 'root',
    'database' => 'baseapi',
    'dbdriver' => 'mysqli',
    'dbprefix' => '',
    'pconnect' => FALSE,
    'db_debug' => (ENVIRONMENT !== 'production'),
    'cache_on' => FALSE,
    'cachedir' => '',
    'char_set' => 'utf8',
    'dbcollat' => 'utf8_general_ci',
    'swap_pre' => '',
    'encrypt' => FALSE,
    'compress' => FALSE,
    'stricton' => FALSE,
    'failover' => array(),
    'save_queries' => TRUE
);

Now we refresh the page, if no connection errors were shown, we're fine to move on.

3 - Our Base Model

Let's create our BaseModel.php in the models folder.

<?php

abstract class BaseModel extends CI_Model
{
    abstract function get_table_name();

    public function persist($data)
    {
        $cleaned_data = $this->sanitize_fields($data, $this->get_table_name());

        if (isset($cleaned_data['id']) && intval($cleaned_data['id']) > 0)
            return $this->update($cleaned_data);

        unset($cleaned_data['id']);

        $this->db->set($cleaned_data);
        $this->db->insert($this->get_table_name());
        return $this->db->insert_id();
    }

    public function update($data)
    {
        $cleaned_data = $this->sanitize_fields($data, $this->get_table_name());
        $this->db->where('id', $cleaned_data['id']);
        return $this->db->update($this->get_table_name(), $cleaned_data);
    }

    public function sanitize_fields($data, $table_name)
    {
        $table_fields = $this->db->list_fields($table_name);
        $posted_fields = array_keys($data);
        foreach ($posted_fields as $posted_field) {
            if (!in_array($posted_field, $table_fields))
                unset($data[$posted_field]);
        }
        return $data;
    }

    function get_by_id($id)
    {
        $this->db->select('*');
        $this->db->from($this->get_table_name());
        $this->db->where('id', $id);
        $query = $this->db->get();
        return $query->result();
    }

    function get_all()
    {
        $this->db->select('*');
        $this->db->from($this->get_table_name());
        $query = $this->db->get();
        return $query->result();
    }
}

4 - Controllers

On the folder controllers, let's create a new file called BaseController.php

Codeigniter is primarily an MVC framework so we need to make some modifications to work as a service API.

Our controller needs to deal with getting, PUT, DELETE, and POST requests, we need to enable CORS by adding some lines to our constructor. We need also a function to get the input and convert to JSON, and a default behavior dealing with POST and DELETE REQUEST.

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

abstract class BaseController extends CI_Controller
{
    public function __construct()
    {
        parent::__construct();
        header('Access-Control-Allow-Origin: *');
        header("Access-Control-Allow-Headers: X-API-KEY, Origin, X-Requested-With, Content-Type, Accept, Access-Control-Request-Method");
        header("Access-Control-Allow-Methods: GET, POST, OPTIONS, PUT, DELETE");
        $method = $_SERVER['REQUEST_METHOD'];
        if ($method == "OPTIONS") {
            die();
        }

        $this->load->database();

        $this->persist_or_remove();
    }

    public function index(){
        echo 'Hello !';
    }

    public function get_data()
    {
        $json_str = file_get_contents('php://input');
        $data = json_decode($json_str);
        return $data;
    }

    public function persist_or_remove()
    {

        if ($this->is_delete()) {
            $this->remove();
        } elseif ($this->is_post()) {
            $this->persist();
        }
    }

    public function is_get()
    {
        return $_SERVER["REQUEST_METHOD"] === "GET";
    }

    public function is_post()
    {
        return $_SERVER["REQUEST_METHOD"] === "POST";
    }

    public function is_delete()
    {
        return $_SERVER["REQUEST_METHOD"] === "DELETE";
    }

    public function json_response($flag, $msg, $obj)
    {
        $res = (object) array(
            'flag' => $flag,
            'msg' => $msg,
            'obj' => $obj
        );

        return json_encode($res);
    }

    abstract protected function persist();
    abstract protected function remove();
}

The default Codeigniter controller is Welcome.php so when we access http://localhost/baseapi the controller that deals with the request is the default controller, we need to change it by going to config/routes.php and change this line

$route['default_controller'] = 'welcome';

$route['default_controller'] = 'BaseController';

Now, access http://localhost/baseapi, and if our "Hello !" (the index function) appears we are good to go.

For last, lets create a controller that inherits the BaseController:

<?php
require_once(CONTROLLERS_DIR . 'BaseController.php');

class Users extends BaseController
{
    public function __construct()
    {
        parent::__construct();
        $this->load->model('user');
    }

    public function index()
    {
        if (parent::is_get()) {
            $response = $this->user->get_all();
            echo parent::json_response(TRUE, "OK", $response);
        }
    }

    public function persist()
    {
        $this->user->persist(parent::get_data());
    }

    public function remove()
    {
        $this->user->remove(parent::get_data());
    }
}

Now we can get all users in the database by sending a GET request to http://localhost/baseapi/index.php/users, insert and update by sending POST or DELETE.

Here is the official documentation quote:

CodeIgniter is an Application Development Framework - a toolkit - for people who build web sites using PHP. Its goal is to enable you to develop projects much faster than you could if you were writing code from scratch, by providing a rich set of libraries for commonly needed tasks, as well as a simple interface and logical structure to access these libraries. CodeIgniter lets you creatively focus on your project by minimizing the amount of code needed for a given task.

Reference: https://codeigniter.com/user_guide/index.html

Building a simple API using Codeigniter 3

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