CodeIgniter Interview Questions

CodeIgniter is a powerful MVC based PHP framework with a very small footprint, built for developers who need a simple and elegant toolkit to create full-featured web applications.

As on Sept 19, 2019 CodeIgniter 3.1.11 is the latest version of the framework. You can download it from here

In system/core/CodeIgniter.php, check CI_VERSION constant value define(‘CI_VERSION’, ‘3.0.6’);

Following Databases supported are supported by Codeigniter Frameworks

• MySQL (5.1+) via the MySQL (deprecated), MYSQLI and PDO drivers
• Oracle via the oci8 and PDO drivers
• PostgreSQL via the Postgre and PDO drivers
• MS SQL via the MsSQL, Sqlsrv (version 2005 and above only) and PDO drivers
• SQLite via the SQLite (version 2), sqlite3 (version 3) and PDO drivers
• CUBRID via the Cubridand PDO drivers
• Interbase/Firebird via the iBase and PDO drivers
• ODBC via the ODBC and PDO drivers (you should know that ODBC is actually an abstraction layer)

• Framework with a small footprint
• Simple solutions over complexity
• Clear documentation
• Exceptional performance
• Strong Security
• Nearly zero configuration

As the name suggests, helpers help you with tasks.Each helper file is simply a collection of functions in a particular category.They are simple, procedural functions.Each helper function performs one specific task, with no dependence on other functions.

CodeIgniter does not load Helper Files by default, so the first step in using a Helper is to load it. Once loaded, it becomes globally available in your controller and views.

Helpers are typically stored in your system/helpers, or application/helpers directory

Loading a helper file is quite simple using the following method:

$this->load->helper('name');

Where name is the file name of the helper, without the .php file extension or the “helper” part.
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In Software engineering routing is the process of taking a URI endpoint (that part of the URI which comes after the base URL) and decomposing it into parameters to determine which module, controller, and action of that controller should receive the request.In Codeigniter typically there is a one-to-one relationship between a URL string and its corresponding controller class/method.The segments in a URI normally follow this pattern:example.com/class/function/id/.In CodeIgniter, all routing rules are defined in your application/config/routes.php file.

CodeIgniter’s Hooks feature provides a way to modify the inner workings or functionality of the framework without hacking the core files.

The following is a list of available hook points.

• pre_system Called very early during system execution.
• pre_controller Called immediately prior to any of your controllers being called.
• post_controller_constructor Called immediately after your controller is instantiated, but prior to any method calls happening.
• post_controller Called immediately after your controller is fully executed.
• display_override Overrides the _display() method.
• cache_override Enables you to call your own method instead of the _display_cache() method in the Output Library. This permits you to use your own cache display mechanism.
• post_system Called after the final rendered page is sent to the browser, at the end of system execution after the finalized data is sent to the browser.

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CodeIgniter uses a few functions for its operation that are globally defined, and are available to you at any point. These do not require loading any libraries or helpers.

• is_php($version)
• is_really_writable($file)
• config_item($key)
• set_status_header($code[, $text = ”])
• remove_invisible_characters($str[, $url_encoded = TRUE])
• html_escape($var)
• get_mimes()
• is_https()
• is_cli()

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To set default timezone in Codeigniter open application/config.php file and add below code in it.

date_default_timezone_set('your timezone');

In Codeigniter, you can link images/CSS/JavaScript by using the absolute path to your resources.

Something like below

// References your $config['base_url']
<img src="<?php echo site_url('images/myimage.jpg'); ?>" />

An inhibitor is an error handling class in Codeigniter. It uses PHP ‘s native functions like register_shutdown_function , set_exception_handler, set_error_handler to handle parse errors, exceptions, and fatal errors.

Follow below steps to index.php from URL in Codeigniter

• Step 1: Open config.php and replaces

  $config['index_page'] = "index.php" to $config['index_page'] = "" 
  and 
  $config['uri_protocol'] ="AUTO" to $config['uri_protocol'] = "REQUEST_URI"
  

• Step 2: Change your .htaccess file to

  RewriteEngine on
  RewriteCond $1 !^(index\.php|[Javascript / CSS / Image root Folder name(s)]|robots\.txt)
  RewriteRule ^(.*)$ /index.php/$1 [L]

In Codeigniter, models will typically be loaded and called from within your controller methods. To load a model you will use the following method:

$this->load->model('model_name');

If your model is located in a sub-directory, include the relative path from your model’s directory. For example, if you have a model located at application/models/blog/Posts.php you’ll load it using:

$this->load->model('blog/Posts');

Once your Model loaded, you will access its methods using an object with the same name as your controller:

Example

class Blog_controller extends CI_Controller {
        public function blog()
        {
                $this->load->model('blog');

                $data['query'] = $this->blog->get_last_ten_entries();

                $this->load->view('blog', $data);
        }
}

Sessions in CodeIgniter

In CodeIgniter Session class allows you maintain a user’s “state” and track their activity while they are browsing your website.
In order to use session, you need to load Session class in your controller.

$this->load->library(‘session’); method is used to sessions in CodeIgniter

$this->load->library('session');

Once loaded, the Sessions library object will be available using:

$this->session

Reading session data in CodeIgniter

Use $this->session->userdata(); method of session class to read session data in CodeIgniter.

Usage

$this->session->userdata('your_key');

You can also read a session data by using the magic getter of CodeIgniter Session Class

Usage

$this->session->item

Where an item is the name of the key you want to retrieve.

Creating a session in CodeIgniter

Session’s Class set_userdata() method is used to create a session in CodeIgniter. This method takes an associative array containing your data that you want to add in session.

Example

$newdata = array(
        'username'  => 'johndoe',
        'email'     => 'johndoe@some-site.com',
        'logged_in' => TRUE
);
$this->session->set_userdata($newdata);

If you want to add userdata one value at a time, set_userdata() also supports this syntax:

$this->session->set_userdata('some_name', 'some_value');

Removing Session Data

Session’s Class unset_userdata() method is used to remove a session data in CodeIgniter. Below are example usages of same.

Unset particular key

$this->session->unset_userdata('some_key');

Unset an array of item keys

 $array_items = array('username', 'email');
 $this->session->unset_userdata($array_items);

Read More https://www.codeigniter.com/userguide3/libraries/sessions.html

CodeIgniter DB Class insert_id() method is used to get last insert id.

Usage:

function add_post($post_data){
   $this->db->insert('posts', $post_data);
   $insert_id = $this->db->insert_id();
   return  $insert_id;
}

$this->load->library(‘library_name’); method is used to load a library in CodeIgniter.

Usage:
//Loading Cart library

$this->load->library('cart');

Using Cart library methods

$data = array(
        'id'      => 'sku_9788C',
        'qty'     => 1,
        'price'   => 35.95,
        'name'    => 'T-Shirt',
        'options' => array('Size' => 'L', 'Color' => 'Red')
);

$this->cart->insert($data);

CLI is a text-based command-line interface for interacting with computers via a set of commands.

In Codeigniter, we can use CLI for

• Run your cronjobs without needing to use wget or curl
• Make your cron-jobs inaccessible from being loaded in the URL by checking the return value of is_cli().
• Make interactive “tasks” that can do things like set permissions, prune cache folders, run backups, etc.
• Helps to integrate Codeigniter with other applications in other languages. For example, a random C++ script could call one command and run code in your models!

We can use redirect helper to do 301 redirects in Codeigniter.

Syntax :

 redirect($uri = '', $method = 'auto', $code = NULL)

Parameter:

    $uri (string) – URI string
    $method (string) – Redirect method (‘auto’, ‘location’ or ‘refresh’)
    $code (string) – HTTP Response code (usually 302 or 303)

Return type: void

Sample Usage:-

redirect('/posts/13', 'New location', 301); 

Code for Checking a field or column exists or not in a Codeigniter table.

if ($this->db->field_exists('field_name', 'table_name'))
{
        // some code...
}

In Codeigniter is_cli() method is used to check request is from the command line or not.
Returns TRUE if the application is run through the command line and FALSE if not.

Below images give you an understanding of how data flows throughout the system in Codeigniter.

1. The index.php serves as the front controller, initializing the base
   resources needed to run CodeIgniter.
2. The Router examines the HTTP request to determine what should be done
   with it.
3. If a cache file exists, it is sent directly to the browser, bypassing
   the normal system execution.
4. Security. Before the application controller is loaded, the HTTP
   request and any user submitted data are filtered for security.
5. The Controller loads the model, core libraries, helpers, and any
   other resources needed to process the specific request.
6. The finalized View is rendered then sent to the web browser to be
   seen. If caching is enabled, the view is cached first so that on
   subsequent requests it can be served.

Source: https://www.codeigniter.com/user_guide/overview/appflow.html

// Setting a config variable dynamically
$this->config->set_item('variable_name', value);
// Getting value of config variable in Codeigniter.
$this->config->item('variable_name');

//DELETE FROM table WHERE id = $id
$conditions =['id' => $id]
$this->db->delete('table_name', $conditions); 

// Deleting records from more than one tables in one go
$id=1;
$tables = array('table1', 'table2', 'table3');
$this->db->where('id', $id);
$this->db->delete($tables);

You can implement form validations in Codeigniter using a form_validation library. Below is simple server-side validation in Codeigniter.

In your Controller

         $this->load->helper(array('form'));			
         /* Load form validation library */ 
         $this->load->library('form_validation');			
         /* Set validation rule for name field in the form */ 
         $this->form_validation->set_rules('firstname', 'FirstName', 'required'); 
			
         if ($this->form_validation->run() == FALSE) { 
              $this->load->view('myform'); 
         } 
         else { 
            $this->load->view('formsuccess'); 
         } 

In your View

 <?php echo validation_errors(); ?> 

abc.com/user/edit/ramesh

The default URL pattern in CodeIgniter consists of 4 main components. They are :

1. A server name (abc.com)
2. A Controller (user)
3. An Action or method (edit)
4. An optional action parameter (ramesh)

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// Getting random rows from database in CodeIgniter
$this->db->select('*');
$this->db->from('table_name');
$this->db->order_by("column_name", "random");
$result = $this->db->get()->result(); 

Codeigniter Is Called a loosely based MVC framework, this is because unlike others the controllers’ classes such as models and views are not mandatory in CodeIgniter. Moreover, one can modify CodeIgniter to utilize HMVC as well.

• DataMapper
• Doctrine
• Gas ORM

• Classes found in the libraries/ directory
• Helper files found in the helpers/ directory
• Custom config files found in the config/ directory
• Language files found in the system/language/ directory
• Models found in the models/ folder

To autoload resources, open the application/config/autoload.php file and add the item you want loading to the autoload array. You’ll find instructions in that file corresponding to each type of item.

All Routing rules in Codeigniter are defined in your application/config/routes.php file.

By default, all logs in Codeigniter are stored in logs/ directory. To enable error logging you must set the “threshold” for logging in application/config/config.php. Also, your logs/ must be writable.

$config['log_threshold'] = 1;

There are three message types in Codeigniter. They are :

• Error Messages. These are actual errors, such as PHP errors or user errors.
• Debug Messages. These are messages that assist in debugging. For example, if a class has been initialized, you could log this as debugging info.
• Informational Messages. These are the lowest priority messages, simply giving information regarding some process.

Csrf is used to set the protection in CodeIgniter. To set csrf, you have to put the corresponding config value True.

Syntax: $config['csrf_protection'] = TRUE;