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CodeIgniter 101 Tutorial


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A tutorial about CodeIgniter. It's purpose is to help someone with no prior knowledge of frameworks, to understand it's basic principles and how it works.

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CodeIgniter 101 Tutorial

  1. 1. Basic Tutorial
  2. 2. Index This is a tutorial with basic instructions about CodeIgniter.  It’s purpose is to help someone with no prior knowledge of frameworks, to understand it’s basic principles and how it works.      Index About Frameworks About MVC Intro to CodeIgniter Controllers Routes File Models
  3. 3. Frameworks Frameworks are abstract, reusable platforms where we can develop our applications. They help in writing reusable and better constructed code. Their main characteristic is the MVC (Model – View – Control) architecture pattern.
  4. 4. MVC The MVC architecture pattern separates the representation of data from the logic of the application. The View is what the visitors of the web application see. The Controller is responsible for handling the incoming requests, validating input and showing the right view. The Model is responsible for accessing the database or executing other operations.
  5. 5. MVC Controller Gets incoming requests. Displays the right View. Communicates with the model. The Controller calls the Model. Points to a View and carries data. Triggers a Controller The Model retrieves / creates the data asked and returns them to the Controller Model Queries the database. Executes operations. Gives data to controller. View What the visitors see. Html pages with PHP. Displays data from Controller
  6. 6. What is CodeIgniter CodeIgniter is a PHP framework, easy to learn, suitable for beginners.  It needs no extra configuration.  You do not need to use the command line.  It is extremely light.  You don’t need to learn a templating language.  It is suitable for small or big projects. All in all, you just need to know some PHP to develop the applications you want.
  7. 7. Intro to CodeIgniter How does a Controller trigger? Each Controller triggers by a certain URI. What happens when a Controller is triggered? It then calls a Model (if any data should be retrieved or created), it finds the View that should be shown to the visitor and then it returns that View with the corresponding data. How does CI knows what Controller to trigger? This is defined by routes. Routes is a PHP configuration file that maps each URL of our web project to a Controller and a certain function.
  8. 8. Intro to CodeIgniter User enters the URI of the project CI gets the request and checks the routes file to find any matches. If a match is found, it triggers the right Controller and function. View and data is represented to the user. After the data is retrieved the Controller finds the right View and returns it. The Controller calls the right Model to retrieve / create the data needed.
  9. 9. Controllers – The Class A controller in CI is basically a custom made class, which inherits from the CI_Controller class. class WELCOME extends CI_Controller { } Create a controller with name “welcome.php”. The new controller is located into applications/controllers folder. In every controller we create, the constructor method must be declared. In the constructor we can load libraries, models, the database, create session variables and generally define content that will be used by all methods. The constructor must have the same name as the class.
  10. 10. Controllers – The Constructor public function WELCOME() { parent::_construct(); The first function of the controller is the constructor, where we can load… $this->load->helper(‘url’); $this->load->helper(‘file’); … the helper libraries we may need…. $this->load->database(); … the database of our project… $this->load->model(‘welcome_model’); } … and the models we need.
  11. 11. Controllers – The Functions Then we can write the functions of the controller, that will be triggered by the system. The functions can either perform some operations (through the model), load a view, or even both. public function home () { if (!file_exists(application/views/home.php)){ show_404(); } $this->load->view(‘home’); } The most usual operation is to check if a view file exists and load it. View files are located in application/views folder. Views are what the visitors see. In case it does not exist, a 404 error message is displayed to the visitor.
  12. 12. Controllers – The Functions public function home () { if (!file_exists(application/views/home.php)){ show_404(); } $data[‘files’]=$this->welcome_model->get_data(); $this->load->view(‘home’,$data); } In case we need to send some data to the view, we retrieve them by calling the right function from the model and then load them with the view. In the above example, the data is then accessible by the name “files” in the “home” view.
  13. 13. Routes File The routes file contains the matches for the URIs and the Controllers / Functions. There is a default controller which is triggered from the Base URL of our project (e.g. $route[„default_controller‟]=“controller_name/function_name”; So, if we try to access the, the routes file understands it as the default controller and triggers the controller and function we define, e.g. the welcome controller and the home function. $route[„default_controller‟]=“welcome/home”;
  14. 14. Routes File There is a pattern which we have to follow in order to create mappings of URIs and controllers / functions. The first segment is reserved for the controller class, the second for the function and the third of any values we want to pass as arguments (optional). In case we don’t want to follow this pattern, the URI handler has to be reconfigured. If we want to map another URI, we have to follow that pattern. In the following example if the URI is, CI triggers the welcome controller and the blog method. $route[„welcome/blog‟]=“welcome/blog”;
  15. 15. Models – Class/ Constructor In a model we perform some tasks such as execute database queries, read / write files or perform other operations. The models are located in applications/models folder. class Welcome_model extends CI_Model { Each model we create, extends from the CI_Model. public function _construct () { $this->load->database(); } At first we have to write the constructor of the model. In the constructor we load the database or other helper libraries. }
  16. 16. Models - Functions class Welcome_model extends CI_Model { public function get_data() { $query=$this->db->get(….); /* perform other operations */ return $files; } } In a model function we can perform any operation we need, and then return the data to the corresponding function in the controller.
  17. 17. End of tutorial The previous topics complete a basic intro into CodeIgniter and how it essentially works. CodeIgniter supports helpers, which is essentially a collection of functions in a category, for example the helper for working with files (read / write) is “file” and libraries as form validation. All of these can come in handy and help a lot in developing your projects. The database class of CodeIgniter supports both traditional structures as Active Records patterns. Also, someone could set up CodeIgniter to run with Doctrine (ORM), a topic that will be presented in another tutorial. For the complete CodeIgniter documentation visit here. Thank you for reading my tutorial.