I am new to CI. Before I had worked extensively in RoR and Symfony.
I am unable to understand why exactly CI provides Library and Models. Most of the CI code I examined generally used Library as a Wrapper around Model. Models are exclusively kept for talking to database.
Can someone throw light on this ?
There are probably other schools of thought on this, but for me it's as follows:
Models are tightly coupled to your application, making direct references to your DB schema/architecture/file paths etc.
Libraries are loosely coupled. They should be treated like 3rd party add-ons and should make no assumptions about your app or your system. You should be able to "drop in" libraries at will with a minimum amount of configuration. Indeed, the opposite should be true, items in your library folder should be able to be dropped into any other CI application.
The basci thought on Libraries was a way to extend Codeigniter's functionality through classes.
If you compare the blank anatomy of a Library and a Model in Codeigniter, you will see that Models extend the CI_MODEL which allows you to access Codeigniter's native resources (for Example $this->db).
Libraries do not offer that basic access and they also do not need to be extended through the CI_MODEL.
Models are made to depict and interact with data (mostly abstracted from databases such as mysql).
Take a look at the basic Library
<?php defined('BASEPATH') OR exit('No direct script access allowed'); class Library{ public function MyFunction(){ //do something... } } ...and the Model anatomy
<?php defined('BASEPATH') OR exit('No direct script access allowed'); class User_model extends CI_Model { public function __construct(){ parent::__construct(); } public function MyFunction(){ //do something... } } In most cases the Models are prepared to use Ressources to access databases or other functionalities. Libraries don't. You need to include or extend the Ressources manually if you need them:
//Create an CI instance $CI =& get_instance(); Libraries are tool collections and function extensions while Models are natively ideal for abstracting and interacting with data coming from databases.