How to override core functions of Magento

Table of Contents1) Overview of Magento architecture (3)1.1) Base knowledge about MVC (3)1.2) Modules make a Magento website (3)1.3) What is included in a module? (5)2) Overriding a module (8)2.1) Two different of way (8)2.1.1) The first way (8)2.1.2) The second way (9)2.2) Conclusion (11)3) Overriding Core Blocks (13)4) Overriding Core Models (13)5) Overriding Core Helpers (14)6) Overriding Core Controllers (15)1)Overview of Magento architecture1.1)Base knowledge about MVCMagento is based on MVC structure.MVC is a popular design pattern which is using in software development and web development; it demands us to implement an application by three layers:∙M = Model Layer. The model handles the data. F or example, it’s in charge of CRUD operation of database (Create-Read-Update-Delete).∙V = View Layer. The view handles the display to the user. For example, PHTML template in Magento.∙ C = Controller Layer. The controller is the “bridge” between the model and the layer, it is in charge to find the right model to handle data processing according to the user’s request, and find the right view to display the result to the user.1.2)Modules make a Magento websiteModules are the core of Magento. Every action on the site, frontend or backend, goes through a module. Modules act as containers for one or more of the following:∙Settings∙database schemas∙Rendering objects∙Utility helpers∙Data models∙Action controllers.A module can be made of all six of these things, or just one.Modules are defined as being on or off in an XML configuration system located in app/etc/modules/. Each module can specify its own settings in an XML file as well, located under the module’s etc/ directory.Since everything in Magento is a module, and modules have self-contained configuration and database settings, this allows us to extend Magento exactly as the core system is built.Here is a preliminary core modules dependency diagram, each package here is a module:Source: /wiki/doc/magento-architectureTo have a good overview, let’s go into the core directory of Magento: /app/code/core/Mage. There we can see a lot of folders. Actually, each folder is a module:1.3)What is included in a module?Let’s have a look at a general structure of a module. Here is the content of folder /app/code/core/Mage/Catalog:∙Block: PHP files which are relate with a specific block in front page, it provides a few functions to the template related.∙Controllers: In charge of handle a specific client request. After business processing, controller chooses a suitable template and render the template, and then, response the result to client’sbrowser.∙Etc: The xml file configuration of the module, it declares which model and block is included in this module, sets the default parameter value for some configurable option etc.∙Helper: provides some useful utilities to Blocks, templates etc. such like image resize, string cutting etc.∙Model: in charge of handle database and entity object, the model class can be called by Bocks, controllers or other Models.∙Sql: PHP files, it used to install or upgrade database if necessary, we can write SQL script in it. Another part of a module is stored in the design folder, here is the content of/app/design/frontend/default/default/∙Layout: configuration xml file, we can used it to construct page by different flexible blocks.∙Locale: CSV translation file∙Template: phtml file, we can write PHP and HTML in it, it uses the functions of block to fill data dynamically. The related pages of each module are stored in the folder which named withmodule’s name.For each request from client browser, how does Magento work? Let’s have a look at the diagram below:Source: /wiki/doc/magento-architectureAs we can see in the diagram above, Magento implements the MVC structure by some different components.∙Controllers is in charge of Controller Layer∙Layerout, block, template and helper is in charge of View Layer∙Model is in charge of Model Layer2)Overriding a moduleIf you find that you need to change the behavior of core functions such as Models, Blocks, Helpers, etc. sometimes you need to add a function to a Core class of Magento, sometimes you need to modify a function. 2.1) Two different of wayLet’s take an example: b y default, in category page of Magento, there is a RSS Feed link beside of the category title, only if the current level of the category is 2, which means the category is a direct subcategory of root category (ex: Furnitur e in Magento Demo). If the category is not level 2, it won’t display RSS Feed link (Ex: Living Room in Magento Demo).Now, we want to change this, we want to see RSS Feed link in category Living Room but in category Furniture. So we need to modify core function of Block.2.1.1) The first wayCopy the Core source code which you want to modify in the directory /app/code/local/Mage, and make the directory structure as same as it looks under /app/code/core/Mage. For example, here is a part of the source code of: /app/code/core/Mage/Catalog/Block/Category/View.phpWe want to change the function IsTopCategory() to make it like this:You just need to copy View.php from /app/code/core/Mage/Catalog/Block/Category to/app/code/local/Mage/Catalog/Block/Category, and then modify the line which you want to change.After the step, you will see the result of your modification immediately.2.1.2) The second wayWe still use the sample above.∙Create the following directory structure:/app/code/local/Bysoft/Catalog/Block/Category//app/code/local/Bysoft/Catalog/etc/∙Build the config.xmlEvery module needs a configuration file. This file is located under the etc/ subdirectory, here is the source of config.xml in this sample.As you can see, we will override the “Category/View.php” block inside the “Catalog” Module. Note that the underscores represent the directory structure the core block is in(“Bysoft_Catalog_Block_Category_View refers to Bysoft/Catalog/Block/Category/View.php).∙Create the BlockAs you can see in the config.xml file, we have to create a new file named View.php in the Block/ subdirectory. Here is the content of the file:As you can see, we create a new block class which extends the core block class. That means your new class will have all the properties and functions the core class has. All functions you put in your class will be used instead of the ones from the core, and you can also add completely new functions to it. For now we just replaced the IsTopCategory() function.∙Load your moduleNow we finished our module, but Magento doesn’t know of it s existence yet. We have to create a file in/app/etc/Modules that loads our module. Name that file Bysoft_Catalog.xml. Here is the content of the file:All xml files inside /app/etc/Modules will be loaded automatically. By placing the above file in that directory, Magento will know that it has to look for a config.xml in /app/code/local/Bysoft/Catalog/etc and load our new module2.2) ConclusionIt seems that the first way is easier to do, but recommend the second way. Here are the reasons.Actually, the first way is not a kind of overriding, it just only implements some core functions outside of the Magento core directory. If we want to modify a function from the Core module class using this method, we need to copy the whole directory structure where the class belongs into /app/code/local/Mage/…. We must keep all the source code in that file and just modify the function we want, because the classes under /app/code/local have higher priority than classes under /app/code/core. So Magento will not see the class under directory/app/code/core/Mage that has the same name and same directory structure as the one in app/code/local. T he first disadvantage is that people can’t distinguish easily what has been modified.If we upgrade Magento, using Magento Connect or manually, it will also bring some problems, the reason is the same as we mentioned above. For example, here is a Magento core code with version 1.2.1, the path of the file is /app/code/core/Mage/Catalog/Model/Product.phpWe want to modify the function a(). Using the first way, we put the file here:/app/code/local/Mage/Catalog/Model/Product.php, and change the file’s content like this:Now, we want to upgrade Magento from 1.2.1 to 1.3.0, we use Magento Connect to do it, after upgrade, the content of file /app/code/core/Mage/Catalog/Model/Product.php is like figure below:As you can see in the figure, The new version of Product.php has deleted the function b() and added a function d(), but the modification can’t take effect in Magento, because it will still use the file/app/code/local/Mage/Catalog/Model/Product.php.So the second disadvantage is that Magento upgrade will be affected by our modification on core functions.Not all of the components can be rewrite with the first way, for example, if you want to change some configuration in config.xml which is under core module, and if you follow the first way to do it, your modification won’t work, you have to choose the second way. Excepti ng configuration file, Core Controller also can’t be rewrite using the first way.3)Overriding Core BlocksA block is a PHP file that is used in the template files (*.PHTML).The example at paragraph 2.1.2 explains how overriding a Core Block. To sum up:∙Create directory structure∙Build the config.xml∙Create the block∙Load your module4)Overriding Core ModelsA Model in Magento is a PHP class file which is used to handle database or data entity. The way ofoverride a Model is as same as overriding a Block. The different is just in the configuration xml file, here is an example.We can judge by this diagram that there must be a file named Product.php which is saved under/app/code/local/Bysoft/Catalog/Model/. This file is the new model class which extends the core model class.5)Overriding Core HelpersHelpers are the PHP files which can provide some common functions for Blocks or templates, it is a series of helper classes which is used to handle string, image or something else.It is the same as overriding Core Blocks and Core Models, here is sample of config.xmlSo it must be a PHP file named Category.php under app/code/local/Bysoft/Catalog/Helper which extends Mage_Catalog_Helper_Category.6)Overriding Core ControllersA Controller is an entrance of a client request, it analyzes client’s request and chose related Models to handle the business logic, and then it renders an appointed template file by some Blocks, at last, it displays the right result to client’s browser.Compare to Blocks, Models and Helpers, it is more complicated to override a Core Controller. In this example, we are going to override: Mage_Checkout_CartController::indexAction().We didn’t do any business modification of the original controller in this sample, we just want to validate if our new controller take effect or not.∙Create your module folders and files∙/app/code/local/Bysoft/Test/etc/config.xml∙/app/code/local/Bysoft/Test/controllers/Checkout/CartController.php∙/app/etc/modules/Bysoft_Test.xml∙Edit /etc/config.xmlHere is content of file /app/code/local/Bysoft/Test/etc/config.xml∙<Bysoft_test_checkout_cart>: Is the classname in your own controller∙<From>: Original route matches the path to your controller∙<to>: If matches successfully , it will use your controller.∙<frontend>: We need to indicate this if this is a frontend controller. If it is backend Controller, it will be replaced with <adminhtml>∙<use>: For a backend controller, Just change the value “standard” to “admin”.∙Edit /controllers/Checkout/CartController.php∙Edit /app/etc/modules/Bysoft_Test.xml∙Edit /app/design/frontend/[myinterface]/[mytheme]/layout/checkout.xmlAdd the following to use the same update handle as before:∙Point your browser to /checkout/cart/All things are done, and then, we can check if it works:∙Enable system log( go to BO, System->Advanced->Developer->log settings)∙Clean cache( delete folder /var/cache)∙C lick the link ‘My cart’ on the top of index page of Magento∙Go into directory /var/log, have a check if there is a file named system.log and if the file contain a line with string ‘haha!’, congratulations! You successfully override the Core Controller.。