Commerce framework

The Adobe Commerce and Magento Open Source framework (Commerce framework) controls how application components interact, including request flow, routing, indexing, caching, and exception handling. It provides services that reduce the effort of creating modules that contain business logic, contributing to the goal of both making Commerce code more modular as well as decreasing dependencies.

This primarily PHP software component is organized into logical groups called libraries, which all modules can call. Most of the framework code sits under the domain layer or encloses the presentation, service, and domain layers. The framework contains no business logic. (Although the Commerce framework does not contain resource models, it does contain a library of code to help implement a resource model.)

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Don't confuse the Commerce framework with the Zend web application framework that ships with the Commerce framework.

You should never modify framework files, although if you are extending Commerce, you must know how to call framework libraries. Modules you create will typically inherit from classes and interfaces defined in the framework directories.

Responsibilities

The Commerce framework provides libraries that help reduce the effort of creating modules that contain business logic.

The Framework is responsible for operations that are useful for potentially all modules, including:

handling HTTP protocols
interacting with the database and filesystem
rendering content

Organization

Here is the Commerce framework folder structure:

vendor/
    ../magento
        ../framework
lib/
    ../internal
        ../LinLibertineFont
    ../web

/vendor/magento/framework contains only PHP code. These are libraries of code plus the application entry point that routes requests to modules (that in turn call the Framework libraries). For example, libraries in the Framework help implement a resource model (base classes and interfaces to inherit from) but not the resource models themselves. Certain libraries also support CSS rendering.
/lib/internal contains some non-PHP as well as PHP components. Non-PHP framework libraries includes JavaScript and LESS/CSS.
/lib/web contains JavaScript and CSS/LESS files. These files reside under web and not internal because they are accessible from a web browser, while the PHP code under internal is not. (Any code that a web browser must access should be under web, while everything else under internal.)

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The vendor/magento/framework directory maps to the Magento\Framework namespace.

Framework highlights

The Commerce framework (lib/internal/Magento/Framework/) provides a robust range of functionality. If you are an extension developer, you may be interested in this subset of Framework namespaces.

Namespace

Purpose

Magento\Framework\DataObject

Provides standard functionality for storing and retrieving data through magic methods. This is the base class for many classes.

Magento\Framework\View

Contains code to render pages and layouts.

Magento\Framework\Url

Contains code to look up other pages.

Magento\Framework\Controller

Contains classes to help return different types of results (for example, JSON and redirects).

Magento\Framework\Model

Contains base Model classes that almost all model classes extend from.

Magento\Framework\Data

Contains additional classes that handle forms.

Magento\Framework\Model\AbstractModel

Magento\Framework\Model\ResourceModel\AbstractResource

Other namespaces under Magento\Framework that will interest extension developers:

Namespace

Purpose

Magento\Framework\ObjectManager

Used to provide dependency injection.

Magento\Framework\App

Contains framework code that has knowledge about the Commerce application. This code bootstraps the application and reads in the initial configuration. It also contains the entry point to the command line tools, the web application, and the cron job. And finally, it routes requests while providing the deployment context (such as reading in the configuration for the database configuration, languages, and caching systems).

Magento\Framework\Api

Contains base classes for advanced functionality of extendable objects through the system (that is, objects that can be extended to add new data through Commerce Marketplace extensions).

Magento\Framework\Config

Contains the generic configuration reader. Each config file has its own specialized reader extending these classes.

Magento\Framework\Filesystem

Contains classes that handle reading from and writing to the file system.

Magento\Framework\HTTP\PhpEnvironment

Magento\Framework\Session

Magento\Framework\Stdlib\Cookie

Code to handle the HTTP request/responses as well as session/cookies is found here.

Magento\Framework\Exception

Contains the basic exceptions that are thrown throughout the Commerce codebase.

Magento\Framework\Event

Contains the code that publishes synchronous events and that handles observers for any Commerce event is handled here.

Magento\Framework\Validator

Contains the code that validates data (currencies, not empty) and that handles observers for any Commerce event.