Magento is a modular e-commerce platform where functionality is not added by arbitrarily modifying existing code, but through clearly defined modules, configuration, and extensions.
Understanding this architecture is important for making safe changes, simplifying maintenance, and ensuring stable upgrades.
In this guide, we will explain how Magento modules, themes, and dependency injection work together. We will also cover the differences between Admin configuration, backend logic, frontend presentation, and CLI commands, as well as how to extend functionality without directly modifying files in the vendor/ directory.
What Is Magento Architecture?
Magento architecture is based on a modular approach. Each major functional area is organized as a module that can contain PHP classes, XML configuration, Admin pages, database schemas, API definitions, JavaScript, and template files.
Magento Open Source and Adobe Commerce share a large part of the same core architecture, but Adobe Commerce includes additional commercial features. Because of this, specific behavior or the availability of certain options may depend on the edition, version, and installed extensions.
A typical request passes through several layers: routing determines the controller, the service layer executes the business logic, a repository or resource model communicates with the database, while layout XML, blocks, and template files prepare the presentation.
This separation makes it possible to modify one part of the system without copying or changing the entire core codebase.
How Do Magento Modules Work?
A module is the basic unit of extension in Magento. Its identity usually consists of a vendor name and a module name, for example:
Vendor_CatalogTools
The module is registered within the Magento application and can use configuration files to connect with other parts of the system.
A typical module structure may contain directories such as:
Block
Controller
Model
Api
etc
view
Setup
Patch
Not all directories are required. The structure depends on the functionality provided by the module.
Module configuration is usually located in the etc directory. Files such as module.xml, di.xml, routes.xml, and db_schema.xml serve different purposes.
XML configuration is loaded according to its context, which means that frontend configuration does not necessarily have to be the same as configuration for adminhtml or CLI.
For functionality that belongs to your application, creating a separate custom module is recommended.
Directly modifying core modules or files inside the vendor/ directory is not a sustainable approach because those changes may be lost during an update and can make compatibility issues more difficult to resolve.
What Is Dependency Injection in Magento?
Dependency injection means that a class receives its dependencies from an external source, usually through its constructor, instead of creating them itself with the new operator.
Based on its configuration, Magento creates the required objects and passes them to the class.
A simple class may look like this:
class PriceResolver
{
public function __construct(
ProductRepositoryInterface $productRepository
) {
$this->productRepository = $productRepository;
}
}
Code language: PHP (php)The class depends on the ProductRepositoryInterface interface rather than a specific implementation of product storage.
Magento then uses its configuration to determine which implementation should be used.
This approach reduces coupling between classes and makes testing easier.
di.xml, Preference, Plugin, and Virtual Type
The di.xml file is used to define dependency injection configuration.
It can contain preferences, plugins, constructor arguments, and virtual type configurations.
Preference
A preference replaces the implementation of an interface or class with another class.
It is useful when the default implementation genuinely needs to be replaced, but it should be used carefully.
An inappropriate preference can affect every part of the system that uses that dependency.
Plugin
A plugin intercepts public methods of an existing class before, after, or around their execution.
For smaller behavior changes, a plugin is often safer than copying or replacing an entire class.
However, using too many plugins or complex around plugins can make the execution flow more difficult to understand and debug.
Virtual Type
A virtual type allows an existing class to be instantiated with a different constructor configuration without creating a new PHP class.
This can be useful for specialized configurations, but its name and purpose should be clear so that the dependency injection configuration remains understandable.
Magento Themes and the Frontend Layer
A theme determines how a Magento store is presented to visitors.
It can contain layout XML, PHTML template files, CSS or LESS styles, JavaScript, and static assets.
A theme should not contain business logic that belongs in a module.
A frontend override is used when the presentation of existing functionality needs to be changed.
Instead of modifying the original file, the appropriate file is placed inside the theme using the expected directory structure.
This allows Magento core files and extensions to remain upgradeable.
Layout XML defines the page structure, block positions, and template files that are used.
If you need to change text, element order, or visibility, layout XML is often the appropriate place to do it.
If the change requires a business decision, calculation, or access to data, the logic should remain inside a module rather than being placed in a template.
How to Choose the Right Place for a Modification
Before making a change, first determine which layer the requirement belongs to.
A setting that administrators should be able to modify should be implemented through Magento Admin and configuration.
Changes to business logic belong in a module, presentation changes belong in a theme, while server or deployment process changes belong to the infrastructure layer.
If you want to modify the result of an existing public method, check whether a plugin is sufficient.
If you need to add completely new functionality, create a module.
If you only need to modify HTML structure or styling, check layout XML and theme overrides before changing PHP logic.
Practical Development Workflow
Before starting work, create a database backup and make sure the change is tested in a development or staging environment.
Implement changes in a custom module or theme first, then check logs, cache behavior, and both frontend and Admin functionality.
To apply available module and database changes, you can use the Magento CLI command:
php bin/magento setup:upgradeThis command applies available module and database changes.
In production, it should be executed according to the deployment procedure and server role rather than being run arbitrarily while the store is operating.
To clear the Magento cache, use:
php bin/magento cache:flushThis command removes cached data from the configured cache backends.
Before running it, verify that the issue is actually cache-related because flushing the cache may temporarily increase system load while the cache is being rebuilt.
Advantages and Limitations of Magento Architecture
Magento’s modular architecture makes it possible to extend functionality without modifying core code, provides clearer separation of responsibilities, and simplifies the maintenance of larger projects.
Dependency injection makes replacing implementations and writing tests easier, while themes separate presentation from business logic.
The main limitation is complexity.
A large number of modules, preferences, plugins, and XML configuration files can make it difficult to identify the source of a problem.
Incompatible extensions can cause conflicts, while an incorrect override may affect more pages than originally expected.
Common Problems
One common mistake is modifying files inside the vendor/ directory.
Although such a change may solve a problem immediately, it is not permanent and makes future upgrades more difficult.
Depending on the goal, a better approach is to use a custom module, plugin, preference, or theme override.
Another common problem is attempting to implement business logic inside a PHTML template.
A template should display prepared data, while more complex logic should be implemented in the appropriate PHP class or service.
Dependency injection problems often occur because of an incorrect namespace, a missing class, an incompatible preference, or a constructor definition that changed after an upgrade.
Before making major changes, check the exception logs, module configuration, and extension compatibility.
Recommended Practices for a Maintainable Magento Project
Keep custom code inside your own modules and themes, use Composer to manage dependencies, and keep track of extensions that modify the same classes or layout handles.
Avoid global preferences when a plugin or service contract can solve the requirement with less risk.
Test changes in an environment that resembles production as closely as possible.
After deployment, check:
- Frontend
- Checkout
- Customer account
- Admin panel
- Indexers
- Cache
- Relevant logs
Pay particular attention to differences between developer and production modes.
Should You Modify Magento Core Code?
No.
Core modifications are not recommended because they can be lost during upgrades.
Use a custom module, plugin, preference, or theme override depending on the requirement.
When Should You Use a Plugin and When Should You Use a Preference?
A plugin is appropriate for intercepting a public method and making a smaller change to its behavior.
A preference replaces a specific implementation and can therefore have a much broader impact.
Preferences should only be used when such a replacement is genuinely necessary.
Can a Theme Contain Business Logic?
Business logic inside a theme should be avoided.
A theme is intended for presentation and frontend resources, while business logic belongs in a module, service, or another appropriate class.
Can the Same Module Be Used in Magento Open Source and Adobe Commerce?
It depends on the module’s functionality and requirements.
A module that uses only Magento components shared by both editions may work with Magento Open Source and Adobe Commerce.
However, commercial features and edition-specific APIs require additional compatibility checks.
What Should You Check First When a Change Does Not Work?
Check whether the module is enabled, whether the XML configuration is defined in the appropriate area, whether the cache has been cleared, and whether static files have been regenerated when necessary.
Then review the Magento and PHP logs.
Magento architecture relies on modules for functionality, themes for presentation, and dependency injection for connecting objects.
The safest development approach is to place every modification in the appropriate layer without directly modifying Magento core or vendor/ code.
For practical development, first identify where the requirement belongs and then choose the least invasive solution: configuration, plugin, service, custom module, or theme override.
