1.03

Given a Scenario, Describe Usage of di.xml

Understanding Dependency Injection configuration, which is central to Magento's architecture.

Why This Matters: The di.xml file dictates how classes are instantiated and configured using Dependency Injection (DI), giving you tremendous control over how objects are wired together.

di.xml Overview

mindmap root((di.xml)) Locations etc/ etc/adminhtml/ etc/frontend/ Nodes preference Override classes Implement interfaces type Modify constructor args xsi:type values virtualType Same code different args plugins Interceptors xsi:type Values string boolean number array object const

The Concept of Dependency Injection (DI)

What is Dependency Injection?

Core Principle: A class is provided with the resources (other classes) it needs directly in its __construct method.

Magento uses Constructor Dependency Injection

  • Classes don't call static methods or use new keyword
  • Classes simply declare what they need in the constructor
  • Magento's DI system delivers the necessary instances automatically

Purpose and Location of di.xml

The di.xml configuration file instructs the Object Manager how to manage class dependencies.

File Locations

Global: 
etc/di.xml
Applies to all areas
Admin: 
etc/adminhtml/di.xml
Admin panel only
Frontend: 
etc/frontend/di.xml
Storefront only
What You Can Do with di.xml
  1. Substitute classes using preferences
  2. Create new classes with customized arguments using virtual types
  3. Change constructor arguments for a specific class using the type element
  4. Register custom routers

Key Usages

1. Preferences (<preference>)

<preference>

Use: Substitute the requested class or interface (for) with a different concrete class (type).

<preference for="Magento\Catalog\Api\ProductRepositoryInterface"
            type="Magento\Catalog\Model\ProductRepository" />
Use sparingly: Only one preference can exist per class system‑wide.

2. Type (<type>)

<type>

Use: Modify constructor arguments for a specific class.

<type name="Bonlineco\Blog\Model\PostRepository">
    <arguments>
        <argument name="pageSize" xsi:type="number">10</argument>
        <argument name="defaultSort" xsi:type="string">created_at DESC</argument>
    </arguments>
</type>

xsi:type values

  • string, boolean, number, array, object, const

3. Virtual Types (<virtualType>)

<virtualType>

Use: Create a new configuration of an existing class with different constructor args.

<virtualType name="BonlinecoDebugLogger" type="Magento\Framework\Logger\Monolog">
    <arguments>
        <argument name="name" xsi:type="string">bonlinecoDebug</argument>
    </arguments>
</virtualType>

4. Plugins (Interceptors)

Interceptors

Plugins wrap public methods to run logic before/after/around them. Magento generates \Interceptor classes in generated/.

<type name="Magento\Catalog\Model\ProductRepository">
    <plugin name="bonlineco_blog_product_plugin"
            type="Bonlineco\Blog\Plugin\ProductRepositoryPlugin"
            sortOrder="10" />
</type>

Exam Tips

Key Points

  • Know the 3 locations for di.xml: etc/, etc/adminhtml/, etc/frontend/
  • Understand when to use <preference> vs <type> vs <virtualType>
  • Remember all 6 xsi:type values
  • Preferences are global and conflict‑prone
  • Plugins enable Interceptors and live in generated/
  • Magento uses constructor DI exclusively
Previous: 1.02 Module Structure Next: 1.04 Plugins & Observers