magento-di

Magento 2 Dependency Injection

Before writing code

Fetch live docs:

1. Web-search site:developer.adobe.com commerce php development components dependency-injection for the DI guide
2. Fetch https://developer.adobe.com/commerce/php/development/ and navigate to DI documentation
3. Web-search site:developer.adobe.com commerce php development build di-xml for di.xml reference

Conceptual Architecture

How DI Works in Magento

Magento's Object Manager reads di.xml configurations and automatically injects dependencies into class constructors. You declare what you need; the framework provides it.

Constructor injection is the primary pattern — declare dependencies as constructor parameters with type hints.

di.xml Scope

di.xml files are area-scoped:

• etc/di.xml — global (all areas)
• etc/frontend/di.xml — storefront only
• etc/adminhtml/di.xml — admin panel only
• etc/webapi_rest/di.xml — REST API only
• etc/webapi_soap/di.xml — SOAP API only

Types

Configure constructor arguments for a specific class:

• Override default values
• Inject different implementations per area
• Argument types: string, boolean, number, const, null, object, array, init_parameter

Virtual Types

Create class variations without writing new PHP files:

• Same base class with different constructor arguments
• Only exists in DI configuration
• Cannot be injected by classname directly (use as a type attribute value)
• Reduces code duplication significantly

Preferences

Map an interface to a concrete implementation:

• <preference for="InterfaceName" type="ConcreteClassName" />
• Global preference applies everywhere unless overridden by area-specific di.xml
• Foundation of Magento's interface-based programming

Argument Types

Type	Description
string	String value
boolean	true or false
number	Integer or float
const	PHP constant value
null	Null value
object	Another class instance (injected)
array	Array of mixed argument types
init_parameter	Value from Magento\Framework\App\DeploymentConfig

Shared vs Non-Shared

• By default, Object Manager creates shared instances (singleton behavior)
• Set shared="false" on a type to get a new instance each time
• Factories (SomeClassFactory) always create new instances

Sensitive/Environment Config

init_parameter type reads from app/etc/env.php — use for environment-specific values that shouldn't be in di.xml.

Common Patterns

• Interface → Implementation mapping: preference for repository, data, and service interfaces
• Logger customization: virtual type with custom handler arguments
• Collection modification: type with different filter arguments per area
• Plugin declaration: type with plugin child element (covered in plugins skill)

Best Practices

• Always inject interfaces, not concrete classes
• Use virtual types to avoid unnecessary PHP files
• Scope di.xml to the smallest applicable area
• Never call Object Manager directly in application code (only in factories and framework)
• Use shared="false" sparingly — most dependencies should be shared

Fetch the DI documentation for exact XML schema, element attributes, and current best practices before configuring.