DEPENDENCY INJECTION in MAgento 2

Agenda

1. Motivation
2. Object Composition
3. Object Lifestyle
4. Interception

Motivation:

• Complexity
• Software Entropy

Wrong Approach

Problems with service location

• Implicit dependencies
• God classes
• Code coupling made easy

Complexity Made Easy

Complex things should be hard to do in application while simple things should be easy. 

~Rich Hickey

Solution

• Explicit dependencies
• Honest interfaces
• Controlled code coupling
• Unit testable code

Pillar 1: Object Composition

class Magento_Acl_Resource
{
    protected $_resourceProvider;
    
    protected $_resourceFactory;
    
    public function __construct(
        Magento_Acl_ResourceProvider $resourceProvider,
        Magento_Acl_ResourceFactory $resourceFactory,
        $prefix = 'prefix'
    ) {
        $this->_resourceProvider = $resourceProvider;
        $this->_resourceFactory = $resourceFactory;
        $this->_prefix = $prefix;
    }
}

Composition ROOT

http://blog.efvincent.com/di-bootstrap/

class Magento_Acl_Resource
{
    protected $_resourceProvider;
    
    protected $_resourceFactory;
        
    public function __construct(
        Magento_Acl_ResourceProvider $resourceProvider,
        Magento_Acl_ResourceFactory $resourceFactory,
        $prefix = 'prefix'
    ) {
        $this->_resourceProvider = $resourceProvider;
        $this->_resourceFactory = $resourceFactory;
        $this->_prefix = $prefix;
    }
}

class Magento_Acl_Resource
{
    protected $_resourceProvider;
    
    protected $_resourceFactory;
    
    public function __construct(
        Magento_Acl_ResourceProviderInterface $resourceProvider,
        Magento_Acl_ResourceFactory $resourceFactory,
        $prefix = "somePrefix"
    ) {
        $this->_resourceProvider = $resourceProvider;
        $this->_resourceFactory = $resourceFactory;
        $this->_prefix = $prefix;
    }
}

<config>
    <type name="Magento_Acl_Resource">
        <param name="resourceProvider">
            <instance type="Magento_Acl_ResourceProvider" />
        </param>
    </type>
</config>

<config>
    <preference for="Magento_Acl_ResourceProviderInterface"
                type="Magento_Acl_ResourceProvider" />
</config>

Virtual Types

<config>
    <virtualType name="customAclResource" type="Magento_Acl_Resource">
        <param name="prefix">
            <value>someOtherPrefix</value>
        </param>
    </virtualType>
    <type name="Magento_Acl_Builder">
        <param name="resource">
            <instance type="customAclResource"/>
        </param>
    </type>
</config>

Pillar 2: Object Lifetime

• Injectables
• Non-Injectables

Injectables

• Mostly services or value objects
• Mostly stateless
• Mostly singletons
• Can be shared or non-shared
• Don't confuse with Singleton Pattern

Non-shared injectable

<config>
    <type name="Magento_Acl_ResourceProvider" shared="false" />
</config>

<config>
    <type name="Magento_Acl_Resource">
        <param name="resourceProvider" shared="false" />
    </type>
</config>

Factories

• Created for non-injectables
• Are injectables
• Can be auto-generated

Optional dependencies

class Magento_Acl_Resource
{
    protected $_resourceProvider;
    
    protected $_resourceFactory;
    
    public function __construct(
        Magento_Acl_ResourceProviderInterface $resourceProvider,
        Magento_Acl_ResourceFactory $resourceFactory,
        $prefix = "someId"
    ) {
        $this->_resourceProvider = $resourceProvider;
        $this->_resourceFactory = $resourceFactory;
        $this->_prefix = $someId;
    }
}

Proxies

• Object-oriented way to do lazy-loading
• Resposible for lazy-loading only
• Can be auto-generated

<config>
    <type name="Magento_Acl_Resource">
        <param name="resourceProvider"
               type="Magento_Acl_ResourceProviderProxy" />
    </type>
</config>

Pillar 3: Interception

Interception Description

Interception Demo

Interception Limitations

• Private calls
• Methods with final classes
• Performance

The book

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