Magento 2 is built around the Dependency Injection principle. It is a lot more than retrieving classes through the constructor which already leads to better code quality. Do you know all the ways how you can modify the class hierachy in Magento 2? How do they work, in which cases are they beneficial? Fully understanding how Dependency Injection and the Object Manager work is key to advanced Magento 2 backend development. The talk will start with a broad overview of Dependency Injection in general and in Magento 2. Afterwards, Andreas will explain the details and show easy-to-understand examples, based on real-life projects and on his experience as a Magento 2 trainer.

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Dependency Injection Extended
The Way to advanced Magento 2 Development
September 10th 2018 – Meet Magento PL
Andreas von Studnitz – integer_net – @avstudnitz

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Andreas von Studnitz
Co-Founder and Managing Director @ integer_net
Magento Developer, Trainer, Consultant
since 2008
Twitter: @avstudnitz

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Purpose of DI

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All dependencies in one place
Make testing easier
Better readable code

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Basics

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Constructor Injection

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How does it work?

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Classes are not instantiated
with new() in Magento 2

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The Object Manager is
used instead

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Instantiate a new class (1)
Does an object of that type
already exist?
Reuse existing object Create new object
Yes No
Get type from constructor parameter

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Constructor Injection

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The next Steps

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Injecting an Interface?

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Injecting an Interface?

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Define a Preference!
<module_directory>/etc/di.xml

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Instantiate a new class (2)
Get type from constructor parameter
Does an object of that type
already exist?
Reuse existing object Create new object
Yes No
Does a preference exist?
Yes NoUse preference
as type

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Arguments

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Scalar Arguments

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Scalar Arguments
<module_directory>/etc/di.xml

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Basic Argument Types
string
number
boolean
array
null

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Advanced Argument Types
const
object
<module_directory>/etc/di.xml
<module_directory>/etc/adminhtml/di.xml

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A typical Usecase

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A typical Usecase
<module_directory>/etc/di.xml

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A typical Usecase
<module_directory>/etc/di.xml

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A typical Usecase

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Virtual Types

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Virtual Types
Re-use an existing Class
With different Arguments

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Example

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Example

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Some advice about Virtual Types
Complexity
Naming
Add “Virtual” to identifier
Only use Virtual Types if really necessary

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DI and Blocks

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Arguments
module-catalog/view/frontend/layout/catalog_product_view.xml
module-catalog/view/frontend/templates/product/list/items.phtml

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View Models
module-catalog/view/frontend/layout/catalog_product_view.xml
module-catalog/view/frontend/templates/product/breadcrumbs.phtml
Read more: https://www.integer-net.com/view-models-in-magento-1-and-2/
(by Fabian Schmengler)

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Remarks
This only works for Magento 2.2+
The view model MUST implement
Don’t overdo it!

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DI for Blocks
Preferences
Arguments
Virtual Types

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A little Helper

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A little Helper

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A little Helper

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Conclusion
Composition over Inheritance
A mighty Toolset
Use with care

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“
#MM18PL
“Debugging is twice as hard as
writing the code in the first place.
Therefore, if you write the code as
cleverly as possible, you are, by
definition, not smart enough to
debug it.”
- Brian Kernighan

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Thank you!
Any Questions?
avs@integer-net.de
@avstudnitz
@integer_net
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