Presentation at Magento Developers Paradise 2011

1. Click to edit Master title style
Ibiza, June 4th – 7th 2011

2. Magento Developers Paradise
Developing Loosely Coupled Modules with
Magento
Sergey Shymko
Magento 2 Team

3. Introduction and Terminology
• Coupling or dependency is the degree to
which each program module relies on
each one of the other modules
• Coupling measures the likelihood of a
change or fault in one module affecting
another module

4. Module Purpose/Behavior
• Module introduces new feature
• Module injects into existing functionality
• Module integrates with existing feature
• Module extends/overlaps existing
functionality

5. Magento Developers Paradise
Modules Coupling While
Injecting Into the Functionality

6. General Task of Injecting into Functionality
• Module A exists and already implements
the functionality
• Module B expands the Module A
• Module B should be triggered at the
specific point of the Module A execution

7. Hard-Coded Call Implementation
Framework
Module A Module B
Call
• Module A highly relies
on Module B
• Module B
can’t be removed

8. Conditional Call Implementation
Framework
Module A Module B
Call
• Module existence
checking
• Module B now
can be removed
• Module A still knows
about Module B
• Rename Module B –
change Module A
• Add new module –
change Module Aif (exists(‘Module B’)) {
call(‘Module B’);
}
Module C

9. Maintaining the List of Dependents
Framework
Module A Module B
Register
• It’s observer pattern
• Module B
relies on Module A
• New modules can
register within the
Module A without
changing anything
• Rename Module A –
change dependent
modulesModule C
Notify
Notify
Register

10. Publish/Subscribe Messaging Pattern
• Pub/sub – universal decoupling solution
– senders of messages do not program the
messages to be sent directly to specific
receivers
– subscribers express interest in messages
without knowledge of publishers

11. Low Modules Coupling Using Pub/Sub Pattern
Framework
Module A Module B
• Framework should
take care of coupling
• Modules don’t know
about each other
• Any module can be
removed
• New modules can
subscribe to existing
messages without
changing anythingModule C
Messages Manager
Publish
Subscribe
Call
Subscribe
Call

12. Magento Events
• Magento events – object-oriented
implementation of the pub/sub pattern
• Event dispatching calls – points of
integration
• Subscription through config.xml

13. Framework
Low Modules Coupling with Magento Events
Module A
Subscribe
Module B
Call
config.xml
Config Manager
config.xml
Merged config.xml
Events Manager
Mage::dispatchEvent

14. Achieved Coupling with Magento Events
Coupling depends on the implementation of the particular event handler
Coupling Type Description
Message coupling (low) Event doesn’t pass any data
Data coupling Simple event parameters, each is used
Stamp coupling Event data structure contains fields which may or
may not be used
Common coupling Usage of the global data registry; Accessing data
not only through methods
Content coupling (high) Not applicable to the pub/sub

15. Possible Improvements in Magento Events
• Strict event data types
• Convention over configuration
• Events naming convention

16. Strict Event Data Types
• Own event class for each unique
parameters combination
‒ Formal data structure declaration
‒ Access restriction to event data
‒ Events documentation auto-generation

17. Convention over Configuration
• Also known as coding by convention
• Decreasing the number of decisions that
developers need to make
• Simplicity while keeping flexibility
• Providing good defaults

18. Events Subscription in Configuration
• Mapping events to
handling routines
• Declaration of handlers
for each area
<events>
<catalog_product_load_after>
<observers>
<inventory>
<class>cataloginventory/observer</class>
<method>addInventoryData</method>
</inventory>
</observers>
</catalog_product_load_after>
class Mage_CatalogInventory_Model_Observer
{
public function addInventoryData($observer)
{
// ...
}

19. No Events Subscription in Configuration
• Good default mapping
• Single observer class
per module
• Method name equals
event name
<config>
<global>
<events/>
</global>
<frontend>
<events/>
</frontend>
<adminhtml>
<events/>
</adminhtml>
</config>
class Mage_CatalogInventory_Model_Observer
{
public function catalog_product_load_after($observer)
{
// ...
}

20. Event Naming Convention
Event Name Part Description
1. Module Name of the module, which introduces an event.
2. Layer Application layer where an event appears.
Allowed values: model, view, controller, service.
3. Entity Entity (domain) to which event has relation.
4. Action By default action should be equal to the method name,
which triggers an event.
[5. Suffix] Optional. Allowed values: before, after
lowerCamelCase event name to correspond to the method name

21. Magento Developers Paradise
Modules Coupling While
Integrating with Existing Feature

22. Sample Task – Cron Feature
• Module Mage_Cron introduces time-based
jobs scheduling feature
• Any module should be able to schedule its
jobs

23. Framework
High Modules Coupling
Mage_Cron
Removing Mage_Cron breaks My_Module
My_Module
Schedule Job
Get Schedule & Run Job

24. Magento Configuration Files
• Configuration files “merging” from all
enabled modules
• Configuration allows integration with:
– system-wide feature
– feature provided by the module

25. Framework
Low Modules Coupling Using Configuration
Mage_Cron
config.xml
My_Module
config.xml
GetSchedule
Run Job
Removing Mage_Cron doesn’t break anything
Config ManagerMerged config.xml
ScheduleJob

26. Configuration Usage in Magento
• Cache management
• Index management
• Product types
• Translation files
• Layout files
• …

27. Magento Developers Paradise
Summary

28. Recommendations
• Follow the low coupling principles – use
events to communicate between modules
• Extend only when no events are triggered
• Report requests for adding new events
• Don’t hesitate to trigger events in your
third-party modules and extensions

29. Magento Developers Paradise
Thank You!
Sergey Shymko
sergey.shymko@magento.com
Questions & Answers