The document outlines a modular framework for managing dependencies between modules, emphasizing low coupling through publish/subscribe patterns and event subscriptions. It discusses the conditional implementation of module calls, renaming modules, and the observer design pattern for notifying dependent modules without altering existing structures. The framework also addresses best practices for event handling and configuration management to maintain modular integrity within applications.

3. Introduction and Terminology

4. Module Purpose/Behavior

6. General Task of Injecting into Functionality

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

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

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

10. Publish/Subscribe Messaging Pattern

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

12. Magento Events

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

14. Achieved Coupling with Events
Actual coupling depends on the implementation of the
particular event handler:
Message coupling (low)
Data coupling
Stamp coupling
Common coupling
…
Content coupling (high)

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

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

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

25. Low Modules Coupling Using Configuration
Framework
Merged config.xml Config Manager
Get Schedule
Schedule Job
Mage_Cron My_Module
config.xml config.xml
Run Job
Removing Mage_Cron doesn’t break anything

29. sergey.shymko@magento.com