Developing Loosely Coupled Modules with Magento
- 6. General Task of Injecting into Functionality
- 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 A if (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 modules Module C Notify Notify Register
- 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 anything Module C Messages Manager Publish Subscribe Call Subscribe Call
- 12. Magento Events
- 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 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 • Mapping events to handling routines • Declaration of handlers for each application 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) { // ... }
- 23. Framework High Modules Coupling Mage_Cron Removing Mage_Cron breaks My_Module My_Module Schedule Job Get Schedule & Run Job
- 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
Editor's Notes
- #11: Observer OOP pattern is a subset of the publish/subscribe messaging pattern observers subscribe to the particular subjects
- #13: OOP implementation of pub/sub pattern is the single global event manager
- #19: Convention over Configuration
- #20: Convention over Configuration
- #26: Cron job scheduling through config.xml
- #28: Let’s summarize what we have learned during this hour.