Events

What are Events in Open Register?

In Open Register, Events are notifications that are triggered when significant actions occur within the system. They form the foundation of Open Register's event-driven architecture, enabling loose coupling between components while facilitating rich integration possibilities.

Events in Open Register are:

• Triggered automatically at key points in the application lifecycle
• Standardized messages containing relevant data about what occurred
• Available for other components to listen and respond to
• Essential for building extensible, integrated systems
• Compatible with Nextcloud's event dispatcher system

Event Structure

An event in Open Register consists of the following key components:

Component	Description
Event Class	The PHP class that defines the event type
Event Data	The data payload carried by the event
Timestamp	When the event occurred
Source	The component that triggered the event
Context	Additional contextual information

Event Categories

Open Register provides several categories of events:

1. Schema Events

Events related to schema lifecycle:

• SchemaCreatedEvent: Triggered when a new schema is created
• SchemaUpdatedEvent: Triggered when a schema is updated
• SchemaDeletedEvent: Triggered when a schema is deleted

2. Register Events

Events related to register lifecycle:

• RegisterCreatedEvent: Triggered when a new register is created
• RegisterUpdatedEvent: Triggered when a register is updated
• RegisterDeletedEvent: Triggered when a register is deleted

3. Object Events

Events related to object lifecycle:

• ObjectCreatedEvent: Triggered when a new object is created
• ObjectUpdatedEvent: Triggered when an object is updated
• ObjectDeletedEvent: Triggered when an object is deleted

4. File Events

Events related to file operations:

• FileUploadedEvent: Triggered when a file is uploaded
• FileUpdatedEvent: Triggered when a file is updated
• FileDeletedEvent: Triggered when a file is deleted

5. Validation Events

Events related to validation:

• ValidationSucceededEvent: Triggered when validation succeeds
• ValidationFailedEvent: Triggered when validation fails

Example Event

Here's an example of an ObjectCreatedEvent:

namespace OCA\OpenRegister\Event;

use OCA\OpenRegister\Entity\ObjectEntity;
use OCP\EventDispatcher\Event;

class ObjectCreatedEvent extends Event {
    private ObjectEntity $object;

    public function __construct(ObjectEntity $object) {
        parent::__construct();
        $this->object = $object;
    }

    public function getObject(): ObjectEntity {
        return $this->object;
    }
}

Event-Driven Architecture

Open Register uses an event-driven architecture to provide several benefits:

1. Loose Coupling

Components can interact without direct dependencies:

• The event publisher doesn't need to know who is listening
• Listeners can be added or removed without changing the publisher
• Different parts of the system can evolve independently

2. Extensibility

The event system makes Open Register highly extensible:

• New functionality can be added by listening to existing events
• Third-party applications can integrate without modifying core code
• Custom business logic can be implemented through event listeners

3. Scalability

Event-driven architectures support better scalability:

• Processing can be distributed across different components
• Asynchronous handling allows for better resource management
• Event queues can buffer processing during peak loads

4. Observability

Events provide better system observability:

• System activities can be monitored through events
• Audit trails can be built by capturing events
• Debugging is easier with a clear event timeline

Working with Events

Listening to Events

To listen to events in Open Register, you need to:

1. Create an event listener class
2. Register it with Nextcloud's event dispatcher

Here's an example of a listener for ObjectCreatedEvent:

namespace OCA\MyApp\Listener;

use OCA\OpenRegister\Event\ObjectCreatedEvent;
use OCP\EventDispatcher\Event;
use OCP\EventDispatcher\IEventListener;

class ObjectCreatedListener implements IEventListener {
    public function handle(Event $event): void {
        if (!($event instanceof ObjectCreatedEvent)) {
            return;
        }
        
        $object = $event->getObject();
        // Perform actions with the new object
    }
}

Registering Event Listeners

Register your listener in your app's Application.php file:

use OCA\OpenRegister\Event\ObjectCreatedEvent;
use OCA\MyApp\Listener\ObjectCreatedListener;
use OCP\EventDispatcher\IEventDispatcher;

// In the register() method:
$dispatcher = $this->getContainer()->get(IEventDispatcher::class);
$dispatcher->addServiceListener(ObjectCreatedEvent::class, ObjectCreatedListener::class);

Dispatching Events

If you're extending Open Register, you might need to dispatch your own events:

use OCA\OpenRegister\Event\CustomEvent;
use OCP\EventDispatcher\IEventDispatcher;

// Inject the event dispatcher
private IEventDispatcher $eventDispatcher;

public function __construct(IEventDispatcher $eventDispatcher) {
    $this->eventDispatcher = $eventDispatcher;
}

// Dispatch an event
public function performAction() {
    // Do something
    $event = new CustomEvent($data);
    $this->eventDispatcher->dispatch(CustomEvent::class, $event);
}

Event Relationships

Events have important relationships with other core concepts:

Events and Objects

• Events are triggered by changes to objects
• Events carry object data
• Events enable tracking object lifecycle

Events and Schemas

• Schema changes trigger events
• Events can be used to validate schema compatibility
• Events enable schema evolution tracking

Events and Registers

• Register operations trigger events
• Events can be used to monitor register usage
• Events enable register lifecycle management

Events and Files

• File operations trigger events
• Events carry file metadata
• Events enable file processing workflows

Use Cases

1. Integration

Use events to integrate with other systems:

• Sync data with external systems
• Trigger notifications in messaging platforms
• Update search indexes

2. Workflow Automation

Build automated workflows:

• Generate documents when objects are created
• Send approval requests when objects are updated
• Archive data when objects are deleted

3. Audit and Compliance

Implement audit and compliance features:

• Log all changes to sensitive data
• Track who did what and when
• Generate compliance reports

4. Custom Business Logic

Implement custom business logic:

• Validate complex business rules
• Enforce data quality standards
• Implement approval workflows

Best Practices

1. Keep Listeners Focused: Each listener should have a single responsibility
2. Handle Errors Gracefully: Listeners should not break the system if they fail
3. Consider Performance: Heavy processing should be done asynchronously
4. Document Events: Clearly document what events are available and when they're triggered
5. Version Events: Consider versioning events to handle changes over time
6. Test Event Handling: Write tests for event listeners
7. Monitor Event Flow: Implement monitoring for event processing

Conclusion

Events in Open Register provide a powerful mechanism for extending functionality, integrating with other systems, and building loosely coupled architectures. By leveraging the event-driven approach, you can create flexible, scalable applications that can evolve over time while maintaining a clean separation of concerns.