Model Signals in ORMBridge

Overview

ORMBridge keeps your frontend and backend data in sync by using signals. This document explains how these signals work and best practices for using them.

How Signals Work in ORMBridge

Signals in ORMBridge serve two critical purposes:

1. Data Synchronization: Keeping frontend data in sync with backend changes
2. Cache Invalidation: Ensuring cached data is refreshed when models are modified

When you register a model with ORMBridge:

1. Standard Operations: Creating, updating, or deleting individual instances through Django triggers the standard Django signals (post_save and post_delete).

2. Bulk Operations: When performing bulk operations from the frontend, ORMBridge uses its own special signals (not Django signals) to ensure cache invalidation works properly.

# Triggers Django post_save signal
instance = MyModel.objects.create(name="Example")

# Triggers Django post_save signal
instance.name = "Updated"
instance.save()

# Triggers Django post_delete signal
instance.delete()

Important Considerations

Bypassing ORMBridge

If you perform bulk operations directly with Django's ORM (bypassing ORMBridge), no signals will be triggered:

# No signals triggered
MyModel.objects.filter(category="old").update(category="new")

# No signals triggered
MyModel.objects.filter(is_archived=True).delete()

This can cause your frontend to display outdated information.

Best Practices

To keep your data consistent:

1. Use the ORMBridge client for all operations when possible.

2. If you must use direct Django ORM (for performance with large datasets), manually trigger signals:

# For bulk updates:
affected_records = MyModel.objects.filter(category="old")
affected_ids = list(affected_records.values_list('id', flat=True))
affected_records.update(category="new")

# Manually trigger signals
from django.db.models.signals import post_save
for instance in MyModel.objects.filter(id__in=affected_ids):
    post_save.send(sender=MyModel, instance=instance, created=False)

3. For large datasets, consider:
   • Working in smaller batches
   • Using background tasks
   • Temporarily disabling signals and manually invalidating caches afterward

Summary

• ORMBridge uses Django signals for standard operations
• ORMBridge uses its own special signals for frontend bulk operations
• Both types of signals ensure proper data synchronization and cache invalidation
• Operations outside ORMBridge won't trigger any signals
• Always use ORMBridge when possible, or manually trigger signals when bypassing it