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# Signals
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Django signal system integration for reacting to preference changes. The signals module provides Django signals that are emitted when preferences are updated, allowing you to hook into preference changes for custom logic, logging, or cache invalidation.
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## Capabilities
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### Preference Updated Signal
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Signal emitted whenever a preference value is updated through any mechanism (manager, admin, API, forms). This signal is sent after the preference value has been successfully changed in the database.
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```python { .api }
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from django.dispatch import Signal
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preference_updated: Signal
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```
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**Signal Arguments:**
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- `sender`: The preference class that was updated
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- `section`: Section name of the updated preference
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- `name`: Name of the updated preference  
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- `old_value`: Previous value of the preference
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- `new_value`: New value of the preference
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- `instance`: The preference model instance that was updated
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### Usage Examples
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**Connecting to the Signal:**
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```python
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from dynamic_preferences.signals import preference_updated
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from django.dispatch import receiver
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@receiver(preference_updated)
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def handle_preference_change(sender, section, name, old_value, new_value, instance, **kwargs):
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    """Handle preference updates for logging or cache invalidation."""
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    print(f"Preference {section}__{name} changed from {old_value} to {new_value}")
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    # Example: Clear cache when maintenance mode changes
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    if section == 'general' and name == 'maintenance_mode':
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        from django.core.cache import cache
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        cache.clear()
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# Alternative connection method
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def notify_on_preference_update(sender, section, name, old_value, new_value, instance, **kwargs):
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    """Send notification when important preferences change."""
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    if section in ['email', 'notifications']:
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        # Send notification to administrators
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        pass
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preference_updated.connect(notify_on_preference_update)
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```
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**Using in Django Apps:**
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```python
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# apps.py
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from django.apps import AppConfig
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from dynamic_preferences.signals import preference_updated
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class MyAppConfig(AppConfig):
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    default_auto_field = 'django.db.models.BigAutoField'
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    name = 'myapp'
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    def ready(self):
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        preference_updated.connect(self.handle_preference_update)
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    def handle_preference_update(self, sender, section, name, old_value, new_value, instance, **kwargs):
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        # Custom handling logic
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        pass
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```
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**Filtering by Preference Type:**
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```python
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@receiver(preference_updated)
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def handle_site_preferences(sender, section, name, old_value, new_value, instance, **kwargs):
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    """Only handle site-wide configuration changes."""
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    if section == 'site_config':
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        # Rebuild static files, clear CDN cache, etc.
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        pass
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```
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The signal is automatically emitted when preferences are updated through:
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- PreferencesManager (programmatic updates)
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- Django Admin interface
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- REST API endpoints
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- Form submissions