Receive Django signals for a model (workaround for bug in built-in sender filtering)

decorators.py

def model_instance_signal_receiver(signal, Model):
    """Register signal receiver for a specific model

    When using QuerySet.defer(), the model objects are instances of a subclass, so
    the built-in sender matching doesn't work. This approach uses that subclassing
    to ensure we run the receiver for both deferred and non-deferred instances.

    As a side effect, this also allows you to register a receiver for all
    subclasses of an abstract model.
    """
    from django.dispatch import receiver
    def decorator(fn):
        @receiver(signal)
        @wraps(fn)
        def wrapper(sender, **kwargs):
            if issubclass(sender, Model):
                instance = kwargs.pop('instance')
                if instance is not None:
                    kwargs['sender'] = sender
                    return fn(instance, **kwargs)
        return wrapper
    return decorator

Example usage:

@model_instance_signal_receiver(post_save, models.Trip)
def update_brief_stats(trip, **kwargs):
    if kwargs.get('created'):
        pass
    else:
        logger.info('Trip modified')