Question

I have several models that save log data to my database. I also have a “recent events” app and I would like to choose which models send data to the events app. I thought a decorator would be good for this, so I could just add it to the models I want:

@logger
class TemperatureLog(models.Model):
    Date = models.DateTimeField(auto_now_add=True)
    Device = models.ForeignKey(TemperatureDevice)
    Data = models.PositiveIntegerField()

Here is the events model, Im using generic foreign keys:

class Event(models.Model):
    Active = models.BooleanField()
    Queue = models.BooleanField()
    ContentType = models.ForeignKey(ContentType)
    ObjectID = models.PositiveIntegerField()
    Event = generic.GenericForeignKey('ContentType', 'ObjectID')

And here is the decorator:

def logger(event):
    def wrap(*args, **kwargs):
        from toolbox.event.models import Event
        event(*args, **kwargs).save()
        myid = event(*args, **kwargs).id
        new = Event(Event=event.objects.get(id=myid))

        if Event.objects.all().filter(Active=True).count() >= 25:
            new.Queue = True
            new.save()

        else:
            new.Active = True
            new.save()

            for item in Event.objects.all().filter(Queue=True):
                item.Queue = False
                item.Active = True
                item.save()

                if  Event.objects.all().filter(Active=True).count() >= 25:
                    break
        return event(*args, **kwargs)

    return wrap

It works as it should, it creates the event instance and saves it. The problem that I have is that save() would be called twice. One in the decorator and the second in the actual code that collects the temperature logs (since I wont know ahead of time which apps will send events and which wont or if they might change in the future). So I wonder if there is a more elegant way to do this. I like the decorator approach since all I have to do is add it to the model class, but I am not very convinced of having save being called twice.

Answer 1

How about using post_save signal for all models

def log_saved_event(sender, instance, signal, *args, **kwargs):
    # handle Event class
    pass

from django.db.models import signals
from django.db import models

for m in models.get_models():
    signals.post_save.connect(log_saved_event, sender=m)