How do I use Django signals with an abstract model?

Question

I have an abstract model that keeps an on-disk cache. When I delete the model, I need it to delete the cache. I want this to happen for every derived model as well.

If I connect the signal specifying the abstract model, this does not propagate to the derived models:

pre_delete.connect(clear_cache, sender=MyAbstractModel, weak=False)

If I try to connect the signal in an init, where I can get the derived class name, it works, but I'm afraid it will attempt to clear the cache as many times as I've initialized a derived model, not just once.

Where should I connect the signal?

Answer 1

Create a custom manager for your model. In its contribute_to_classmethod, have it set a signal for class_prepared. This signal calls a function which binds more signals to the model.

Answer 2

I think you can connect to post_delete without specifying sender, and then check if actual sender is in list of model classes. Something like:

def my_handler(sender, **kwargs):
    if sender.__class__ in get_models(someapp.models):
        ...

Obviously you'll need more sophisticated checking etc, but you get the idea.