@danpalmer Django signals are a nice generic way of doing this - essentially we can write handlers which hook into various stages of the model lifecycle, e.g. handling updates to models before or after saving them.

See https://github.com/monzo/response/blob/master/response/slack/signals.py for some examples where we use this, e.g. to keep the Slack headline post updated when an incident's details change.

We can also define our own custom signals - this would be an easy way to achieve the @incident_closed annotation you've defined above. Actually, I think this would be a great idea, and a nicer interface for people to use rather than hooking directly into model update signals.

@milesbxf great idea, I hadn't considered signals. I agree that defining new signals would probably be a better idea here, the model change events might be tricky to decode exactly what's changing. I'll have a go at implementing this sometime. Will update here before I do though in case anyone else wants to take a look first.