How do I update a web API resource by request while also reacting with backend?

Question

How do you update (RESTful) resources in a web API from the client, when you also need the backend to take actions regarding these changes?

Let's say I have a RESTful web API with the following resources:

• Worker - id, first_name, last_name, ...
• Project - id, title, due_date, ..., worker [ref to Worker]. A project can exist only if it belongs to a worker.

In the client (which is typically a mobile app), users can retrieve a list of some worker's projects. They can then modify each project in that list (update), delete, or create new ones. Changes must take place locally on the client side, until a "send" command is dispatched, only then the server should receive the updates. Kind of like a classic form use case.

The tricky part: I need the backend to take actions according to each change, both individually and also as a whole. For example:

1. A user retrieved some worker's projects list, deleted a project, and also updated the due_date of another.
2. According to this change, the backend needs to both send push notifications to all of that project's members, and also recalculate the relevant worker's priorities according the total change in their projects (one was deleted, another got postponed...).

How do I achieve this in the best way?

• If I update/delete/create each project by itself (with seperate POSTs, PUTs and DELETEs), when will the backend do the overall recalculation task?
• If I update them all together as a bulk (with PUT), the backend will then need to understand what exactly changed (which got deleted, which modified...), which is a hard chore.
• Another option I heard is to create a third utility resource, that's something like "WorkerProjectUpdater" that holds the changes that need to be made, like transactions, and then have a "daemon" going through it and actually committing the changes. This is also hard to achieve as in the real story there are many many types of modifications, and it'll be quite complex to create a resource (with a model and DB records) for every type of change.

I'm using Django with Django Rest Framework for that web service.

Appreciate your help!