Q:

REST API - Update of single resource changes multiple others

I'm looking for a way how to deal with a following problem:
Imagine you modify a resource and that subsequently causes update of other resources.
E.g. you issue a PUT to, say /api/orders/1234, which by definition changes state of all other Orders of given user. There may be UI clients that display the table of Orders and they should know that not only single item in the table was updated, but eventually other as well.
Now, is there any standard way how inform a clients about such a situation?
So far I can only think of sending back the 205 Reset Content HTTP status code to inform the client that he should refresh the state, as not just a single thing was changed.

A:

There are multiple solutions. 

You can define specific resources as non-cacheable, so the client does not cache them at all. (no-store)
You can try giving a max-age of 0, so the client will have to re-validate those resources always. In this case you might have to implement ETags and conditional GETs, but it will be easier on the server than option 1.
Some push method like WebSockets.

If you really want to "notify" potentially multiple clients of a change, then it sounds like you would need option 3.
However, correctly configured caching is normally good enough. For example you could mark not-yet-executed orders as not cached (max-age=0), but as soon as it is executed, you might mark it to be cached indefinitely, since it can not change anymore.

