Editing waterpoints should invalidate cache

[kynan]

We're caching API requests client side (in particular waterpoints). However editing a Waterpoint does not invalidate this cache.

[kynan]

That's a tricky one, I'm out of ideas: the request for waterpoints is always served from browser cache, no matter what I try. For reasons I can't understand this is not the case for region_name and district_name.

[kynan]

An option might be to explicitly bust the cache using an additional bogus query parameter. This could be an int which is incremented whenever a waterpoint is updated client side. This would of course still not work if waterpoints change server side through another client.

Maybe we can cover both cases by sending a If-Modified-Since header. The question is which value to use (ideal would be the Last-Modified of whichever response is in cache) and how to achieve this using $resource.

[kynan]

Turns out $resource does send an If-Modified-Since header, however I can't figure out which timestamp it picks and can't find that documented anywhere.