HATEOAS - How to model link relations that change state

Question

Following HATEOAS principles that each states should be hyperlinked, what is the best way to model links that change resource state?

Let\'s take classical example wi

Answer 1

Modelling resources is the most difficult part of REST. Strictly adhering to the standard means if you see yourself ever doing this: /resource/:id/{action}, you're violating the "using HTTP correctly" criteria, as your endpoints should ideally always be "nouns', never "verbs" (the verbs are what the HTTP protocol provides).

So, while "it depends" (ie. the hard part of designing resources), typically: Object model states can be considered as resources themselves.

Which means, your order status is actually a resource you can query (either as a standalone /orderstatuses resource or as a sub resource eg. /orders/:id/status)

Your Application State can now link to the status resource based on the current status of the order itself. If your 'status' schema looks something like this (pseudo):

key: 'status'
values: ['pending', 'cancelled']

Your app could then PUT /order/:id/status {status:'cancelled'} (a well formed status) back to the API, which would then act to cancel your order. It's a little weird thinking in these terms (RPC is a lot more intuitive), but hopefully this helps.