Why isn't HTTP PUT allowed to do partial updates in a REST API?

Question

Who says RESTful APIs must support partial updates separately via HTTP PATCH?

It seems to have no benefits. It adds more work to implement on the server side and mor

Answer 1

Who says? The guy who invented REST says:

@mnot Oy, yes, PATCH was something I created for the initial HTTP/1.1 proposal because partial PUT is never RESTful. ;-)

https://twitter.com/fielding/status/275471320685367296

First of all, REST is an architectural style, and one of its principles is to leverage on the standardized behavior of the protocol underlying it, so if you want to implement a RESTful API over HTTP, you have to follow HTTP strictly for it to be RESTful. You're free to not do so if you think it's not adequate for your needs, nobody will curse you for that, but then you're not doing REST. You'll have to document where and how you deviate from the standard, creating a strong coupling between client and server implementations, and the whole point of using REST is precisely to avoid that and focus on your media types.

So, based on RFC 7231, PUT should be used only for complete replacement of a representation, in an idempotent operation. PATCH should be used for partial updates, that aren't required to be idempotent, but it's a good to make them idempotent by requiring a precondition or validating the current state before applying the diff. If you need to do non-idempotent updates, partial or not, use POST. Simple. Everyone using your API who knows how PUT and PATCH works expects them to work that way, and you don't have to document or explain what the methods should do for a given resource. You're free to make PUT act in any other way you see fit, but then you'll have to document that for your clients, and you'll have to find another buzzword for your API, because that's not RESTful.

Keep in mind that REST is an architectural style focused on long term evolution of your API. To do it right will add more work now, but will make changes easier and less traumatic later. That doesn't mean REST is adequate for everything and everyone. If your focus is the ease of implementation and short term usage, just use the methods as you want. You can do everything through POST if you don't want to bother about clients choosing the right methods.