Options for the RESTFul approach for follow and unfollowing

Question

I'm looking at implementing a new RESTFul call where a User can follow/unfollow a generic 'thing' item, but I need to know the best or common approach below, 1 or 2?

1) A GET or POST on the following URL's:

user/{thing_to_follow_id)/follow
user/{thing_to_follow_id)/unfollow

Or

2) A POST containing thing_to_follow_id

POST
user/follow

A DELETE on

user/follow/{thing_to_follow_id}

The first seems the most restful, but it feels wrong to post an empty payload where the second allow me to do a GET and return all things a user is following.

What is the best approach here?

Answer 1

Per the HTTP spec, GET calls should be safe - that is,

the client does not request, and does not expect, any state change on the origin server as a result of applying a safe method to a target resource

Furthermore, one of the principles of REST is that URIs point to things (nouns), rather than to actions (verbs). In your case, the user would have a collection of things that they follow. That might look more like:

add a new thing to the collection of things the user follows
POST /user/follows 
{
    thing
}

get all the things the user follows
GET /user/follows

stop following a thing
DELETE /user/follows/{id}

Another option would be to use a mapping resource, such as:

add a new thing to the collection of things the user follows
POST /user-follows
{
    user
    thing
 }

 get all the things the user follows
 GET /user-follows?userId={id}

 get all the users following a thing
 GET /user-follows?thingId={id}

 stop following a thing
 DELETE /user-follows/{id}
 DELETE /user-follows?thingId={id}&userId={id}

Answer 2

You can think of the mapping between a user and a thing to follow as a unique resource in of itself, which can have two different states, either true or false depending on whether the user is following the thing in question.

So a way of doing this would be for the client to PUT a new state of that resource on the server, since the client should already know the location of the resource. Your URL schema could be something like

/users/<user_id>/things/<thing_id>

or something similar that conveys that this is a resource representing the state of mapping between user and thing.

A GET on this resource would tell you if User A is following Thing B

Request
  GET /users/<user_id>/things/<thing_id>

Response
  200 OK
  {following: true}

And the client can change that state by PUTing a new state

Request
  PUT  /users/<user_id>/things/<thing_id>

  {following: false}

Response
  204 No Content

Answer 3

As you are basically updating/creating some line in some table when a user decides to follow or unfollow an item, you shouldn't be using GET.

Rather user POST or PUT

POST or PUT:
user/{thing_to_follow_id)/follow

PUT:
user/{thing_to_follow_id)/unfollow

And unless you are actually deleting something (if someone else can later choose to follow that item) then don't use a DELETE.