RESTful API architecture: Queries over multiple resources

Question

I have PHP classes for each resource in a RESTful API. Depending on the request method it will be routed to call the right function. Here's an example for a GET call on the Users:

Class Users{
    public function get($params){
        // get information and return result
    }
}

Requesting all users would be /api/users/ . Requesting a single user /api/users/:id
So far no problems.

Now my question: When requesting something like this /api/users/:id/posts the API should return all posts made by the user with a specific id ( Posts is another resource btw)

How would I implement this call in the PHP Class structure given above?

Handle it with the parameters in the get() function in the resource Users ?
Add a new resource UsersPosts ?
Add a function in new method in the Users class?

Answer 1

You should create a Router class that determines which controller class and method is called on a request (check out the some established frameworks like Symfony or Kohana to see how they handle routing for ideas, or even use them!). From there, whether you do Users::getPosts($userId) or Posts:getByUserId($userId) is up to you (to me, a UsersPosts class indicates a cross-ref of some kind and may not be the best name for a controller or model).

Answer 2

It would be easier if you think of the 'user' as a filter to the posts resource than dealing with 2 different resources at the same time.

Something to look like this:

/api/posts/by_user/user_id

In this way you could keep only one resource per api page, and apply as many filters as you want.

/api/posts/by_user/USER_ID/category/videos/

Personally I go even further and have other criterias like order_by or order_dir in the url scheme, and they can all be appended to each other, and interchanged, like:

/api/posts/category/videos/by_user/USER_ID/order_by/title/order_dir/asc/limit/5