How to implement HATEOAS in Rails

Question

I've started with ActiveResource, but quickly hit the wall. Could not get ActiveResource to work when overriding to_json and to_xml on the underlying model. Plus, could not make resource representation inject links into the generated xml document. Oh btw, I'm using Rails 3.2.1.

I did a bit of research and found out about its gem. Tried it, for some reason didn't work for me. So my question is:

If I have one resource (say books) hosted in one web site (something like http://books.org), and another resource (say students, http://students.org), hosted in another web site, how can I get books to represent themselves to a student in their full HATEOS glory?

I was able to get the book resource to represent itself to the asking student as an XML document. I did that by using vanilla Rails ActiveResource in the students site. I've created Books resource that inherits from ActiveResource::Base. Then I specified the self.site and self.element_name, after which I was able to perform some rudimentary ActiveRecord-like queries against the remote books site. The only thing that worked for me was Book.all and Book.find(1). Even that was not satisfactory because the representation contained all database columns, and I wanted to at least remove some of those, which turned out not to be possible.

Now that I've abandoned that approach, I am wondering if there is a working example in Rails where it is possible to build a more sophisticated representation of a resource (i.e. books) that will contain links that will drive the application state transfer? I find it simply unbelievable that such a simple requirement seems so devilishly difficult to implement in Rails. All I'm trying to do is create a representation of a resource that will include some links which will guide the consumer on its discovery of what that resource is capable of. I'm mostly interested in implementing the workflow, which is a layered, peeling-the-onion type of conversational process of discovery.

Answer 1

In Rails, you'd need to change the way the serialization of your object happens if you're looking to do this in JSON. (You need to override the way Rails gives back representations of resources.) The most common gem for doing that would be: https://github.com/rails-api/active_model_serializers

If you don't want to use AMS or want to return HTML, consider following this presenter pattern: http://blog.steveklabnik.com/posts/2012-01-06-implementing-hateoas-with-presenters