Handling self-joins in a RESTful endpoint

In my previous post, I set up a sample scenario where you can programmatically look up a user's customers or vendors using a many-to-many self-join relational schema. The logical next step is to provide a way for external users to filter and access this data from a user-facing application.

If you're using Rails as your platform to expose a RESTful API, those URL resource endpoints generally reflect object models that map to a corresponding database table. And it's common practice to refer to child resources as part of a parent resource's path (e.g. /author/id/books ie access all the books for a given author). In this scenario, our child resource does not reflect an actual object model (e.g. /user/id/customers). We don't have an actual customer or vendor table; both resources would refer back to the User model.

Add new Member Routes

The first thing to do is to add new member routes to your routes.rb file. For us, we would add customers and vendors member routes to the users collection route:

Defining a member routes in a parent collection.

This definition recognizes a GET request to, say, /users/1/customers and it maps this route to the UsersController#customers action in the Users controller. The Users resource ID value is passed in params[:id].

Add a new Action

We'll need to add a new action for each of the member routes. For brevity, we'll only define the customers action; making the vendors action will be left as an exercise for the reader. In brief, the code used in the previous blog post illustrating how to access the model is used for the action definition.

Defining a new action in the User controller.

As part of the action definition, a user can include an optional is_premier_customer parameter in the GET request (e.g. /users/1/customers?is_premier_customer=true).

Add a new template

For the final step, we need to add a new template file to handle the new action. For this example, we're going to make a template file that's parsed by jBuilder template engine to generate JSON data. (jBuilder is used by default if you tell the Rails 5 application generator to set up a RESTful API application.)

We'll make a new file called customers.json.jbuilder defined with the following line: