Question

I read the article at REST – complex applications and it answers some of my questions, but not all.

I am designing my first REST application and need to return “subset” lists to GET requests. Which of the following is more “RESTful”?

/patients;listType=appointments;date=2010-02-22;user_id=1234

or

/patients/appointments-list;date=2010-02-22;user_id=1234

or even

/appointments/2010-02-22/patients;user_id=1234

There will be about a dozen different lists that I need to return. In some of these, there will be several filtering parameters and I don’t want to have big ‘if’ statements in my server code to select the subsets based on which parameters are present. For example, I might need all patients for a specific doctor where the covering doctor is another and the primary doctor is yet another. I could select with

/patients;rounds=true;specific_id=xxxx;covering_id=yyyy;primary_id=zzzz

but that would require complicated branching logic to get the right list, where asking for a specific subset (rounds-list) will achieve that same thing.

Note that I need to use matrix parameters instead of query parameters because I need to do filtering at several levels of the URL. The framework I am using (RestEasy), fully supports matrix parameters.

Answer 1

Ralph,

the particular URI patterns are orthogonal to the question how RESTful your application will be.

What matters with regard to RESTfulness is that the client discovers how to construct the URIs at runtime. This can be achieved either with forms or URI templates. Both hypermedia controls tell the client what parameters can be used and where to put them in the URI.

For this to work RESTfully, client and server must know the possible parameters at design time. This is usually achieved by making them part of the specification of the link relationship.

You might for example define a ‘my-subset’ link relation to have the meaning of linking to subsets of collections and with it you would define the following parameters:

listType, date, userID.

In a link template that spec could be used as

<link rel=”my-subset’ template=”/{listType}/{date}/patients;user_id={userID}”/>

Note how the actual parameter name in the URI is decoupled from the specified parameter name. The value for userID is late-bound to the URI parameter user_id.

This makes it possible for the URI parameter name to change without affecting the client.

You can look at OpenSearch description documents (http://www.opensearch.org) to see how this is done in practice.

Actually, you should be able to leverage OpenSearch quite a bit for your use case. Especially the ability to predefine queries would allow you to describe particular subsets in your ‘forms’.

But see for yourself and then ask back again 🙂

Jan