One of the annoyances of HTTP is that it is not really possible to make complex queries easily. To be rather more exact, you can make a complex query fairly easily, but at some point you’ll reach the URI limit, and worse, there is no easy way to make multiple queries in a single round trip.

I have been thinking about this a lot lately, because it is a stumbling block for a feature that is near and dear to my heart, the Future Queries feature that is so useful when using NHibernate.

The problem was that I couldn’t think of a good way of doing this. Well, I could think of how to do this quite easily, to be truthful. I just couldn’t think of a good way to make this work nicely with the other features of RavenDB.

In particular, it was hard to figure out how to deal with caching. One of the really nice things about RavenDB’s RESTful nature is that caching is about as easy as it can be. But since we need to tunnel requests through another medium for it to work, I couldn’t figure out how to make this work in a nice fashion. And then I remembered that REST didn’t actually have anything to do with HTTP itself, you can do REST on top of any transport protocol.

Let us look at how requests are handled in RavenDB over the wire:

GET http://localhost:8080/docs/bobs_address

HTTP/1.1 200 OK

{
  "FirstName": "Bob",
  "LastName": "Smith",
  "Address": "5 Elm St."
}

GET http://localhost:8080/docs/users/ayende

HTTP/1.1 404 Not Found

As you can see, we have 2 request / reply calls.

What we did in order to make RavenDB support multiple requests in a single round trip is to build on top of this exact nature using:

POST http://localhost:8080/multi_get

[
   { "Url": "http://localhsot:8080/docs/bobs_address", "Headers": {} },
   { "Url": "http://localhsot:8080/docs/users/ayende", "Headers": {} },
]

HTTP/1.1 200 OK

[
  { "Status": 200, "Result": { "FirstName": "Bob", "LastName": "Smith", "Address": "5 Elm St." }},
  { "Status": 404 "Result": null },
]

Using this approach, we can handle multiple requests in a single round trip.

You might not be surprised to learn that it was actually very easy to do, we just needed to add an endpoint and have a way of executing the request pipeline internally. All very easy.

The really hard part was with the client, but I’ll touch on that in my next post.