How to version REST URIs

Question

What is the best way to version REST URIs? Currently we have a version # in the URI itself, ie.

http://example.com/users/v4/1234/ 

for version 4 of this representation.

Does the version belong in the queryString? ie.

http://example.com/users/1234?version=4 

Or is versioning best accomplished another way?

Answer 1

Do not version URLs, because ...

• you break permalinks
• The url changes will spread like a disease through your interface. What do you do with representations that have not changed but point to the representation that has? If you change the url, you break old clients. If you leave the url, your new clients may not work.
• Versioning media types is a much more flexible solution.

Assuming that your resource is returning some variant of application/vnd.yourcompany.user+xml all you need to do is create support for a new application/vnd.yourcompany.userV2+xml media type and through the magic of content negotiation your v1 and v2 clients can co-exist peacefully.

In a RESTful interface, the closest thing you have to a contract is the definition of the media-types that are exchanged between the client and the server.

The URLs that the client uses to interact with the server should be provided by the server embedded in previously retrieved representations. The only URL that needs to be known by the client is the root URL of the interface. Adding version numbers to urls only has value if you construct urls on the client, which you are not suppose to do with a RESTful interface.

If you need to make a change to your media-types that will break your existing clients then create a new one and leave your urls alone!

And for those readers currently saying that this makes no sense if I am using application/xml and application/json as media-types. How are we supposed to version those? You're not. Those media-types are pretty much useless to a RESTful interface unless you parse them using code-download, at which point versioning is a moot point.