RESTful API中的向后兼容性

Question

I am currently designing an RESTful API implemented using the ASP.NET Web API.
One very important point is backward compatibility.
I would like to keep the actual API code free of any thoughts about backward compatibility, to ensure clean and up-to-date design.
I thought about solving this by having a layer of version translators.
Each of these translators knows how to transform the requests and responses of one specific version (vPrevious) into those of another specific version (vCurrent).
These translators could easily be stacked to ensure backward compatibility with an arbitrary number of old versions.
Each of these translators would be responsible for doing all kinds of stuff, like setting default values for new properties or even performing an array of different operations.

I thought about implementing a DelegatingHandler that examines the version number of the API the client wants to use and based on that knows which translators to use.
However, I fail to see how I would actually go about implementing this. As I see it, each translator actually needs to be a full blown ASP.NET Web API of its own, along with a routing table and controllers. That actually would be acceptable, but how would that translator controller route the data to the next one in the chain?

Answer 1

I think that the cleanest way is to keep each version you need to support, running. That means that each version has its own branch in your VCS and is focused on serving clients that is using that specific version. Code is clean and focused on one version. If you need to work against common components/databases etc, I think that you should implement that layer further down in your architecture, not in the REST API layer. This versioning layer should be the first layer, behind the REST API.

If it really does not work, I would probably design it so that the latest API is the only API that works against your real backend. The other versions simply call the other versions through a regular HTTP request... the older versions are REST clients of the newer API's. This is not super fast but the design is very clean and it is easy to understand where versioning code goes. If you have many clients that work against old API verisons, this might cause the solution to be too slow and you need to find more effective ways of doing it, but then, we are almost back to the first solution.