ServiceStack: RESTful Resource Versioning

Question

I\'ve taken a read to the Advantages of message based web services article and am wondering if there is there a recommended style/practice to versioning Restful resources i

Answer 1

I am also trying to come with a solution for this and was thinking of doing something like the below. (Based on a lot of Googlling and StackOverflow querying so this is built on the shoulders of many others.)

First up, I don’t want to debate if the version should be in the URI or Request Header. There are pros/cons for both approaches so I think each of us need to use what meets our requirements best.

This is about how to design/architecture the Java Message Objects and the Resource Implementation classes.

So let’s get to it.

I would approach this in two steps. Minor Changes (e.g. 1.0 to 1.1) and Major Changes (e.g 1.1 to 2.0)

Approach for minor changes

So let’s say we go by the same example classes used by @mythz

Initially we have

class Foo {   string Name; }

We provide access to this resource as /V1.0/fooresource/{id}

In my use case, I use JAX-RS,

@Path("/{versionid}/fooresource")
public class FooResource {

    @GET
    @Path( "/{id}" )
    public Foo getFoo (@PathParam("versionid") String versionid, (@PathParam("id") String fooId) 
    {
      Foo foo = new Foo();
     //setters, load data from persistence, handle business logic etc                   
     Return foo;
    }
}

Now let’s say we add 2 additional properties to Foo.

class Foo { 
    string Name;   
    string DisplayName;   
    int Age; 
}

What I do at this point is annotate the properties with a @Version annotation

class Foo { 
    @Version(“V1.0")string Name;   
    @Version(“V1.1")string DisplayName;   
    @Version(“V1.1")int Age; 
}

Then I have a response filter that will based on the requested version, return back to the user only the properties that match that version. Note that for convenience, if there are properties that should be returned for all versions, then you just don’t annotate it and the filter will return it irrespective of the requested version

This is sort of like a mediation layer. What I have explained is a simplistic version and it can get very complicated but hope you get the idea.

Approach for Major Version

Now this can get quite complicated when there is a lot of changes been done from one version to another. That is when we need to move to 2nd option.

Option 2 is essentially to branch off the codebase and then do the changes on that code base and host both versions on different contexts. At this point we might have to refactor the code base a bit to remove version mediation complexity introduced in Approach one (i.e. make the code cleaner) This might mainly be in the filters.

Note that this is just want I am thinking and haven’t implemented it as yet and wonder if this is a good idea.

Also I was wondering if there are good mediation engines/ESB’s that could do this type of transformation without having to use filters but haven’t seen any that is as simple as using a filter. Maybe I haven’t searched enough.

Interested in knowing thoughts of others and if this solution will address the original question.

Answer 2

Try to evolve (not re-implement) existing services

For versioning, you are going to be in for a world of hurt if you try to maintain different static types for different version endpoints. We initially started down this route but as soon as you start to support your first version the development effort to maintain multiple versions of the same service explodes as you will need to either maintain manual mapping of different types which easily leaks out into having to maintain multiple parallel implementations, each coupled to a different versions type - a massive violation of DRY. This is less of an issue for dynamic languages where the same models can easily be re-used by different versions.

Take advantage of built-in versioning in serializers

My recommendation is not to explicitly version but take advantage of the versioning capabilities inside the serialization formats.

E.g: you generally don't need to worry about versioning with JSON clients as the versioning capabilities of the JSON and JSV Serializers are much more resilient.

Enhance your existing services defensively

With XML and DataContract's you can freely add and remove fields without making a breaking change. If you add IExtensibleDataObject to your response DTO's you also have a potential to access data that's not defined on the DTO. My approach to versioning is to program defensively so not to introduce a breaking change, you can verify this is the case with Integration tests using old DTOs. Here are some tips I follow:

• Never change the type of an existing property - If you need it to be a different type add another property and use the old/existing one to determine the version
• Program defensively realize what properties don't exist with older clients so don't make them mandatory.
• Keep a single global namespace (only relevant for XML/SOAP endpoints)

I do this by using the [assembly] attribute in the AssemblyInfo.cs of each of your DTO projects:

[assembly: ContractNamespace("http://schemas.servicestack.net/types", 
    ClrNamespace = "MyServiceModel.DtoTypes")]

The assembly attribute saves you from manually specifying explicit namespaces on each DTO, i.e:

namespace MyServiceModel.DtoTypes {
    [DataContract(Namespace="http://schemas.servicestack.net/types")]
    public class Foo { .. }
}

If you want to use a different XML namespace than the default above you need to register it with:

SetConfig(new EndpointHostConfig {
    WsdlServiceNamespace = "http://schemas.my.org/types"
});

Embedding Versioning in DTOs

Most of the time, if you program defensively and evolve your services gracefully you wont need to know exactly what version a specific client is using as you can infer it from the data that is populated. But in the rare cases your services needs to tweak the behavior based on the specific version of the client, you can embed version information in your DTOs.

With the first release of your DTOs you publish, you can happily create them without any thought of versioning.

class Foo {
  string Name;
}

But maybe for some reason the Form/UI was changed and you no longer wanted the Client to use the ambiguous Name variable and you also wanted to track the specific version the client was using:

class Foo {
  Foo() {
     Version = 1;
  }
  int Version;
  string Name;
  string DisplayName;
  int Age;
}

Later it was discussed in a Team meeting, DisplayName wasn't good enough and you should split them out into different fields:

class Foo {
  Foo() {
     Version = 2;
  }
  int Version;
  string Name;
  string DisplayName;
  string FirstName;
  string LastName;  
  DateTime? DateOfBirth;
}

So the current state is that you have 3 different client versions out, with existing calls that look like:

v1 Release:

client.Post(new Foo { Name = "Foo Bar" });

v2 Release:

client.Post(new Foo { Name="Bar", DisplayName="Foo Bar", Age=18 });

v3 Release:

client.Post(new Foo { FirstName = "Foo", LastName = "Bar", 
   DateOfBirth = new DateTime(1994, 01, 01) });

You can continue to handle these different versions in the same implementation (which will be using the latest v3 version of the DTOs) e.g:

class FooService : Service {

    public object Post(Foo request) {
        //v1: 
        request.Version == 0 
        request.Name == "Foo"
        request.DisplayName == null
        request.Age = 0
        request.DateOfBirth = null

        //v2:
        request.Version == 2
        request.Name == null
        request.DisplayName == "Foo Bar"
        request.Age = 18
        request.DateOfBirth = null

        //v3:
        request.Version == 3
        request.Name == null
        request.DisplayName == null
        request.FirstName == "Foo"
        request.LastName == "Bar"
        request.Age = 0
        request.DateOfBirth = new DateTime(1994, 01, 01)
    }
}

Answer 3

Framing the Problem

The API is the part of your system that exposes its expression. It defines the concepts and the semantics of communicating in your domain. The problem comes when you want to change what can be expressed or how it can be expressed.

There can be differences in both the method of expression and what is being expressed. The first problem tends to be differences in tokens (first and last name instead of name). The second problem is expressing different things (the ability to rename oneself).

A long-term versioning solution will need to solve both of these challenges.

Evolving an API

Evolving a service by changing the resource types is a type of implicit versioning. It uses the construction of the object to determine behavior. Its works best when there are only minor changes to the method of expression (like the names). It does not work well for more complex changes to the method of expression or changes to the change of expressiveness. Code tends to be scatter throughout.

Specific Versioning

When changes become more complex it is important to keep the logic for each version separate. Even in mythz example, he segregated the code for each version. However, the code is still mixed together in the same methods. It is very easy for code for the different versions to start collapsing on each other and it is likely to spread out. Getting rid of support for a previous version can be difficult.

Additionally, you will need to keep your old code in sync to any changes in its dependencies. If a database changes, the code supporting the old model will also need to change.

A Better Way

The best way I've found is to tackle the expression problem directly. Each time a new version of the API is released, it will be implemented on top of the new layer. This is generally easy because changes are small.

It really shines in two ways: first all the code to handle the mapping is in one spot so it is easy to understand or remove later and second it doesn't require maintenance as new APIs are developed (the Russian doll model).

The problem is when the new API is less expressive than the old API. This is a problem that will need to be solved no matter what the solution is for keeping the old version around. It just becomes clear that there is a problem and what the solution for that problem is.

The example from mythz's example in this style is:

namespace APIv3 {
    class FooService : RestServiceBase<Foo> {
        public object OnPost(Foo request) {
            var data = repository.getData()
            request.FirstName == data.firstName
            request.LastName == data.lastName
            request.DateOfBirth = data.dateOfBirth
        }
    }
}
namespace APIv2 {
    class FooService : RestServiceBase<Foo> {
        public object OnPost(Foo request) {
            var v3Request = APIv3.FooService.OnPost(request)
            request.DisplayName == v3Request.FirstName + " " + v3Request.LastName
            request.Age = (new DateTime() - v3Request.DateOfBirth).years
        }
    }
}
namespace APIv1 {
    class FooService : RestServiceBase<Foo> {
        public object OnPost(Foo request) {
            var v2Request = APIv2.FooService.OnPost(request)
            request.Name == v2Request.DisplayName
        }
    }
}

Each exposed object is clear. The same mapping code still needs to be written in both styles, but in the separated style, only the mapping relevant to a type needs to be written. There is no need to explicitly map code that doesn't apply (which is just another potential source of error). The dependency of previous APIs is static when you add future APIs or change the dependency of the API layer. For example, if the data source changes then only the most recent API (version 3) needs to change in this style. In the combined style, you would need to code the changes for each of the APIs supported.

One concern in the comments was the addition of types to the code base. This is not a problem because these types are exposed externally. Providing the types explicitly in the code base makes them easy to discover and isolate in testing. It is much better for maintainability to be clear. Another benefit is that this method does not produce additional logic, but only adds additional types.