Skip to main content

WCF REST versioning, JSON and Dynamic objects

As everyone knows JSON is a very light weight form of transport when it comes to the web, you can respond and consume JSON using WCF REST services, I have blogged about this in one of my earlier posts in 2008, but last month I got to work on this...
WCF makes things very easy, if the client sends a JSON formatted string, WCF infrastructure will de-serialize this into a custom type that you have specified in your operation contract.
For an example...

[WebInvoke(Method="POST"....)]
public void Save(Student student){}


so if you send a JSON string like this on your POST body

{Name : "Nairooz Nilafdeen", Age : 26}
...the WCF infrastructure will de-serialize the JSON string into the Student object (as long as the JSON key-value matches the properties in the Student type)..

Now, the problem with this approach is when you send a JSON string that contains an additional property that is not available in the Student class, now WCF will not be able to de-serialize as the JSON string does no exactly match with the Student type.

In a few situation you want to keep one simplified API that users would want to access, but how do you take versioning into account?
The simplest way would be to except a stream into your operation, so now it becomes like this...


[WebInvoke(Method="POST"....)]
public void Save(Stream stream){}

(you can alternativley make 2 URLs available for differen versions...)
Now all the client needs to do is send any version of the Student type but also send the version of the service it's using in the header..on the service side you would look at the header and according to the version you will fill in the correct version of the Student type...
but, now the issue is that you are getting a JSON stream, now you need to read this and get the correct values for the stream...

Let .Net dynamic do the talking, you can use the DynamicJson library available at codeplex (google it...)and you can do this...

dynamic jsonObject = DynamicJson.Parse(stream);

you can access the Name property of the JSOn stream like this...

string name = jsonObject.Name;

and whats more interesting is when you are creating a unit test to test out this API...
simply create a ExpandoObject (another dynamic object) and just keep on filling what you need, no need to create a static class...

ExpandoObject obj = new ExpandoObject();
obj.Name = "Nairooz Nilafdeen";

I know the post is not really concise, but noting it down for my future use.



Comments

Popular posts from this blog

Hosting WCF services on IIS or Windows Services?

There came one of those questions from the client whether to use II7 hosting or windows service hosting for WCF services. I tried recollecting a few points and thought of writing it down.
WCF applications can be hosted in 2 main ways- In a Windows service- On IIS 7 and aboveWhen WCF was first released, IIS 6 did not support hosting WCF applications that support Non-HTTP communication like Net.TCP or Net.MSMQ and developers had to rely on hosting these services on Windows Services.With the release of IIS 7, it was possible to deploy these Non-Http based applications also on IIS 7. Following are the benefits of using IIS 7 to host WCF applications
Less development effort
Hosting on Windows service, mandates the creating of a Windows service installer project on windows service and writing code to instantiate the service, whereas the service could just be hosted on IIS by creating an application on IIS, no further development is needed, just the service implementation is n…

Task based Asynchronous pattern, Async & Await and .NET 4.5

One of the key features in .Net 4.5 is to write asynchronous programs much easier. So if I was to write asynchronous programs in .Net 2.0/3.5, I would either follow the event based model or the callback based model. For an example, a synchronous method that does intensive work (say the DoWork()) can be made asynchronous by using the following patterns
1) Implementing the IAsyncResult pattern. in this implementation, 2 methods are exposed for the DoWork() synchronous method, the BeginDoWork() and the EndDoWork() method. The user will call the BeingDoWork() passing in the required parameters and a callback of the delegate type AsyncCallback(IAsyncResult). The BeginDoWork() will spawn a new thread a return control back to the user. Once work is completed in the spawned method, as a last step, it will call the inform the AsyncResult implementation, which in turns will call the EndDoWork() (which is the callback that was passed in to the BeginDoWork()).
2) Implementing the event pattern. Her…

MEF (Managed Extensibility Framework), .NET 4, Dependency Injection and Plug-in Development

Almost after .Net 4 was released I remember reading about MEF (Managed Extensibility Framework), this was a framework for developers to compose their application with required dependencies. At first this looks like the Unity Container used for dependency injection, but MEF is much more than a dependency container but there is nothing stopping you from using MEF as a dependency injector.I remember around 5 years back when I was in a project that created a framework that allows developers to plug-in there modules as WinForm screens. The developer would create a set of screens with the intended functionalities and the drop this component in the bin folder of the framework and then will move on to do some painful configurations for the framework to pick up the module. Dropping the component into the bin folder and doing a bit of configuration is all that s needed for the framework to pick up display the screens. Typically, the configurations would also contain metadata about the screen.Al…