Monday, January 23, 2012

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.



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