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

Post a Comment

Popular posts from this blog

Finalization, Know What it Costs

This is a post about object finalization in .NET. Finalization is not as inexpensive as we think, it increases the pressure put on GC.All objects that need finalization are moved into a finalizable queue and the actual finalization happens in a separate thread. Because the objects full state may be needed, the object itself and all the object it points to are promoted to the next generation (this is needed so that GC does not clean these objects off in the current round), and these objects are cleaned up only after the following GC. Due to this reason, resources that need to be released should be wrapped in as small a finalizable object as possible, for instance if your class needs a reference to an unmanaged resource, then you should wrap the unmanaged resource in a separate finalizable class and make that a member of your class and furthermore the parent should be a non-finalizable class. This approach will assure that only the wrapped class (class that contains the unmanaged resourc...
1 comment
Read more

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 above When 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 implementa...
4 comments
Read more

The maximum nametable character count quota (16384) has been exceeded

Some of our services were growing and the other day it hit the quote, I could not update the service references, nor was I able to run the WCFTest client. An error is diplayed saying " The maximum nametable character count quota (16384) has been exceeded " The problem was with the mex endpoint, where the XML that was sent was too much for the client to handle, this can be fixed by do the following. Just paste the lines below within the configuration section of the devenve.exe.config and the svcutil.exe.config files found at the locations C:\Program Files\Microsoft Visual Studio 9.0\Common7\IDE , C:\Program Files\Microsoft SDKs\Windows\v6.0A\bin Restart IIS and you are done. The detailed error that you get is the following : Error: Cannot obtain Metadata from net.tcp://localhost:8731/ Services/SecurityManager/mex If this is a Windows (R) Communication Foundation service to which you have access, please check that you have enabled metadata publishing at the specified address. F...
5 comments
Read more