Principle 4 : Communication are done by representation

When you send any request or you get any response, you are actually sending representations.

For example let's say you want to create a new customer record, you would send some kind of representation as shown below using HTTP PUT.

Once the resource is created you would get a representation as shown below. The below representation says the customer questpond has been successfully created and if you wish you can use "http://www.questpond.com/Customer/Questpond/Orders" defined in the "Next" tag to create orders for the "questpond" customer.

The above representation was in XML format if you wish you can also send and received other presentations like JSON. For instance below is a simple JSON snippet for creating a new customer record with name and address.

Principle 5 : Be Stateless

Every request should be an independent request so that we can scale up using load balancing techniques. Independent request means with the data also send the state of the request so that the server can carry forward the same from that level to the next level.

For instance below are two simple representations, the first representation is sent for logging in.

If you are logged in successfully you receive the below representation.

If you want to search for customer, you would send him the below representation stating that you are in a state of successful logging in and would like to search all customers.

In other words every request is independent and the server does not need to remember your previous request and states.

Summarizing 5 principles of REST

So summarizing REST leverages the old web HTTP by applying principles 5 important principles:-

• Everything is a resource.
• Every resource is identified by a unique identifier.
• Use simple and uniform interfaces.
• Communication are done by representation.
• Be Stateless.

Implementing REST with WCF services

Enabling WCF REST services is a three step process:-

• Enable HTTP bindings.
• Expose methods via common interfaces.
• Define your representation.

Create a new endpoint and bind the behavior with your end point.

In order to make your interfaces uniform you we can use the "UriTemplate" property as shown in the below figure. You can see from the below code snippet how "getStudents" can now be called by using a http GET request on "/Students/123" , where 123 is the id of the student.

In the same way in the below code snippet we are calling "AddStudent" method using HTTP POST and we have made the interface uniform using the "UriTemplate" property as shown in the below code snippet.

So now if you want to get a particular student use http://localhost:27683/Students.svc/Students/1 with HTTP GET method and if you want to add a new student call http://localhost:27683/Students.svc/Students/Shiv with HTTP POST. Is n't that much simple as compared to "getStudents" and "AddStudent" methods.

Below is the implemented code for the above interface. We have created a collection of student names in a string collection. In order to add new students we can call "AddStudent" and to retrieve students we can call "getStudents".

Testing the above WCF REST services using simple HTML form

To get a particular student we need to invoke "getStudents" by using HTTP GET on the URL http://localhost:27683/Students.svc/Students/1 . The "1" indicates that we want to retrieve the student with ID "1".

To add a particular student we need to invoke "Addstudent" by using HTTP POST on the URL http://localhost:27683/Students.svc/Students/Shiv . "Shiv" is the student name we wish to add to the collection.

In order to make a post and get on the above URL's we will use simple HTML to do the same. You can also use other methods like "xmlhttprequest" , WCF proxy etc. In order to keep it simple in this article we will use simple HTML for now.

So if you run the above HTML with the action pointing to the URL http://localhost:27683/Students.svc/Students/1 and using the "get" method you should get the below output.

In the same way if you run the below HTML with the action pointing to the URL (http://localhost:27683/Students.svc/Students/shiv ) and using the "post" method you should get the below output.

In the same way you can try for other HTTP methods like PUT , DELETE etc.

What about representations?

When we discussed REST fundamentals we said one of the most important things is representation and format of representation. The current WCF [WebGet] and [WebInvoke] attribute help you to configure formats in both request and response in XML and JSON format.

In the below code snippet we have created the Responseformat as JSON.

If you do a get on the URL you should get the value as shown in the below figure.

Video on REST

If not clear with the above concepts explained see our video on What is REST?

Do watch my 500 videos on C#, .NET, WCF, Design Patterns, SilverLight, SharePoint etc.