Web API versioning using querystring parameter

Veröffentlicht am: 28 Februar 2017
auf dem Kanal: kudvenkat

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In this video we will discuss versioning a Web Service using a QueryString parameter.

Before we implement versioning using a querystring parameter. First let's understand how a controller is selected when a request is issued to a web api service. For example, let us understand how a controller is selected when a rquest is issued to the following URI
/api/students/1

In Web API, there is a class called DefaultHttpControllerSelector. This class has a method called SelectController() that selects the controller based on the information it has in the URI.

In the URI we have
1. The name of the controller, in this case students
2. The id parameter value, in this case 1

So from the URI, the SelectController() method takes the name of the controller in this case "Students" and finds "StudentsController" and returns it. This is the default implementation that we get out of the box.

This default implementation will not work for us because, in our service we do not have controller that is named StudentsController. Instead we have
1. StudentsV1Controller and
2. StudentsV2Controller

When a request is issued to the following URI, depending on the query string parameter "v" value we want to select the controller. If the value is 1, select StudentsV1Controller, and if it is 2, then select StudentsV2Controller.
/api/students?v=1

Step 1 : Since the default controller selector implementation provided by Web API does not work for us, we have to provide our own custom controller selector implementation. To do this
1. Add a folder to the web api project. Name it "Custom"
2. Add a class file to the folder. Name it "CustomControllerSelector".

For the "CustomControllerSelector" class code please check the link below
http://csharp-video-tutorials.blogspo...

Step 2 : The next thing that we need to do is, replace the default controller selector with our custom controller selector. This is done in WebApiConfig.cs file. Notice we are replacing IHttpControllerSelector, with our CustomControllerSelector. DefaultHttpControllerSelector implements IHttpControllerSelector, so that is the reason we replacing IHttpControllerSelector.

config.Services.Replace(typeof(IHttpControllerSelector),
new CustomControllerSelector(config));

Step 3 : Include the following default route in WebApiConfig.cs

config.Routes.MapHttpRoute(
name: "DefaultRoute",
routeTemplate: "api/{controller}/{id}",
defaults: new { id = RouteParameter.Optional }
);

Step 4 : Remove [Route] attribute, from action methods in StudentsV1Controller and StudentsV2Controller

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