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ASP.NET Core Web API Versioning


Introduction:

An iteration and evolutionary changes of an ASP.NET Core Web API is handled by Versioning. Versioning of an API gives confidence to the clients which consumes API for a long time. Any changes or development of an API will be accessible using the new version and it won't cause issues to the clients consuming the old version of API.

When To Use Versioning:

  • Any API response changes.
  • Developing an API by implementing testing levels like 'Alpha', 'Beta', and 'RC' versions before releasing Production.
  • Deprecating an API which means API going to be removed or upgraded by a version within a short period.

Versioning Types:

  • Query String Versioning
  • Url Path Versioning
  • Media Type Versioning

API Version Nuget:

To Configure versioning to AspNet Core Web API Microsoft provided a library(Microsoft.AspNetCore.Mvc.Versioning). So to use the versioning library please install NuGet below.

            Install-Package Microsoft.AspNetCore.Mvc.Versioning -version 4.0.0

Register API Versioning:

Let's get started hands-on API Versioning, create the ASP.NET Core Web API project and install versioning NuGet package mentioned above. The primary step to get started with the version need to register the versioning service in the startup of our application. To do that go to  'Startup.cs' and configure versioning service as below.

public void ConfigureServices(IServiceCollection services)
{
 services.AddControllers();
 services.AddApiVersioning();
}

Register ApiVersion Attribute On A Controller:

'ApiVersion' is an attribute that takes a version number as an input parameter. Register this attribute on top of the controller to label the version to that endpoint. We can Register multiple versions on top of the controller and need to map the version to a specific action method in it.

[ApiVersion("1.0")]
[Route("api/[controller]")]
[ApiController]
public class PersonController : ControllerBase
{
 [HttpGet]
 public IActionResult Get()
 {
  var person = new { Id = 1, Name = "Naveen" };
  return Ok(person);
 }
}
We created a sample person web API endpoint and decorated the controller with '[ApiVersion("1.0")]'. Let's test this endpoint using the query parameter 'api-version'. Now Navigate to the URL 'https://localhost:44306/api/person?api-version=1.0'.

Resolve ApiVersionUnspecified Issue:

All AspNet Core APIs might not build with versioning from the beginning. If Core API with no versioning used by other clients, later the core API implements  versioning now all the existing clients try to consume API without a version number in the URL, then API fails and returns an error message like 'An API version is required but was not specified.' 
We can understand that calling AspNet Core Web API endpoints without versioning query parameter fails. This will be a problem for existing clients to work with API and it is not a great idea or solution to ask every client to ask to update their API with versioning parameter to their URL.

To Resolve 'ApiVersionUnspecified' issue our ASP.NET Core Web API versioning library provided options like 'AssumeDefaultVersionWhenUnspecified' is boolean whose value by default to false, now set that property to true to work API without version parameter. Update the 'Startup.cs' file as below.

public void ConfigureServices(IServiceCollection services)
{
 services.AddControllers();
 services.AddApiVersioning(options => {
  options.AssumeDefaultVersionWhenUnspecified = true;
 });
}
Now test the API endpoint with and without version parameter

Versioning Between Two Controllers Of Different Names:

One way of versioning Asp.Net Core Web API is to maintain an individual controller for each version. For these endpoints, let's configure attribute routing with their respective version numbers.

MonkeysController.cs:
[ApiVersion("1.0")]
[Route("monkeys")]
[ApiController]
public class MonkeysController : ControllerBase
{
 [HttpGet]
 [Route("")]
 public IActionResult Get()
 {
  var monkey = new { Id = 1, Name = "Forest Monkey" , version = "1.0" };
  return Ok(monkey);
 }
}

MonkeysV2Controller.cs:
[ApiVersion("2.0")]
[Route("monkeys")]
[ApiController]
public class MonkeysV2Controller : ControllerBase
{
 [HttpGet]
 [Route("")]
 public IActionResult Get2()
 {
  var monkey = new { Id = 1, Name = "Zoo Park Monkey", version = "2.0" };
  return Ok(monkey);
 }
}
  • 'MonkeysController' and 'MonkeysV2Controller' API created to represents versions. Both controllers were accessed by attribute routing. 
  • 'ApiVersion' attribute to represent the respective versions of the controller. 
  • 'ApiController' filter is to differentiate between MVC and Web API controllers int Asp.Net Core.
Now test the endpoint as below

If we try the above sample with convention routing, it won't work. Because in conventional based routing we need to point to the controller name while creating a route. If we try to create 2 routes with the same URL and pointing to different controllers, since conventional based routing works on order as a priority it is always going to execute the first registered controller endpoint.

So to make it works in conventional based routing we are going to use '[ControllerName("your_firstversion_controllerName")]' attribute on top of the controller. In Runtime since both controller names are the same virtually, endpoint going to work base on version number provided. Let's update the code to use conventional routing as below
MonkeysV2Controller:

[ApiVersion("2.0")]
[ControllerName("Monkeys")]
[ApiController]
public class MonkeysV2Controller : ControllerBase
{
 [HttpGet]
 public IActionResult Get()
 {
  var monkey = new { Id = 1, Name = "Zoo Park Monkey", version = "2.0" };
  return Ok(monkey);
 }
}
Update the routing in 'Startup.cs' file as below
app.UseEndpoints(endpoints =>
{
 endpoints.MapControllerRoute(
   name: "monkey_route",
   pattern: "monkeys",
   defaults: new { controller = "Monkeys", action = "Get" });
 endpoints.MapControllers();
});


Now run the application, we get a new error "controller annotated with ApiControllerAttribute must be an attributed routed"
This error clearly says that we can't use the 'ApiController' attribute because it enforces us to use the only attribute routing. So let's remove the '[ApiController]' attribute on both controllers file. Test the application again.
Again one more error showing ambiguous Match exception(matching multiple endpoints), because of dotnet core implemented in such a way can work both MVC and Web API controller in a single project. But versioning was mainly to focus on WebAPI, so to resolve this we need to expose our controller as a web API controller by registering '[ApiController]'. But using '[ApiController]' we can't use conventional routing, so this taking us loop of exceptions.

So to resolve this issue we need to change the default behavior of our versioning library, by setting a property 'UseApiBehavior' to false(This will indirectly enable versioning for MVC controllers as well).
Startup.cs:
public void ConfigureServices(IServiceCollection services)
{
 services.AddControllers();
 services.AddApiVersioning(options =>
 {
  options.UseApiBehavior = false;
  options.AssumeDefaultVersionWhenUnspecified = true;
 });
}
Now test the app again, it works perfectly with conventional based routing.

Versioning Between Two Controllers With The Same Name But Different NameSpace:

Controllers versioning differentiate by NameSpace as below.
'v1/BusController.cs':
namespace Web.API.VersioningTest1.Controllers.Buses.v1
{
    [ApiVersion("1.0")]
    [Route("api/[controller]")]
    [ApiController]
    public class BusController : ControllerBase
    {
        [HttpGet]
        [Route("")]
        public IActionResult Get()
        {
            var bus = new { Id = 1, BusType = "Sleeper Bus", Version = "1.0" };
            return Ok(bus);
        }
    }
}
'v2/BusController.cs':
namespace Web.API.VersioningTest1.Controllers.Buses.v2
{
    [ApiVersion("2.0")]
    [Route("api/[controller]")]
    [ApiController]
    public class BusController : ControllerBase
    {
        [HttpGet]
        [Route("")]
        public IActionResult Get()
        {
            var bus = new { Id = 1, BusType = "A/c Bus", Version = "2.0" };
            return Ok(bus);
        }
    }
}
Startup.cs:
public void ConfigureServices(IServiceCollection services)
{
 services.AddControllers();
 services.AddApiVersioning(options =>
 {
  options.AssumeDefaultVersionWhenUnspecified = true;
 });
}
Now run the application and test the URL with both versions

Versioning At Action Methods:

A controller can be decorated with multiple versions and Action methods in it can be decorated with the respective version number using [MapToVersion('your_version_number')]. Let's test it by creating a new example controller as below.
ChocolateController.cs:

[ApiVersion("1.0")]
[ApiVersion("2.0")]
[Route("api/[controller]")]
[ApiController]
public class ChocolateController : ControllerBase
{
 [HttpGet]
 [Route("")]
 public IActionResult Get()
 {
  var chocolate = new { Id = 1, Name = "Kit Kat", Version = "1.0" };
  return Ok(chocolate);
 }

 [HttpGet]
 [Route("")]
 [MapToApiVersion("2.0")]
 public IActionResult GetV2()
 {
  var chocolate = new { Id = 1, Name = "5 star", Version = "2.0" };
  return Ok(chocolate);
 }
}
Here controller was decorated with 2 versions and "GetV2()" action method was mapped to version "2.0" and "Get()" action method by default takes version "1.0". If you don't specify '[MapToApiVersioion("")]' to an action method when the same route is mapped to multiple action methods web API throws an error stating that 'multiple actions are matching'.
Now to work this versioning with conventional based routing update the code as below.
ChocolateController.cs:
namespace Web.API.VersioningTest1.Controllers
{
    [ApiVersion("1.0")]
    [ApiVersion("2.0")]
    public class ChocolateController : ControllerBase
    {
        [HttpGet]
        public IActionResult Get()
        {
            var chocolate = new { Id = 1, Name = "Kit Kat", Version = "1.0" };
            return Ok(chocolate);
        }

        [HttpGet]
        [ActionName("Get")]
        [MapToApiVersion("2.0")]
        public IActionResult GetV2()
        {
            var chocolate = new { Id = 1, Name = "5 star", Version = "2.0" };
            return Ok(chocolate);
        }
    }
}
[ActionName('Get')] attribute helps route to pick the action method based on the version.
Startup.cs:
app.UseEndpoints(endpoints =>
{
endpoints.MapControllerRoute(
 name: "chocolate_route",
 pattern: "chocolate",
 defaults: new { controller = "Chocolate", action = "Get" }
 );

endpoints.MapControllers();
});

public void ConfigureServices(IServiceCollection services)
{
 services.AddControllers();
 services.AddApiVersioning(options =>
 {
  options.UseApiBehavior = false;
  options.AssumeDefaultVersionWhenUnspecified = true;
 });
}

Query String Versioning:

Default versioning enabled was Query String Versioning, till now all samples are done using Query String Versioning. 'api-version' is the query parameter to pass the version number to API.

URL Path Versioning:

In this approach, the version will be part of the URL. This approach does not allow any implicit versioning like in Query String Versioning, So all endpoints need to be registered with the API version attribute explicitly.
Url Path Versioning Ex: "https://someexample.com/v1/test", "https://someexample.com/v2/test".
'v1/BusController.cs':
namespace Web.API.VersioningTest1.Controllers.Buses.v1
{
    [ApiVersion("1.0")]
    [Route("api/v{version:apiVersion}/[controller]")]
    [ApiController]
    public class BusController : ControllerBase
    {
        [HttpGet]
        [Route("")]
        public IActionResult Get()
        {
            var bus = new { Id = 1, BusType = "Sleeper Bus", Version = "1.0" };
            return Ok(bus);
        }
    }
}
'v2/BusController.cs':
namespace Web.API.VersioningTest1.Controllers.Buses.v2
{
    [ApiVersion("2.0")]
    [Route("api/v{version:apiVersion}/[controller]")]
    [ApiController]
    public class BusController : ControllerBase
    {
        [HttpGet]
        [Route("")]
        public IActionResult Get()
        {
            var bus = new { Id = 1, BusType = "A/c Bus", Version = "2.0" };
            return Ok(bus);
        }
    }
}
In the Attribute route given a placeholder like an object literal '{version: apiVersion}', this the place where our version number gets injected. Now test the application by navigating to URLs like 'https://localhost:44306/api/v1/bus' and 'https://localhost:44306/api/v2/bus'.

In the URL placeholder key-value pair, we can give any name to the key but the value must be 'apiVersion'Once try to change the object literal value an error will be shown as below

MediaType Versioning:

MediaType versioning is passing the version number along with the content-type of a web API. To use this versioning we need to need to assign 'MediaTypeApiVersionReader' to 'ApiVersionReader' in service configurations. If no version is sent API returns the latest version data. Update the code as below.
'v1/BusController.cs':

namespace Web.API.VersioningTest1.Controllers.Buses.v1
{
    [ApiVersion("1.0")]
    [Route("api/[controller]")]
    [ApiController]
    public class BusController : ControllerBase
    {
        [HttpGet]
        [Route("")]
        public IActionResult Get()
        {
            var bus = new { Id = 1, BusType = "Sleeper Bus", Version = "1.0" };
            return Ok(bus);
        }
    }
}
'v2/BusController.cs':
namespace Web.API.VersioningTest1.Controllers.Buses.v2
{
    [ApiVersion("2.0")]
    [Route("api/[controller]")]
    [ApiController]
    public class BusController : ControllerBase
    {
        [HttpGet]
        [Route("")]
        public IActionResult Get()
        {
            var bus = new { Id = 1, BusType = "A/c Bus", Version = "2.0" };
            return Ok(bus);
        }
    }
}

Startup.cs:
public void ConfigureServices(IServiceCollection services)
{
 services.AddControllers();
 services.AddApiVersioning(options =>
 {
  options.ApiVersionReader = new MediaTypeApiVersionReader();
  options.AssumeDefaultVersionWhenUnspecified = true;
  options.ApiVersionSelector = new CurrentImplementationApiVersionSelector(options);
 });
}
  • 'MediaTypeApiVersionReader' force to read the versioning from the media type. 
  • 'CurrentImplementationApiVersionSelector' Represents API version selector which selects the API version of the most current implementation of the requested service.
Now test endpoint without passing version with a media type, we can observe the latest version of API data will return
Now test endpoint with a version number along with a media type

Notify Supported And Deprecated API Versions:

It is always a better idea to show supported and deprecated API versions to the clients that are consuming the API. To make API  deprecated need pass boolean value true for version attribute and
to display the information about the versions of an API configure 'ReportApiVersion' to true at the service registration. This API Deprecation means that a particular version going to be deleted very soon.
'v1/BusController.cs':

namespace Web.API.VersioningTest1.Controllers.Buses.v1
{
    [ApiVersion("1.0",Deprecated =true)]
    [Route("api/[controller]")]
    [ApiController]
    public class BusController : ControllerBase
    {
        [HttpGet]
        [Route("")]
        public IActionResult Get()
        {
            var bus = new { Id = 1, BusType = "Sleeper Bus", Version = "1.0" };
            return Ok(bus);
        }
    }
}
Startup.cs:
public void ConfigureServices(IServiceCollection services)
{
 services.AddControllers();
 services.AddApiVersioning(options =>
 {
  options.AssumeDefaultVersionWhenUnspecified = true;
  options.ReportApiVersions = true;
 });
}
Now test endpoint

Summary:

We have implemented samples of ASP.NET Core Web API versioning. We discussed the different styles of coding versioning and different types of versioning. Discussed how to resolve the most common errors that are faced while implementing versioning. Discussed how to notify about the information about clients consuming API.

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