Query String Versioning

The initial version of a controller may not have any API version attribution and will implicitly become the configured default API version. The default configuration uses the value 1.0.

Minimal API

var builder = WebApplication.CreateBuilder( args );

builder.Services.AddProblemDetails();
builder.Services.AddApiVersioning();

var app = builder.Build();
var hello = app.NewVersionedApi();
var v1 = hello.MapGroup( "/helloworld" ).HasApiVersion( 1.0 );
var v2 = hello.MapGroup( "/helloworld" ).HasApiVersion( 2.0 );

v1.MapGet( "/", () => "Hello world!" );
v2.MapGet( "/", () => "Hello world!" );

app.Run();

MVC (Core)

[ApiController]
[Route( "api/[controller]" )]
public class HelloWorldController : ControllerBase
{
    [HttpGet]
    public string Get() => "Hello world!";
}

OData

public class PeopleController : ODataController
{
    [HttpGet]
    public IHttpActionResult Get( ODataQueryOptions<Person> options ) =>
        Ok( new[]{ new Person() } );
}

Next Version

To create the next version of the controller, you can choose to create a new controller with the same route but decorate it as API version 2.0. For example:

MVC (Core)

[ApiVersion( 2.0 )]
[ApiController]
[Route( "api/helloworld" )]
public class HelloWorld2Controller : ControllerBase
{
    [HttpGet]
    public string Get() => "Hello world!";
}

OData

[ApiVersion( 2.0 )]
[ControllerName( "People" )]
public class People2Controller : ODataController
{
    [HttpGet]
    public IHttpActionResult Get( ODataQueryOptions<Person> options ) =>
        Ok( new[]{ new Person() } );
}

The effect of this attribution is that the following requests match different controller implementations:

It’s important to note that only an undecorated controller will be inferred as the configured, default API version. Once a controller has any API version attribution, it will never be considered as the default API version again unless the API version attribute includes the default API version. This allows you permanently remove API versions over time.