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

新建一个DemoResponse.cs文件

namespace AspNetCoreVersioning.Contracts {  
    public class DemoResponseV1 {  
        public Guid Id {  
            get;  
            set;  
        }  
        public string Name {  
            get;  
            set;  
        }  
    }  
    public class DemoResponseV2 {  
        public Guid Id {  
            get;  
            set;  
        }  
        public string DemoName {  
            get;  
            set;  
        }  
    }  
}  

添加ApiVersioningDemoController.cs

namespace AspNetCoreVersioning.Controllers {  
    [ApiController]  
    [Route("api/demos")]  
    public class ApiVersioningDemoController: ControllerBase {  
        [HttpGet("{demoId}")]  
        public IActionResult GetDemo([FromRoute] Guid demoId) {  
            var demo = new DemoResponse {  
                Id = demoId,  
                    Name = "api demo"  
            };  
            return Ok(demo);  
        }  
    }  
}  

namespace AspNetCoreVersioning.Controllers {  
    [ApiController]  
    [Route("api/demos")]  
    [ApiVersion("1.0")]  
    [ApiVersion("2.0")]  
    public class ApiVersioningDemoController: ControllerBase {  
        [HttpGet("{demoId}")]  
        public IActionResult GetDemoV1([FromRoute] Guid demoId) {  
                var demo = new DemoResponseV1 {  
                    Id = demoId,  
                        Name = "demo v1 "  
                };  
                return Ok(demo);  
            }  
            [HttpGet("{demoId}")]  
            [MapToApiVersion("2.0")]  
        public IActionResult GetDemoV2([FromRoute] Guid demoId) {  
            var demo = new DemoResponseV2 {  
                Id = demoId,  
                    DemoName = "demo v2"  
            };  
            return Ok(demo);  
        }  
    }  
}  

运行测试

https://localhost.57327/api/demos/00000000-0000-0000-0000-000000000000?api-version=1

输出

Result: {"id":"00000000-0000-0000-0000-000000000000","name":"demo v1"} 

https://localhost:57327/api/demos/00000000-0000-0000-0000-000000000000?api-version=2

Result: {"id":"00000000-0000-0000-0000-000000000000","demoName":"demo v2"}