应用是演进的，通常我们用版本号来管理。api也是演进的，这篇博文就说说asp.net web api演进时的版本管理。

　　asp.net web api的版本管理是通过微软的一个包来实现的。

　　Install-Package Microsoft.AspNetCore.Mvc.Versioning

通过url参数: api/order/api-version=2.0

　　在startup中注入ApiVersion

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

　　在ProductController中标注版本特性

using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace APIVersionDemo.Controllers
{
    [ApiController]
    [Route("api/[controller]")]
    [ApiVersion("1.0", Deprecated = true)]
    [ApiVersion("2.0")]
    public class ProductController : ControllerBase
    {
        private readonly ILogger<ProductController> _logger;
        public ProductController(ILogger<ProductController> logger)
        {
            _logger = logger;
        }
        //1.0的api
        [HttpGet("{id}")]
        public Product QueryProduct([FromRoute] int id)
        {
            _logger.LogInformation("v1.0查询产品");
            return new Product() { ID = id, Name = "A物品", Price = 100.20m };
        }

        //2.0的api
        [HttpGet("{id}")]
        [MapToApiVersion("2.0")]
        public Product QueryProductv2([FromRoute] int id)
        {
            _logger.LogInformation("v2.0查询产品");
            return new Product2() { ID = id, Name = "A物品", Price = 100.20m, Description = "产自山西" };
        }   
    }
    /// <summary>
    /// 1.0的产品类
    /// </summary>
    public class Product
    {
        public int ID { get; set; }
        public string Name { get; set; }
        public decimal Price { get; set; }
    }
    /// <summary>
    /// 2.0的产品类
    /// </summary>
    public class Product2 : Product
    {
        public string Description { get; set; }
    }
}

　　通过http://localhost:5000/api/product/1?api-version=2.0方式访问不同的版本。显而易见，这种通过在请求url末尾加参数的方式有点啰嗦。

　　通过MediaType：{Accept:application/json;version=2.0}或header：{version:2.0}

　　修改startup的apiversion注入参数

  public void ConfigureServices(IServiceCollection services)
        {
            services.AddApiVersioning(opt =>
            {
                opt.AssumeDefaultVersionWhenUnspecified = true;
                opt.DefaultApiVersion = new ApiVersion(1, 0);
                opt.ApiVersionReader = ApiVersionReader.Combine(
                    new MediaTypeApiVersionReader("version"),
                    new HeaderApiVersionReader("api-version")
                    );
                opt.ReportApiVersions = true;
            });
            services.AddControllers();
        }

　　ProductController不变。

　　请求http://localhost:5000/api/product/1,header参数，可以适配两种方式：Accept  :  application/json;version=2.0api-version  :  2.0
　　这样方便客户端请求的整体处理。

通过url:api/v2.0/order

　　strartup.cs注入apiversion

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

　　这里引入OrderController，在Route特性上改变url，在url里增加版本信息{version:apiVersion}

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.ApplicationModels;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace APIVersionDemo.Controllers
{
    [ApiController]
    [Route("api/v{version:apiVersion}/[controller]")]
    [ApiVersion("1.0", Deprecated = true)]
    [ApiVersion("2.0")]
    public class OrderController : ControllerBase
    {
        private readonly ILogger<OrderController> _logger;
        public OrderController(ILogger<OrderController> logger)
        {
            _logger = logger;
        }
        //v1订单api
        [HttpGet("{id}")]
        public Order QueryOrder()
        {
            _logger.LogInformation("v1查询产品");
            return new Order()
            {
                OrderID = 1,
                Products = new List<Product>()
                {
                    new Product() { ID = 1, Name = "A物品", Price = 100.20m }
                }
            };
        }
       //v2订单api
        [HttpGet("{id}")]
        [MapToApiVersion("2.0")]
        public Order2 QueryOrder2()
        {
            _logger.LogInformation("v2查询产品");
            return new Order2()
            {
                OrderID = 1,
                Products = new List<Product2>()
                {
                new Product2() { ID = 1, Name = "A物品", Price = 100.20m, Description = "产自山西" }
                }
            };
        }
    }
   //v1订单类
    public class Order
    {
        public int OrderID { get; set; }
        public List<Product> Products { get; set; }
    }
    //v2订单类
    public class Order2
    {
        public int OrderID { get; set; }
        public List<Product2> Products { get; set; }
    }
}

　　这时请求就变成http://localhost:5000/api/v2.0/order了，可以通过不同的url来访问不同的api版本，这种方式也有利于客户端统一配置baseurl，来切换请求api版本。

　　最后，apiversion这个包还带来了一个无侵入controller的方式来配置api的版本，本质与加在Controller上的特性信息是一致的——附加版本信息和对应关系。

services.AddApiVersioning(opt =>
{              
       opt.Conventions.Controller<ProductController>()
          .HasApiVersion(2, 0)
          .HasDeprecatedApiVersion(1, 0)
          .Action(typeof(ProductController)
          .GetMethod(nameof(ProductController.QueryProductv2))!)
          .MapToApiVersion(2, 0);
});