[翻译]创建ASP.NET WebApi RESTful 服务（9）

一旦成功的发布API后，使用者将依赖于你所提供的服务。但是变更总是无法避免的，因此谨慎的制定ASP.NET Web API的版本策略就变得非常重要。一般来说，新的功能需要无缝的接入，有时新老版本需要并行，以便给使用者足够的时间来进行迁移和配套的变更。设置，老的版本会一直持续被使用。

简单版本管理

假设我们现在对StudentsController进行修改，将GET方法中返回“FirstName” 和 “LastName”修改为返回“FullName”和 “CoursesDuration”。

最简单的方法就是新建一个类似于StudentsV2Controller的新服务。请留意V2，接下来将依赖这个引入管理策略。这种方法来自于Shawn Wildermuth的plural sight course文章。旧版本的服务返回的json应该是这样的：

   1:  [{

   2:      "id": 2,

   3:      "url": "http://localhost:8323/api/students/HasanAhmad",

   4:      "firstName": "Hasan",

   5:      "lastName": "Ahmad",

   6:      "gender": 0,

   7:      "enrollmentsCount": 4

   8:  },

   9:  {

  10:      "id": 3,

  11:      "url": "http://localhost:8323/api/students/MoatasemAhmad",

  12:      "firstName": "Moatasem",

  13:      "lastName": "Ahmad",

  14:      "gender": 0,

  15:      "enrollmentsCount": 4

  16:  }]

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而新版本的返回如下：

   1:  [{

   2:      "id": 2,

   3:      "url": "http://localhost:8323/api/students/HasanAhmad",

   4:      "fullName": "Hasan Ahmad",

   5:      "gender": 0,

   6:      "enrollmentsCount": 4,

   7:      "coursesDuration": 13

   8:  },

   9:  {

  10:      "id": 3,

  11:      "url": "http://localhost:8323/api/students/MoatasemAhmad",

  12:      "fullName": "Moatasem Ahmad",

  13:      "gender": 0,

  14:      "enrollmentsCount": 4,

  15:      "coursesDuration": 16

  16:  }]

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新版本的GET函数的实现为：

   1:  public IEnumerable<StudentV2BaseModel> Get(int page = 0, int pageSize = 10)

   2:      {

   3:          IQueryable<Student> query;

   4:   

   5:          query = TheRepository.GetAllStudentsWithEnrollments().OrderBy(c => c.LastName);

   6:   

   7:          var totalCount = query.Count();

   8:          var totalPages = Math.Ceiling((double)totalCount / pageSize);

   9:   

  10:          var urlHelper = new UrlHelper(Request);

  11:          var prevLink = page > 0 ? urlHelper.Link("Students", new { page = page - 1, pageSize = pageSize }) : "";

  12:          var nextLink = page < totalPages - 1 ? urlHelper.Link("Students", new { page = page + 1, pageSize = pageSize }) : "";

  13:   

  14:          var paginationHeader = new

  15:          {

  16:              TotalCount = totalCount,

  17:              TotalPages = totalPages,

  18:              PrevPageLink = prevLink,

  19:              NextPageLink = nextLink

  20:          };

  21:   

  22:          System.Web.HttpContext.Current.Response.Headers.Add("X-Pagination",

  23:          Newtonsoft.Json.JsonConvert.SerializeObject(paginationHeader));

  24:   

  25:          var results = query

  26:          .Skip(pageSize * page)

  27:          .Take(pageSize)

  28:          .ToList()

  29:          .Select(s => TheModelFactory.CreateV2Summary(s));

  30:   

  31:          return results;

  32:      }

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StudentV2BaseModel和CreateV2Summary只是为了举例方便，实际可以根据需要是否要进行这样的修改或者无须修改。

具体的代码如下：

   1:  public class StudentV2BaseModel

   2:      {

   3:          public int Id { get; set; }

   4:          public string Url { get; set; }

   5:          public string FullName { get; set; }

   6:          public Data.Enums.Gender Gender { get; set; }

   7:          public int EnrollmentsCount { get; set; }

   8:          public double CoursesDuration { get; set; }

   9:      }

  10:   

  11:      public class ModelFactory

  12:      {

  13:          public StudentV2BaseModel CreateV2Summary(Student student)

  14:          {

  15:              return new StudentV2BaseModel()

  16:              {

  17:                  Url = _UrlHelper.Link("Students", new { userName = student.UserName }),

  18:                  Id = student.Id,

  19:                  FullName = string.Format("{0} {1}", student.FirstName, student.LastName),

  20:                  Gender = student.Gender,

  21:                  EnrollmentsCount = student.Enrollments.Count(),

  22:                  CoursesDuration = Math.Round(student.Enrollments.Sum(c => c.Course.Duration))

  23:              };

  24:          }

  25:      }

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来源：http://bitoftech.net/2013/12/16/asp-net-web-api-versioning-strategy/