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