[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：

[{
    "id": 2,
    "url": "http://localhost:8323/api/students/HasanAhmad",
    "firstName": "Hasan",
    "lastName": "Ahmad",
    "gender": 0,
    "enrollmentsCount": 4
},
{
    "id": 3,
    "url": "http://localhost:8323/api/students/MoatasemAhmad",
    "firstName": "Moatasem",
    "lastName": "Ahmad",
    "gender": 0,
    "enrollmentsCount": 4
}]

而新版本的返回如下：

[{
    "id": 2,
    "url": "http://localhost:8323/api/students/HasanAhmad",
    "fullName": "Hasan Ahmad",
    "gender": 0,
    "enrollmentsCount": 4,
    "coursesDuration": 13
},
{
    "id": 3,
    "url": "http://localhost:8323/api/students/MoatasemAhmad",
    "fullName": "Moatasem Ahmad",
    "gender": 0,
    "enrollmentsCount": 4,
    "coursesDuration": 16
}]

新版本的GET函数的实现为：

public IEnumerable<StudentV2BaseModel> Get(int page = 0, int pageSize = 10)
    {
        IQueryable<Student> query;

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

        var totalCount = query.Count();
        var totalPages = Math.Ceiling((double)totalCount / pageSize);

        var urlHelper = new UrlHelper(Request);
        var prevLink = page > 0 ? urlHelper.Link("Students", new { page = page - 1, pageSize = pageSize }) : "";
        var nextLink = page < totalPages - 1 ? urlHelper.Link("Students", new { page = page + 1, pageSize = pageSize }) : "";

        var paginationHeader = new
        {
            TotalCount = totalCount,
            TotalPages = totalPages,
            PrevPageLink = prevLink,
            NextPageLink = nextLink
        };

        System.Web.HttpContext.Current.Response.Headers.Add("X-Pagination",
        Newtonsoft.Json.JsonConvert.SerializeObject(paginationHeader));

        var results = query
        .Skip(pageSize * page)
        .Take(pageSize)
        .ToList()
        .Select(s => TheModelFactory.CreateV2Summary(s));

        return results;
    }

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：

public class StudentV2BaseModel
    {
        public int Id { get; set; }
        public string Url { get; set; }
        public string FullName { get; set; }
        public Data.Enums.Gender Gender { get; set; }
        public int EnrollmentsCount { get; set; }
        public double CoursesDuration { get; set; }
    }

    public class ModelFactory
    {
        public StudentV2BaseModel CreateV2Summary(Student student)
        {
            return new StudentV2BaseModel()
            {
                Url = _UrlHelper.Link("Students", new { userName = student.UserName }),
                Id = student.Id,
                FullName = string.Format("{0} {1}", student.FirstName, student.LastName),
                Gender = student.Gender,
                EnrollmentsCount = student.Enrollments.Count(),
                CoursesDuration = Math.Round(student.Enrollments.Sum(c => c.Course.Duration))
            };
        }
    }

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