实现资源分页
本章我们将介绍几种不同的结果集分页方式，实现手工分页，然后将Response通过两个不同的方式进行格式化（通过Response的Envelop元数据或header）。
大家都知道一次查询返回几百条数据是很讨厌的事情，那么在WebApi中分页就更有必要。
手动分页和封装
接下来我们修改CoursesController来实现分页而不是返回所有数据。
1: public Object Get(int page = 0, int pageSize = 10)
2: {
3: IQueryable<Course> query;
4:
5: query = TheRepository.GetAllCourses().OrderBy(c => c.CourseSubject.Id);
6: var totalCount = query.Count();
7: var totalPages = (int)Math.Ceiling((double)totalCount / pageSize);
8:
9: var urlHelper = new UrlHelper(Request);
10: var prevLink = page > 0 ? urlHelper.Link("Courses", new { page = page - 1 }) : "";
11: var nextLink = page < totalPages - 1 ? urlHelper.Link("Courses", new { page = page + 1 }) : "";
12:
13: var results = query
14: .Skip(pageSize * page)
15: .Take(pageSize)
16: .ToList()
17: .Select(s => TheModelFactory.Create(s));
18:
19: return new
20: {
21: TotalCount = totalCount,
22: TotalPages = totalPages,
23: PrevPageLink = prevLink,
24: NextPageLink = nextLink,
25: Results = results
26: };
27:
28: }
.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }
代码很简单，添加两个可选参数，它们最终会被格式化为QueryString。例如http://localhost:{your_port}/api/courses/?page=1代表你需要访问第一页的10条数据。不出意外，结果可能是这样的：
1: {
2:
3: "totalCount": 33,
4: "totalPages": 4,
5: "prevPageLink": "http://localhost:8323/api/courses?page=0&pageSize=10",
6: "nextPageLink": "http://localhost:8323/api/courses?page=2&pageSize=10",
7: "results": [ /* Array containts the results*/ ]
8:
9: }
结果是我们通过将数据封装为json通过Response的结果返回，这样记录总数也可以被返回。一个明显的缺点是这种类似的数据可能会污染我们期望的结果集，所以接下来我们通过在Response Header中添加一个X-Pagination参数来实现这一功能。
通过Response Header实现分页
实现代码如下：
1: public IEnumerable<StudentBaseModel> 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 = (int)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.F.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.CreateSummary(s));
30:
31: return results;
32: }
.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }
需要注意代码中，我们在Response.Headers中添加了一个通过json序列化的分页参数。这样返回结果及就可以直接被使用，无法再考虑额外的信息。
来源：http://bitoftech.net/2013/11/25/implement-resources-pagination-asp-net-web-api/