ASP.NET Web API中把分页信息放Header中返回给前端

谈到ASP.NET Web API的分页，考虑的因素包括：

1、上一页和下一页的uri
2、总数和总页数
3、当前页和页容量

接着是服务端的数据以怎样的形式返回？

我们通常这样写：

{
totalCount:10,
result: [
{id:1, name:"a"},
{id:2, name:"b"}
]
}

以上，把分页相关和实体信息以json格式返回给前端。但在本篇，尝试另外一种方式：把分页信息放在Header中返回给前端。

const int maxPageSize = 10;

[Route("api/items", Name="items")]
public IHttpActionResult Get(int page = 1, ing pageSize = 5)
{
try
{
var items = _repo.GetItem()
.sort()
.Where();

if(pageSize > maxPageSize)
{
pageSize = maxPageSize;
}

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

var urlHelper = new UrlHelper(Request);
var prevLink = page > 1 ? UrlHeloer.Link("items", new {
page = page -1,
pageSize = pageSize,
...
}) : "";

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

var paginationHeader = new
{
currentPage = page,
pageSize = pageSize,
totalCount = totalCount,
totalPages = totalPages,
previousPageLink = prevLink,
nextPageLink = nextLink
};

//放到Header中
HttpContext.Current.Response.Headers.Add("X-Pagination", Newtonsoft.Json.JsonConvert.SerializeObject(paginationHeader));

var result = items
.Skip(pageSize * (page - 1))
.Take(pageSize)
.ToList()
.Select(e => ItemFactory.CreateItem(e));

return Ok(result);

}
catch(Exception)
{
//TODO:处理异常
}
}

客户端发出如下请求：

localhost:4321/api/items?page=2&pagesize=2

在响应中有一个X-Pagination属性：

X-Pagination:{
"currentPage":2,
"pageSize":2,
"totalPages":4,
"previousPageLink": "http://localhost:4321/api/items?page=1&pageSize=2"
"nextPageLink":"http://localhost:4321/api/items?page=3&pageSize=2"
}