using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;

public class ItemsController : ApiController
{
    ...
    [HttpGet]
    [Queryable]
    public IQueryable<Item> GetItems()
    {
        return _repository.Items.AsQueryable();
    }

但Visual Studio告诉我

‘Queryable’ is not an attribute”

我收到编译错误：

CS0616: ‘System.Linq.Queryable’ is not an attribute class

如果我符合该属性

[System.Web.Http.Queryable]

我收到另一条错误消息

CS0234: The type or namespace name ‘Queryable’ does not exist in the
namespace ‘System.Web.Http’ (are you missing an assembly reference?)

任何想法为什么[可查询]似乎没有被识别？这是一个Web表单应用程序,以后会添加Web API.