CS0266 无法转换类型

Question

我有一个错误：

CS0266 C# 不能隐式转换类型 'System.Linq.IQueryable' 到 'System.Linq.IOrderedIQueryable'。一个 存在显式转换（您是否缺少演员表？）

这是我的控制器：

public ViewResult Index(string sortOrder, string currentFilter, string searchString, int? page)
{
    ViewBag.CurrentSort = sortOrder;
    ViewBag.NameSurnameSortParm = sortOrder == "NameSurname" ? "NameSurname_desc" : "NameSurname";
    ViewBag.ReasonSortParm = sortOrder == "Reason" ? "Reason_desc" : "Reason";
    ViewBag.AccessSortParm = sortOrder == "Access" ? "Access_desc" : "Access";
    ViewBag.UserOrAdminSortParm = sortOrder == "UserOrAdmin" ? "UserOrAdmin_desc" : "UserOrAdmin";

    ViewBag.DepartmentSortParm = sortOrder == "Department" ? "Department_desc" : "Department";
    ViewBag.UNCPathSortParm = sortOrder == "UNCPath" ? "UNCPath_desc" : "UNCPath";

    if (searchString != null)
    {
        page = 1;
    }

    else
    {
        searchString = currentFilter;
    }

    ViewBag.CurrentFilter = searchString;

    var request = from c in _context.RaidRequest
                    orderby c.Id
                    select c;

    if (!String.IsNullOrEmpty(searchString))
    {
        request = request.Where(s => s.NameSurname.Contains(searchString));
    }

    switch (sortOrder)
    {
        case "NameSurname_desc":
            request = request.OrderByDescending(c => c.NameSurname);
            break;
        case "Reason":
            request = request.OrderBy(c => c.Reason);
            break;
        case "Reason_desc":
            request = request.OrderByDescending(c => c.Reason);
            break;
        case "Access":
            request = request.OrderBy(c => c.Access);
            break;
        case "Access_desc":
            request = request.OrderByDescending(c => c.Access);
            break;
        case "UserOrAdmin":
            request = request.OrderBy(c => c.UserOrAdmin);
            break;
        case "UserOrAdmin_desc":
            request = request.OrderByDescending(c => c.UserOrAdmin);
            break;
        case "Department":
            request = request.OrderBy(c => c.Department);
            break;
        case "Department_desc":
            request = request.OrderByDescending(c => c.Department);
            break;
        case "UNCPath":
            request = request.OrderBy(c => c.UNCPath);
            break;
        case "UNCPath_desc":
            request = request.OrderByDescending(c => c.UNCPath);
            break;
    }

    int pageSize = 10;
    int pageNumber = (page ?? 1);
    return View(request.ToPagedList(pageNumber, pageSize));
}

这部分坏了：

if (!String.IsNullOrEmpty(searchString))
{
    request = request.Where(s => s.NameSurname.Contains(searchString));
}

你能解释一下该怎么做吗？ 我一个字一个字地跟着教程。在我添加分页之前它一直有效。 会不会是我的观点？

Answer 1

您的所有查询都包含一个 orderby，因此返回一个 IOrderedQueryable，除了您使用搜索字符串的查询。此查询返回IQueryable。

由于IOrderedQueryable 继承自IQueryable，因此您可以将IOrderedQueryable 分配给IQueryable，但反之则不行。

从第一个查询中删除orderby，它会变成IQueryable，在switch语句中添加default:进行默认排序。这也将阻止您对结果查询进行两次排序。

    var request = from c in _context.RaidRequest
                      select c;

    // Your code
    switch (sortOrder)
        {
            // other cases
            case "UNCPath_desc":
                request = request.OrderByDescending(c => c.UNCPath);
                break;
            default: 
                request = request.OrderBy(c => c.Id);
                break;
        }