c# - LINQ to Entities 无法识别方法 'System.Linq.IQueryable` 1

Question

当我执行以下代码时:

IHotelDataAccess _hotelDataAccess= new HotelDataAccess(_entities);
int myVal = (from u in _hotelDataAccess.GetHotelsByCityId(19)
    select u).Count();

myVal 按预期返回一个整数值，但是如果我尝试返回如下所示的 IQueryable

return (from geoLocation in _entities.ViewGeographyLocation
 where geoLocation.CountryCode == countryCode
 orderby geoLocation.SortOrder, geoLocation.CityName
 select new ContinentModel
 {
  ContinentCode = geoLocation.ContinentCode,
  ContinentName = geoLocation.ContinentName,
  CountryCode = geoLocation.CountryCode,
  CountryName = geoLocation.CountryName,
  CityId = geoLocation.CityId,
  CityName = geoLocation.CityName,
  CityCode = geoLocation.CityName,
  TotalCount = ((from u in _hotelDataAccess.GetHotelsByCityId(19)
   select u).Count())
 });

我收到错误:

LINQ to Entities does not recognize the method 'System.Linq.IQueryable`1[DestKosher.Model.HotelModel] GetHotelsByCityId(Int32)' method, and this method cannot be translated into a store expression.

方法 hotelDataAccess.GetHotelsByCityId(19) 返回 IQueryable。任何想法、帮助或解决方案将不胜感激。问候，

马丁

更新:

此查询最初设置是为了查看将整数放入函数 GetHotelsByCityId 中是否可行。然而，我最终想做的是:

return (from geoLocation in _entities.ViewGeographyLocation
 where geoLocation.CountryCode == countryCode
 orderby geoLocation.SortOrder, geoLocation.CityName
 select new ContinentModel
 {
  ContinentCode = geoLocation.ContinentCode,
  ContinentName = geoLocation.ContinentName,
  CountryCode = geoLocation.CountryCode,
  CountryName = geoLocation.CountryName,
  CityId = geoLocation.CityId,
  CityName = geoLocation.CityName,
  CityCode = geoLocation.CityName,
  TotalCount = ((from u in _hotelDataAccess.GetHotelsByCityId(geoLocation.CityId)
   select u).Count())
 });

Answer 1

根据设计， LINQ to Entities 需要将整个 LINQ 查询表达式转换为服务器查询。在转换查询之前，仅​​在客户端上计算一些不相关的子表达式(查询中不依赖于服务器结果的表达式)。不支持没有已知转换的任意方法调用，例如本例中的 GetHotelsByCityId()。

你可以这样做

var list = _hotelDataAccess.GetHotelsByCityId(19).ToList();
int myVal = (from u in list
    select u).Count();

在您的查询中比我们 myval

return (from geoLocation in _entities.ViewGeographyLocation
 where geoLocation.CountryCode == countryCode
 orderby geoLocation.SortOrder, geoLocation.CityName
 select new ContinentModel
 {
  ContinentCode = geoLocation.ContinentCode,
  ContinentName = geoLocation.ContinentName,
  CountryCode = geoLocation.CountryCode,
  CountryName = geoLocation.CountryName,
  CityId = geoLocation.CityId,
  CityName = geoLocation.CityName,
  CityCode = geoLocation.CityName,
  TotalCount = myVal 
 });

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