LINQ到實體無法識別方法「System.Linq.IQueryable`1

Question

當我執行下面的代碼：

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

返回設爲myVal如預期的整數值，但如果我嘗試並返回IQueryable的作爲下面

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()) 
}); 

我得到的錯誤：

LINQ到實體無法識別方法 「SYST em.Linq.IQueryable`1 [DestKosher.Model.HotelModel] GetHotelsByCityId（的Int32）」方法，和這種方法不能被翻譯成 商店表達。

該方法hotelDataAccess.GetHotelsByCityId（19）返回IQueryable。任何想法，幫助或解決方案將不勝感激。問候，

馬丁

UPDATE：

該查詢最初設置，查看是否通過將一個整數到功能GetHotelsByCityId會工作。不過，我想最終做的是：

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

通過設計，LINQ to Entities需要整個LINQ查詢表達式轉換爲服務器查詢。只有少數不相關的子表達式（在不依賴於來自服務器的結果的查詢表達式）在客戶端上評估的查詢翻譯前。不支持任何方法調用，例如GetHotelsByCityId（）在這種情況下不具有已知的翻譯。

你可以像這樣

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

比我們在設爲myVal查詢

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瞭解更多Deatil：LINQ to Entities, what is not supported?

Answer 2

嘗試增加命名空間 「System.Linq的」，也如果您有「System.Core」程序集引用，請檢查您的項目引用。