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，但是如果我尝试如下返回 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())
 });

我得到了错误：

LINQ to Entities 无法识别该方法 'System.Linq.IQueryable`1[DestKosher.Model.HotelModel] GetHotelsByCityId(Int32)' 方法，这个方法不能翻译 到商店表达式中。

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

马丁

更新：

最初设置此查询是为了查看将整数放入函数 GetHotelsByCityId 是否有效。但是，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。在翻译查询之前，只有少数不相关的子表达式（查询中不依赖于服务器结果的表达式）在客户端上进行评估。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 
 });

阅读更多详情：LINQ to Entities, what is not supported?

Answer 2

尝试添加命名空间“System.Linq”，如果您有“System.Core”程序集引用，请检查您的项目引用。