Question

我正在使用LINQ，我想通过传递参数来调用方法（例如checkOpenClose），并让它返回true / false：

var model = (from account in _ctx.Account
             where (...)
             select new DetailVM
             {
               Id = account.Id,
               Name = account.CompanyName,
               OpenNow = checkOpenClose(account.MonOpen, account.MonClosed,           
                           account.TueOpen, account.TueClosed,
                           account.WedOpen, account.WedClosed,
                           account.ThuOpen, account.ThuClosed,
                           account.FriOpen, account.FriClosed,
                           account.SatOpen, account.SatClosed,
                           account.SunOpen, account.SunClosed)
             }).Tolist()

我收到以下错误：

LINQ to Entities无法识别方法'Boolean checkOpenClose （System.String，System.String，System.String，System.String， System.String，System.String，System.String，System.String， System.String，System.String，System.String，System.String， System.String，System.String）'方法，而这个方法不可能翻译成商店表达。

我做错了什么？

Answer 1

请记住，查询将被转换为sql，因此您的Linq提供程序无法将您的方法调用转换为有效的方法。如果您确实需要调用该方法，那么我建议调用AsEnumerable扩展方法，如下所示：

   var model=    (from account in _ctx.Account
                  where (...)
                  select account)
                 .AsEnumerable()
                 .Select(account=> new DetailVM
                                   {
                                      Id = account.Id,
                                      Name = account.CompanyName,
                                      OpenNow = checkOpenClose(account.MonOpen, account.MonClosed,
                                                               account.TueOpen, account.TueClosed,
                                                               account.WedOpen, account.WedClosed,
                                                               account.ThuOpen, account.ThuClosed,
                                                               account.FriOpen, account.FriClosed,
                                                               account.SatOpen, account.SatClosed,
                                                               account.SunOpen, account.SunClosed)


                                    })
                .Tolist();

这将允许您使用Linq to Objects

执行所需的投影

Answer 2

正如我所见，您正在使用实体框架datacontext，它将linq语句转换为sql脚本，因此当您使用方法时，它无法将其转换为sql。试试这个

var model= (from account in _ctx.Account
                      where (...)
                      select new {
                          Id = account.Id,
                          Name = account.CompanyName,
                          MO = account.MonOpen, 
                          MC = account.MonClosed,
                          TUO = account.TueOpen, 
                          TUC = account.TueClosed,
                          WO = account.WedOpen,
                          WC = account.WedClosed,
                          THO = account.ThuOpen, 
                          THC = account.ThuClosed,
                          FO = account.FriOpen,
                          FC = account.FriClosed,
                          SO = account.SatOpen,
                          SC = account.SatClosed,
                          SUO = account.SunOpen,
                          SUC = account.SunClosed

                          }).Tolist().select(m=> new DetailVM {

                        Id = account.Id,
                        Name = account.CompanyName,
                        OpenNow = checkOpenClose(MO,MC,TUO,TUC,WO,WC,THO,THC,FO,FC,SO,SC,SUO,SUC)

            }).ToList();

Answer 3

你的布尔方法中有没有SQL对应的表达式...这已经在SO上充实了几次看

EF needs expressions that have an SQL equivalent

或

another from SO

LINQ中的c＃调用方法

3 个答案: