LINQ 到實體框架多對多，帶有字符串列表

Question

這個問題是從以下繼續： Can't think of query that solve this many to many

用戶@juharr 向我推薦了這個 LINQ 查詢，我只是添加了字符串連接，目的是將名字和姓氏組合成全名。

var courseViews = from c in db.Courses  
                  select new CourseView()  
                  {  
                      CourseID = c.ID,  
                      ProfessorName = (from l in c.Leturers   
                                       where l.Is_Professor   
                                       select l.LastName+" "+l.FirstName).FirstOrDefault(),  
                      AssistantNames = (from l in c.Leturers   
                                        where !l.Is_Professor   
                                        select l.LastName+" "+l.FirstName)
                                        .ToList()   //hmmm problem
                  };

我使用的 ModelView 是另一個可能的問題原因：

public class CourseView
    {
        public int ID { get; set; }
        public string CourseName { get; set; }
        public string ProfessorName { get; set; }
        public List AssistantNames { get; set; }
    }

嗯助手名稱的字符串列表有問題不是嗎？ 在我的愚蠢結束時，在視圖中，我使用@foreach(var s in item.AssistantNames){@s}遍歷了這個列表
@Ladislav 建議使用IQueryable而不是字符串，如何在哪里？

對於我到目前為止所做的解決方案，我收到以下錯誤：

需要幫忙！

Answer 1

刪除ToList()調用，然后將 Assistants 屬性更改為：

public IQueryable AssistantNames { get; set; }

Answer 2

看看這是否有效

var courseViews = from c in db.Courses
                  let assistantsList =  (from l in c.Leturers   
                                        where !l.Is_Professor   
                                        select l.LastName+" "+l.FirstName).ToList()   
                  select new CourseView()  
                  {  
                      CourseID = c.ID,  
                      ProfessorName = (from l in c.Leturers   
                                       where l.Is_Professor   
                                       select l.LastName+" "+l.FirstName).FirstOrDefault(),  
                      AssistantNames =  assistantsList
                  };

Answer 3

另一種方法是，因為您無論如何都要物化所有課程，將查詢分成兩部分，第一個物化數據，第二個使用它來創建課程視圖（現在是 Linq 到對象查詢）：

var courses = (from c in db.Courses 
               select new { c.ID, Leturers = c.Leturers.ToList() }).ToList();

var courseViews = from c in courses 
                  select new CourseView()  
                  {  
                      CourseID = c.ID,  
                      ProfessorName = (from l in c.Leturers   
                                       where l.Is_Professor   
                                       select l.LastName+" "+l.FirstName).FirstOrDefault(),  
                      AssistantNames = (from l in c.Leturers   
                                        where !l.Is_Professor   
                                        select l.LastName+" "+l.FirstName)
                                        .ToList()  
                  };