從linq查詢中的不同對象中選擇數據

Question

我還是LINQ的新手，並且遇到了一些麻煩。我認爲這一切都搞砸了，但我有一個模型，其中包含幾個屬性和不同類型的對象（項目）。我收到一個錯誤：無法將類型'AnonymousType＃1'轉換爲'string'。我希望能夠從我的NotificationModel對象中引用的ProjectModel對象中選擇ProjectId和ProjectName。這就是我所擁有的，但這不起作用，我怎樣才能改變這個從ProjectModel對象正確地獲取信息？

通知型號：

public int id { get; set; } 
public int ProjectId { get; set; } 
public string ProjectName { get; set; } 
[StringLength(50)] 
public string CreatedBy { get; set; } 
public Nullable<System.DateTime> CreatedDateTime { get; set; } 
public Nullable<bool> IsDeleted { get; set; 

public virtual ProjectModel Project { get; set; } 

試圖檢索數據：如果你有你的Notification實體導航屬性Project

 var notifications = (from a in db.NotificationsLog 
          where a.CreatedBy == userID 
          orderby a.CreatedDateTime ascending 
          select new NotificationModel 
          { 
           id = a.id, 
           ProjectId = from p in db.Projects 
              select new 
                { 
                 ProjectId = p.ProjectId 
                } 
           ProjectName = from p in db.Projects 
              select new 

                { 
                 ProjectName = p.ProjectName 
                } 
           Notes = a.Notes; 
          }); 

Answer 1

，你可以這樣做：

var notifications = 
    (from a in db.NotificationsLog 
    let p = a.Project 
    where a.CreatedBy == userID 
    orderby a.CreatedDateTime ascending 
    select new NotificationModel 
    { 
     id = a.id, 
     ProjectId = p.Id, 
     ProjectName = p.Name, 
     Project = new ProjectModel 
     { 
      ProjectId = p.Id 
      ProjectName = p.Name 
      Notes = a.Notes; 
     } 
    }); 

Answer 2

var notifications = from a in db.NotificationsLog 
        join p in db.Projects on a.ProjectId equals p.ProjectId 
        where a.CreatedBy == userID 
        select new NotificationModel 
          { 
           id = a.id, 
           ProjectId = p.ProjectId, 
           ProjectName = p.ProjectName, 
           Notes = a.Notes 
          };