嘗試將 linq 數據分配到 DTO class 時出錯

Question

我需要將 Linq 數據分配到我的 DTO class 中，但是這個 Linq 查詢得到了這個錯誤。

LINQ to Entities does not recognize the method 'System.String ToString(System.String, System.IFormatProvider)' method, and this method cannot be translated into a store expression. 

我刪除了 int 轉換以避免錯誤，然后我得到了這個錯誤

join 子句中的表達式之一的類型不正確。 類型推斷在加入呼叫中失敗

我的代碼如下，

public class TextDto
{
    public string AddedData { get; set; }
    public string AddedTime { get; set; }
    public string Sender { get; set; }
    public string Name { get; set; }
    public string Messsage { get; set; }
}

linq代碼，

var allText = from nm in context.NotificationMessages
join u in context.Users on new {
    Sender = (int) nm.Sender
}
equals new {
    Sender = u.UserId
}
select new {
    nm.Id,
    nm.AddedTime,
    nm.Lobby.Branch.BranchName,
    u.FirstName,
    u.LastName,
    nm.Message
};

var allTextList = allText.Select(data = >new TextOnDemandDto {

    AddedTime = data.AddedTime.ToString("hh:mm tt", CultureInfo.InvariantCulture),
    Messsage = data.Message,
    Name = data.FirstName + " " + data.LastName

}).ToList();

這個sql，我把它轉換成linq

SELECT nm.id,
       nm.addedtime,
       b.branchname,
       u.firstname,
       u.lastname,
       nm.message
FROM   notificationmessage nm
       INNER JOIN lobby l
               ON l.lobbyid = nm.fklobbyid
       INNER JOIN branch b
               ON b.branchid = l.fkbranchid
       INNER JOIN [user] u
               ON nm.sender = u.userid  

Answer 1

嘗試將您的查詢更改為：

var allText = (from nm in context.NotificationMessages
join u in context.Users 
on nm.Sender equals  u.UserId into ug
 from u in ug.DefaultIfEmpty()
join l in context.Lobbys 
 on    nm.fklobbyid eguals  l.lobbyid into lg
 from l in lg.DefaultIfEmpty()
 join b in  context.Branches 
  on l.fkbranchid  equals b.branchid into bg
 from b in bg.DefaultIfEmpty()
select new {
    nm.Id,
    nm.AddedTime,
    b.BranchName,
    u.FirstName,
    u.LastName,
    nm.Message
}).ToList();

更新：

要獲取 FKNotificationMessageTypeId = 3 的記錄，請在“from b..”和“select”之間插入 where 子句：

... from b ...
where nm.FKNotificationMessageTypeId == 3
select new ....