從 linq (linq2db) 中的另一個列表中排除一個列表

Question

我正在通過 linq2db 從數據庫中進行兩次提取。 我有兩個列表 TaskDone 和 TaskNotAccomplished。 我想擁有不在 TaskDone List 中的行

 taskDone = from t in db.tblTasks join a in db.tblTaskResult on t.TaskId equals a.TaskId 
            where 
            a.UserId == tUserId
            select new taskDone 
            {
                TaskId = t.TaskId.ToString(),
                Subject = t.Subject
            }).ToList());

 taskNotAccomplished= from t in db.tblTasks  where 
               t.IsActive == true 
               select new TaskNotAccomplished
               {
                   TaskId = t.TaskId .ToString(),
                   Subject= t.Subject,                                                                       
                   EndDate = t.DateTaskEnd,                                                                      
                   TaskTime= t.TaskTime,
               }).ToList());

如何不獲取 taskDone (TaskId) List 中的行？

Answer 1

您可以創建一個 taskDone Id 列表：

var taskDoneIdLst = (from x in taskDone select x.TaskId).ToList();

如果數據庫中的 TaskId 是 integer 列，您必須：

var taskDoneIdLst = (from x in taskDone select Convert.ToInt64(x.TaskId)).ToList();

然后在 taskNotAccomplished 查詢中按 (&&.taskDoneLst.Contains(t:TaskId)) 過濾它：

taskNotAccomplished= from t in db.tblTasks  where 
               t.IsActive == true 
              && !taskDoneLst.Contains(t.TaskId)
               select new TaskNotAccomplished
               {
                   TaskId = t.TaskId .ToString(),
                   Subject= t.Subject,                                                                       
                   EndDate = t.DateTaskEnd,                                                                      
                   TaskTime= t.TaskTime,
               }).ToList());

Answer 2

不確定我是否正確理解了問題，但如果您不將所有內容都放入列表中，您可以通過 LEFT JOIN 來做到這一點。

請注意，我已刪除TaskId.ToString()以避免表掃描：

var taskDoneQuery = 
    from t in db.tblTasks 
    join a in db.tblTaskResult on t.TaskId equals a.TaskId 
    where a.UserId == tUserId
    select new 
    {
        TaskId = t.TaskId,
        Subject = t.Subject
    };
            
var taskNotAccomplished = 
    from t in db.tblTasks 
    where t.IsActive == true 
    from td in taskDoneQuery.LeftJoin(td => td.TaskId == t.TaskId)
    where td == null
    select new TaskNotAccomplished
    {
        TaskId = t.TaskId.ToString(),
        Subject = t.Subject,                                                                       
        EndDate = t.DateTaskEnd,                                                                      
        TaskTime = t.TaskTime,
    };

您還可以加快查詢速度，因為無需兩次加入同一個表。

var taskNotAccomplished = 
    from t in db.tblTasks 
    where t.IsActive == true 
    from a in db.tblTaskResult.LeftJoin(a => a.TaskId == t.TaskId)
    where a == null
    select new TaskNotAccomplished
    {
        TaskId = t.TaskId.ToString(),
        Subject = t.Subject,                                                                       
        EndDate = t.DateTaskEnd,                                                                      
        TaskTime = t.TaskTime,
    };