使用UNION foreach循環中的LINQ to SQL的

Question

在下面的代碼中，我希望retrn n行，但它總是返回零行作爲我的初始設置爲零的記錄。理想情況下，它應該做一個UNION ALL並返回整數列表中的所有整數的記錄clearanceTotals {6,7,8,9,17} 任何想法如何去解決它？

var tbl = (from a in db.Applicants 
    where a.Id == null 
    select new { a.Id, a.Firstname, a.Lastname }); 
    int thisTag; 
    foreach (int c in clearanceTotals) 
    { 
     switch (c) 
     { 
      case 6: 
       thisTag = 38; 
       break; 
      case 8: 
       thisTag = 39; 
       break; 
      case 17: 
       thisTag = 39; 
       break; 
      case 7: 
       thisTag = 42; 
       break; 
      case 9: 
       thisTag = 44; 
       break; 
     } 
     tbl = (from a in db.Applicants 
       join ad in db.ApplicantDeployments on a.Id equals ad.ApplicantId 
       join aa in db.ApplicantAttachments on a.Id equals aa.ApplicantId 
       where a.Nationality == 15 && a.DoNotUse == false && a.ClearanceStatus == c 
       && aa.Tag == thisTag 
       select new { a.Id, a.Firstname, a.Lastname }).Union(tbl); 
    } 

Answer 1

OK，所以我得到這個工作，但它的附加代碼加額外的變量

var temp = (from a in db.Applicants 
where a.Id == null 
select a.Id).ToList(); 

int thisTag; 
foreach (int c in clearanceTotals) 
{ 
    switch (c) 
    { 
     case 6: 
      thisTag = 38; 
      break; 
     case 8: 
      thisTag = 39; 
      break; 
     case 17: 
      thisTag = 39; 
      break; 
     case 7: 
      thisTag = 42; 
      break; 
     case 9: 
      thisTag = 44; 
      break; 
    } 
    temp = temp.Union(from a in db.Applicants 
      join ad in db.ApplicantDeployments on a.Id equals ad.ApplicantId 
      join aa in db.ApplicantAttachments on a.Id equals aa.ApplicantId 
      where a.Nationality == 15 && a.DoNotUse == false && a.ClearanceStatus == c 
      && aa.Tag == thisTag 
      select a.Id).ToList(); 
} 
var tbl = (from a in db.Applicants 
         join ad in db.ApplicantDeployments on a.Id equals ad.ApplicantId 
         where temp.Contains(a.Id) 
         select new { a.Id, a.Firstname, a.Lastname }).Distinct(); 

Answer 2

我認爲問題是，你捕捉在查詢循環變量（c），因此執行查詢時，它僅使用C的最新值。嘗試複製C將循環內的變量：

foreach (int c in clearanceTotals) 
{ 
    int c2 = c; 
    ... 

     ... 
     where a.Nationality == 15 && a.DoNotUse == false && a.ClearanceStatus == c2 
     ...