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有時，當我使用LINQ編寫查詢時，如果我在循環中使用它。它的表現變慢。實體框架中的性能
var query1 = from c in db.Classes
where c.TeacherId.Equals(teacherId)
select c;
// AnsweredAssignment Query
var query2 = (from c in db.AnsweredAssignments
where c.AssignmentId == assignmentId && c.Student.Class.TeacherId.Equals(teacherId)
select c).ToArray();
// Tokens Query
var query3 = (from c in db.Tokens
where c.AssignmentId == assignmentId && c.Student.Class.TeacherId.Equals(teacherId)
select c).ToArray();
// OverwrittenScores Query
var query4 = (from os in db.OverwrittenScores
where os.AssignmentId == assignmentId && os.Student.Class.TeacherId.Equals(teacherId)
select os).ToArray();
foreach (var c in query1)
{
foreach (var s in c.Students)
{
var aaItems = (from aa in query2
where aa.StudentId == s.StudentId
select aa).ToArray();
// Generate scores for objectives
var id3 = (from aa in aaItems
where !aa.IsMakeup
orderby aa.Score descending
select aa).FirstOrDefault();
if (id3 != null)
{
var aa3 = (from aa in query2
where aa.AnsweredAssignmentId == id3.AnsweredAssignmentId
select aa).SingleOrDefault();
...
}
var tokens = (from t in query3
where t.StudentId == s.StudentId
select new MonitorByGeneralScoreToAnsweredAssignment(AssignmentStatus.Pending)).ToList();
...
// does exist any overwritten score?
var osItem = query4.Where(os => os.StudentId == s.StudentId).SingleOrDefault();
...
}
// OverwrittenScores Query
var query4 = (from os in db.OverwrittenScores
where os.AssignmentId == assignmentId && os.Student.Class.TeacherId.Equals(teacherId)
select os).ToArray();
我現在正在做的是得到我要使用的記錄，而不是一個接一個在循環內部。這是一個很好的做法嗎？有時候我想，我沒有做一個良好的工作:(
當我有記錄，我已經將它保存到內存中，並使用LINQ to對象（從內存中）我得到記錄。