我有一个用LINQ编写的相当复杂的查询来查询我的数据库。我已经确定我只是从每个实体中撤回相关列，因此查询尽可能简洁，因此LINQ填充的对象也不包含任何不必要的列。
如果我直接对DB执行LINQ查询生成的SQL，那么SQL将在大约4秒内运行。但是，从我的LINQ查询执行此操作大约需要25秒。这25秒的大部分时间都被返回的DB数据写入对象。
在执行这部分操作时，是否有任何有用的技巧可以帮助LINQ / Entity Framework解决？
编辑：
当我在下面的查询中调用ToList（）方法时发生长延迟：
var q1 = from u in etc.Users
where (u.flags & (int)UserFlags.Student) == (int)UserFlags.Student
&& (ariStudents.Contains(u.id) || ariStudents.Count == 0)
&& (from ua in etc.UserAssociations where ua.datasetId == datasetId && ua.userId == u.id && ua.type == (int)UserAssocTypes.EnrolActive select ua).Any()
orderby u.id
select new ElightsRaw2
{
Student = new ElrStudent{StudentId = u.id},
StudentData = (
from sd in etc.StudentDatas
where sd.userId == u.id
&& sd.datasetId == datasetId
select new ElrStudentData { attP = sd.attP, attA = sd.attA, attL = sd.attL }
).FirstOrDefault(),
ElightOverall = (
from els in etc.eLightsStudents
where els.datasetId == datasetId
&& els.userId == u.id
select els
).FirstOrDefault(),
Groups = (
// get all courses and groups for user
from c in etc.Cours
join g in etc.Groups on c.id equals g.courseId
join ua in etc.UserAssociations on g.id equals ua.fkId
where ua.datasetId == datasetId
&& ua.userId == u.id
&& ua.type == (int)UserAssocTypes.EnrolActive
&& (ua.flags & (int)UserAssociationFlags.AssociationDeleted) == 0
&& (c.flags & (int)CourseFlags.Deleted) == 0
select new ElrGroupHolder
{
CourseName = c.name,
GroupName = g.name,
Breakdown = new ElrGroupHolderBreakdown
{
UnitsBelowScoreThresh1 = (
from uus in etc.UserUnitScores
join un in etc.Units on uus.unitId equals un.id
join cu in etc.CourseUnits on un.id equals cu.unitId
where uus.userId == u.id
&& (un.flags & (int)UnitFlags.Deleted) == 0
&& (cu.flags & (int)CourseUnitFlags.NotStarted) == 0
&& cu.courseId == c.id
&& (uus.performance > -1 && uus.performance <= amberThresh)
&& !(from exc in etc.UserAssociations where exc.userId == u.id && exc.fkId == un.id && exc.type == (int)UserAssocTypes.ExcludedUnit select exc).Any() // not excluded from unit
select uus
).Count(),
UnitsBelowScoreThresh2 = (
from uus in etc.UserUnitScores
join un in etc.Units on uus.unitId equals un.id
join cu in etc.CourseUnits on un.id equals cu.unitId
where uus.userId == u.id
&& (un.flags & (int)UnitFlags.Deleted) == 0
&& (cu.flags & (int)CourseUnitFlags.NotStarted) == 0
&& cu.courseId == c.id
&& (uus.performance > -1 && uus.performance <= redThresh)
&& !(from exc in etc.UserAssociations where exc.userId == u.id && exc.fkId == un.id && exc.type == (int)UserAssocTypes.ExcludedUnit select exc).Any() // not excluded from unit
select uus
).Count(),
CfcCount = (
from cfc in etc.CFCs
where cfc.datasetId == datasetId
&& cfc.studentId == u.id
&& cfc.dt > dCfcCutoff
&& cfc.type == (int)CfcTypes.Concern
&& (cfc.flags & (int)CfcFlags.Deleted) == 0
&& (
// only include attendance and behaviour CFCs
(cfc.flags & (int)CfcFlags.Attendance) == (int)CfcFlags.Attendance
|| (cfc.flags & (int)CfcFlags.Behaviour) == (int)CfcFlags.Behaviour
)
select cfc
).Count(),
SrsScores = (
from srs in etc.SRScores
join sr in etc.SubReviews on srs.srId equals sr.id
where sr.datasetId == datasetId
&& (sr.flags & (int)SrFlags.Deleted) == 0
&& (srs.flags & (int)SrsFlags.Deleted) == 0
&& sr.dt > dCfcCutoff
&& sr.userId == u.id
&& sr.courseId == c.id
select new ElrSrScore
{
attainment = srs.attainment,
attitude = srs.attitude,
motivation = srs.motivation,
studyskill = srs.studyskill
}
).ToList(),
ElightEnrolment = (
from ele in etc.eLightsEnrolments
where ele.datasetId == datasetId
&& ele.groupId == g.id
&& ele.userId == u.id
select ele
).FirstOrDefault(),
},
CourseAttendance = (
from a in etc.Attendances
where a.studentId == u.id
&& a.courseId == c.id
&& a.weekNumberId == null
&& a.datasetId == datasetId
select a
).FirstOrDefault()
}
).ToList(),
};
return q1.ToList();
答案 0 :(得分：0)
是的！不久前我遇到了类似的事情。我想出的是在LINQ中使用AsParallel（）函数......但是这有一些注意事项。
以下是关于AsParallel（）的更多阅读，希望这有帮助！
https://msdn.microsoft.com/en-us/library/vstudio/dd413237%28v=vs.100%29.aspx - AsParallel Method
https://msdn.microsoft.com/en-us/library/dd997425%28v=vs.110%29.aspx - 并行查询简介
http://www.dotnetperls.com/asparallel - AsParallel的基本演练