linq to sql级联查询出错

[fengxuemofa6]

麻烦大家帮我看看这个Linq有什么错误。。刚学，新手求教，。它直接死循环了，本来有200条数据查询了100W条还在查。
return from a in db.A
from b in db.B
from c in db.C
from d in db.D
join a in db.A on a.StudentId equals B.UserID
join d in db.D on d.GeradeID equals C.VID
join d in db.D on d.SubjectID equals C.VID
select new A_Ext
{
Title = a.Title,
UserName=b.UserName,
GeradeName=c.Name,
SubjectName=c.Name,
ViewCount=a.ViewCount,
ReflashTime=a.ReflashTime,
IsValid=a.IsValid
};

[q107770540]

你这是Cross join了


return from a in db.A
join b in db.B on a.StudentId equals b.UserID
join c in db.C on b.GeradeID equals c.VID
join d in db.D on d.SubjectID equals c.VID
select new A_Ext
{
Title = a.Title,
UserName=b.UserName,
GeradeName=c.Name,
SubjectName=c.Name,
ViewCount=a.ViewCount,
ReflashTime=a.ReflashTime,
IsValid=a.IsValid
};

[快溜]

return from a in db.A
from b in db.B
from c in db.C
from d in db.D
join a in db.B on a.StudentId equals B.UserID
join d in db.C on d.GeradeID equals C.VID
join d in db.C on d.SubjectID equals C.VID

[jiuhexuan]

一个一个加join吧

[快溜]

不对吧a，b和c，d之间没有关联

[fengxuemofa6]

上面2个大神，，哪个是正确得。。

[fengxuemofa6]

对，没关联，我爱罗那个正确？

[Times_ORZ]

[Quote=引用 2 楼 ssp2009 的回复:]

return from a in db.A
from b in db.B
from c in db.C
from d in db.D
join a in db.B on a.StudentId equals B.UserID
join d in db.C on d.GeradeID equals C.VID
join d in db.C on d.Subjec……
[/Quote] + 1

[q107770540]

Try:

return from a in db.A
join b in db.B on a.StudentId equals b.UserID
join d in db.D on new{X=d.GeradeID , Y=d.SubjectID }equals new{X=c.VID,Y=c.VID}
select new A_Ext
{
Title = a.Title,
UserName=b.UserName,
GeradeName=c.Name,
SubjectName=c.Name,
ViewCount=a.ViewCount,
ReflashTime=a.ReflashTime,
IsValid=a.IsValid
};

[快溜]

没关联就会笛卡尔积，产生很多数据，感觉你写的没什么意义

[claymore1114]

一个一个 join 查考 猫哥的