将Sql转换为Linq（到实体）

我有一个这样的查询，它可以正常工作。如果一个学生得到不止一个过程，它一一列举：将Sql转换为Linq（到实体）

SELECT ks.KullaniciKodu as username, ks.Sifre as password, k.adi as firstname, k.soyadi as lastname, k.Email as email, 
    MAX(CASE WHEN c.DERSKODU = 'ENF100' THEN 'ENF100' ELSE '' END)As course1, 
    MAX(CASE WHEN c.DERSKODU = 'ATA101' THEN 'ATA101' ELSE '' END) As course2, 
    MAX(CASE WHEN c.DERSKODU = 'TDB101' THEN 'TDB101' ELSE '' END) As course3, 
    MAX(CASE WHEN c.DERSKODU = 'İNG101' THEN 'İNG101' ELSE '' END) As course4 
FROM Kayit k 
JOIN DersNotu dn ON dn.KayitNo = k.KayitNo 
JOIN Ders c ON c.DersKayitNo = dn.DersKayitNo AND c.DERSKODU IN ('ENF100','ATA101','TDB101', 'İNG101') AND c.DONEM = '201512' 
JOIN KullaniciSifre ks ON ks.KullaniciKodu = k.KullaniciKodu 
GROUP BY ks.KullaniciKodu, ks.Sifre, k.adi, k.soyadi, k.Email

但是，当我把它转换到LINQ（到实体），它只是变得一门课程或所有课程都为空。这段代码的区别和问题在哪里？

from k in db.Kayit 
join dn in db.DersNotu on k.KayitNo equals dn.KayitNo 
join c in db.Ders on dn.DersKayitNo equals c.DersKayitNo 
join ks in db.KullaniciSifre on k.KullaniciKodu equals ks.KullaniciKodu 
where 
    (new string[] { "ENF100", "ATA101", "TDB101", "İNG101" }).Contains(c.DersKodu) && 
    c.Donem == 201512 
group new { ks, k, c } by new 
{ 
    ks.KullaniciKodu, 
    ks.Sifre, 
    k.Adi, 
    k.Soyadi, 
    k.Email 
    } into g 
select new 
{ 
    KullaniciKodu = g.Key.KullaniciKodu, 
    Sifre = g.Key.Sifre, 
    Adi = g.Key.Adi, 
    Soyadi = g.Key.Soyadi, 
    Email = g.Max(p => (
     p.k.Email == string.Empty ? "NULL" : p.k.Email)), 
    Course1 = g.Max(p => (
     p.c.DersKodu == "ENF100" ? "ENF100,1" : "NULL,1")), 
    Course2 = g.Max(p => (
     p.c.DersKodu == "ATA101" ? "ATA101,1" : "NULL,1")), 
    Course3 = g.Max(p => (
     p.c.DersKodu == "TDB101" ? "TDB101,1" : "NULL,1")), 
    Course4 = g.Max(p => (
     p.c.DersKodu == "İNG101" ? "İNG101,1" : "NULL,1")) 
}

来源

2015-10-20 LacOniC

在SQL中使用MAX只是解决此问题的一种技巧。您不应该明确地将其转换为LINQToEntity。这里的问题是你对字符串使用Max。在你的情况下，NULL,1似乎总是被选为最大，除了TDB101,1。

这里的实际逻辑是如ENF100，如果发现任何一个，项目为"ENF100"，否则项目为"NULL,1"。对其他人也是一样的逻辑。因此，它应该是这样的：

Course1 = g.Any(p => p.c.DersKodu == "ENF100") ? "ENF100,1" : "NULL,1", 
Course2 = g.Any(p => p.c.DersKodu == "ATA101") ? "ATA101,1" : "NULL,1", 
Course3 = g.Any(p => p.c.DersKodu == "TDB101") ? "TDB101,1" : "NULL,1", 
Course4 = g.Any(p => p.c.DersKodu == "İNG101") ? "İNG101,1" : "NULL,1"

另外，Email预计错了，它已经包含在组密钥，所以你可以通过组重点项目是：

Email = g.Key.Email

来源

2015-10-20 08:23:53

大。谢谢。 – LacOniC

将Sql转换为Linq（到实体）

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