对LINQ转换的SQL查询（LEFT JOIN和NULL值）

Question

我试图将SQL查询“转换”为LINQ，直到现在没有成功。

这是我的SQL查询，返回一个结果与空值几列（正确的输出）：

SELECT patient.idPatient, removed, fat.status AS FATstatus, fad.status AS FADstatus, 
fa.status AS FAstatus, fdv.status AS FDVstatus, ffu.status AS FFUstatus, fmbct.status 
AS FMBCTstatus, fnt.status AS FNTstatus, fs.status AS FSstatus, ftd.status AS FTDstatus 
FROM patient 
LEFT JOIN FormAdjuvantTreatment fat ON patient.idPatient = fat.idPatient 
LEFT JOIN FormAdvancedDisease fad ON patient.idPatient = fad.idPatient 
LEFT JOIN FormAnamnesis fa ON patient.idPatient = fa.idPatient 
LEFT JOIN FormDemoVariables fdv ON patient.idPatient = fdv.idPatient 
LEFT JOIN FormFollowUp ffu ON patient.idPatient = ffu.idPatient 
LEFT JOIN FormMBCTreatment fmbct ON patient.idPatient = fmbct.idPatient 
LEFT JOIN FormNeoadjuvantTreatment fnt ON patient.idPatient = fnt.idPatient 
LEFT JOIN FormSurgery fs ON patient.idPatient = fs.idPatient 
LEFT JOIN FormTumorDisease ftd ON patient.idPatient = ftd.idPatient 
WHERE patient.idResearcher = '01-01'; 

这是我翻译的LINQ查询。我不返回任何结果（不正确的输出）：

var query = (from u in db.Patients.DefaultIfEmpty() 
join fat in db.FormAdjuvantTreatments on u.idPatient equals fat.idPatient 
join fad in db.FormAdvancedDiseases on u.idPatient equals fad.idPatient 
join fa in db.FormAnamnesis on u.idPatient equals fa.idPatient 
join fdv in db.FormDemoVariables on u.idPatient equals fdv.idPatient 
join ffu in db.FormFollowUps on u.idPatient equals ffu.idPatient 
join fmbct in db.FormMBCTreatments on u.idPatient equals fmbct.idPatient 
join fnt in db.FormNeoadjuvantTreatments on u.idPatient equals fnt.idPatient 
join fs in db.FormSurgeries on u.idPatient equals fs.idPatient 
join ftd in db.FormTumorDiseases on u.idPatient equals ftd.idPatient 
where u.idResearcher == idResearcher 
select new 
{ 
    u.idPatient, 
    u.removed, 
    FormAdjuvantTreatment = (fat.status == null ? "NULL" : fat.status), 
    FormAdvancedDisease = (fad.status == null ? "NULL" : fad.status), 
    FormAnamnesi = (fa.status == null ? "NULL" : fa.status), 
    FormDemoVariable = (fdv.status == null ? "NULL" : fdv.status), 
    FormFollowUp = (ffu.status == null ? "NULL" : ffu.status), 
    FormMBCTreatment = (fmbct.status == null ? "NULL" : fmbct.status), 
    FormNeoadjuvantTreatment = (fnt.status == null ? "NULL" : fnt.status), 
    FormSurgery = (fs.status == null ? "NULL" : fs.status), 
    FormTumorDisease = (ftd.status == null ? "NULL" : ftd.status), 
}).ToList(); 

Answer 1

这个MSDN链接demonstraes如何编写LEFT OUTER JOINS in LINQ：

Answer 2

感谢@lazyberezovsky和@彼得 - Geerkens我已经解决了我的问题。

SQL查询（内左连接）：

SELECT patient.idPatient, removed, fat.status AS FATstatus 
FROM patient 
LEFT JOIN FormAdjuvantTreatment fat ON patient.idPatient = fat.idPatient 
WHERE patient.idResearcher = '01-01'; 

翻译正确的LINQ查询（内左连接）：

var query = (from u in db.Patients.DefaultIfEmpty() 
join fat in db.FormAdjuvantTreatments on u.idPatient equals fat.idPatient into JoinedPatientFAT 
from fat in JoinedPatientFAT.DefaultIfEmpty() 
where u.idResearcher == idResearcher 
select new 
{ 
u.idPatient, 
u.removed, 
FormAdjuvantTreatment = fat.status ?? "NULL" 
} 
).ToList();