Linq加入三個表

我有三個表，需要編寫一個linq查詢，它基於兩個不同的聯接從所有活動中提取。Linq加入三個表

我需要在志願者中ActivityVolunteers
我需要的所有活動，其中OrganizationID是在活動表和志願屬於organizaiton（OrganizationVolunteers），但不存在ActivityVolunteers活動。志願者可能不屬於該活動，但屬於組織。

下面是我在編寫Linq時的表格結構。

活動

ActivityID
ActivityName
OrganizationID

ActivityVolunteers

ActivityID
VolunteerID
ActivityRole

OrganizationVolunteers

OrganizationID
VolunteerID

這是我在LINQ兩掌，我想不通加入兩個結果集只得到了獨特的活動。

from a in Activities 
join av in ActivityVolunteers on a.ActivityID equals av.ActivityID 
where av.VolunteerID==1 
select new 
    { 
     a.ActivityID, 
     a.ActivityName, 
     av.ActivityRole, 
     a.OrganizationID 
    } 

from org in (from a in Activities 
join ov in OrganizationVolunteers on a.OrganizationID equals ov.OrganizationID 
where ov.VolunteerID==1 
select new 
    { 
     a.ActivityID, 
     a.ActivityName, 
     ActivityRole = "Prospect", 
     a.OrganizationID 
    }) 
select org

我試過一個工會，但它是複製記錄。

(from a in Activities 
join av in ActivityVolunteers on a.ActivityID equals av.ActivityID 
where av.VolunteerID==1 
select new 
    { 
     a.ActivityID, 
     a.ActivityName, 
     av.ActivityRole, 
     a.OrganizationID, 
     OrganizationName = (from o in Organizations where o.OrganizationID == a.OrganizationID select o.OrganizationName).FirstOrDefault() 
    }).Union 
    (from a in Activities 
join ov in OrganizationVolunteers on a.OrganizationID equals ov.OrganizationID 
where ov.VolunteerID==1 
select new 
    { 
     a.ActivityID, 
     a.ActivityName, 
     ActivityRole = "Prospect", 
     a.OrganizationID, 
     OrganizationName = (from o in Organizations where o.OrganizationID == a.OrganizationID select o.OrganizationName).FirstOrDefault() 
    })

來源

2010-07-19 scottrakes

我想我正在尋找一個只提供不同的聯盟。 – scottrakes 2010-07-19 20:12:19

'聯合'提供了獨特的答案... – 2010-07-19 20:30:10

這可能是有用的：http://stackoverflow.com/questions/8900077/linq-join-3-tables-with-or-condition/10784347#10784347 – Prasanna 2012-05-28 12:11:47

(from a in Activities 
join ov in OrganizationVolunteers on a.OrganizationID equals ov.OrganizationID 
join av in ActivityVolunteers 
on a.ActivityID equals av.VolunteerID into JoinedActVol 
from av in JoinedActVol.DefaultIfEmpty() 
where ov.VolunteerID==1 
select new 
    { 
     a.ActivityID, 
     a.ActivityName, 
     av.ActivityRole, 
     a.OrganizationID, 
     OrganizationName = (from o in Organizations where o.OrganizationID == a.OrganizationID select o.OrganizationName).FirstOrDefault() 
    }).Union 
    (from a in Activities 
join av in ActivityVolunteers on a.ActivityID equals av.ActivityID 
where av.VolunteerID==1 && a.OrganizationID == null 
select new 
    { 
     a.ActivityID, 
     a.ActivityName, 
     av.ActivityRole, 
     a.OrganizationID, 
     OrganizationName = "" 
    })

來源

2010-07-20 00:55:11 scottrakes

Linq加入三個表

回答

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