Linq加入三个表

我有三个表，需要编写一个linq查询，它基于两个不同的联接从所有活动中提取。Linq加入三个表

我需要在志愿者中ActivityVolunteers
我需要的所有活动，其中OrganizationID是在活动表和志愿属于organizaiton（OrganizationVolunteers），但不存在ActivityVolunteers活动。志愿者可能不属于该活动，但属于组织。

下面是我在编写Linq时的表格结构。

活动

ActivityID
ActivityName
OrganizationID

ActivityVolunteers

ActivityID
VolunteerID
ActivityRole

OrganizationVolunteers

OrganizationID
VolunteerID

这是我在LINQ两掌，我想不通加入两个结果集只得到了独特的活动。

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

我试过一个工会，但它是复制记录。

(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() 
    })

来源

2010-07-19 scottrakes

我想我正在寻找一个只提供不同的联盟。 – scottrakes 2010-07-19 20:12:19

'联合'提供了独特的答案... – 2010-07-19 20:30:10

这可能是有用的：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 = "" 
    })

来源

2010-07-20 00:55:11 scottrakes

Linq加入三个表

回答

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