Linq加入三张桌子

2019年8月1日 196次阅读

我有三个表,需要编写一个
linq查询,该查询基于两个不同的连接从所有活动中提取.

>我需要在ActivityVolunteers中存在志愿者的所有活动
>我需要所有活动,其中OrganizationID在Activity表中,志愿者属于组织(OrganizationVolunteers),但不属于ActivityVolunteers.志愿者可能不属于该活动但属于组织.

下面是我尝试编写Linq时的表结构.

活动

> ActivityID
> ActivityName
> OrganizationID

ActivityVolunteers

> ActivityID
>志愿者ID
> ActivityRole

OrganizationVolunteers

> OrganizationID
>志愿者ID

这是我对linq的弱尝试,我无法弄清楚加入两个结果集只能获得独特的活动.

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

我尝试了一个联盟,但它重复了记录.

(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()
    })

最佳答案

(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 = ""
    })
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