c# - C# Linq：添加另一个连接条件

Question

我有一个查询：

// Query: gets recipients that have not been sent yet....
var query = (from rec in ent.Recipients 
join ch in ent.CampaignHistories on rec.RecipientID equals ch.RecipientID
into chl
from x in chl.DefaultIfEmpty().Where(xx => !xx.RecipientID.HasValue)

select new BRecipient()  
 {
   Email = rec.Email,
   Name = rec.Name,
   RecipientID = rec.RecipientID
 }).Take(remaining);

这基本上会在 SQL 中进行左连接，相当于：

Select * FROM            Recipients AS R LEFT OUTER JOIN
                         CampaignHistory AS H ON R.RecipientID = H.RecipientID 
WHERE        (H.RecipientID IS NULL)

我想要的是：

Select * FROM            Recipients AS R LEFT OUTER JOIN
                             CampaignHistory AS H ON R.RecipientID = H.RecipientID
AND H.CampaignID <> 21 
    WHERE        (H.RecipientID IS NULL)

如何创建 LINQ？

Answer 1

我相信会是：

join ch in ent.CampaignHistories.Where(x=>x.CampaignID != 21)
    on rec.RecipientID equals ch.RecipientID

但老实说，我看不出你在做什么。你为什么不简单地做：

from rec in ent.Recipients
where !ent.CampaignHistories
          .Any(x=>x.RecipientID == rec.RecipientID && x.CampaignID != 21)
select ...

Answer 2

var query = (from rec in ent.Recipients
             join ch in ent.CampaignHistories.Where(xx => !xx.RecipientID.HasValue && xx.CampaignID != 21) on rec.RecipientID equals ch.RecipientID
             into chl
             from x in chl.DefaultIfEmpty()

             select new BRecipient()
             {
                 Email = rec.Email,
                 Name = rec.Name,
                 RecipientID = rec.RecipientID
             }).Take(remaining);