关于c＃：LINQ to SQL – 左外连接具有多个连接条件

LINQ to SQL - Left Outer Join with multiple join conditions

我有以下SQL，我正在尝试将其转换为LINQ：

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SELECT f.value
FROM period as p
LEFT OUTER JOIN facts AS f ON p.id = f.periodid AND f.otherid = 17
WHERE p.companyid = 100

我已经看到了左外部联接的典型实现(即into x from y in x.DefaultIfEmpty()等)，但不确定如何引入其他联接条件(AND f.otherid = 17)

编辑

为什么AND f.otherid = 17条件是联接的一部分而不是在WHERE子句中？因为有些行可能不存在f，我仍然希望包括这些行。如果在联接之后的WHERE子句中应用了该条件，那么我就无法获得所需的行为。

不幸的是：

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from p in context.Periods
join f in context.Facts on p.id equals f.periodid into fg
from fgi in fg.DefaultIfEmpty()
where p.companyid == 100 && fgi.otherid == 17
select f.value

似乎等同于：

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SELECT f.value
FROM period as p
LEFT OUTER JOIN facts AS f ON p.id = f.periodid
WHERE p.companyid = 100 AND f.otherid = 17

这不是我想要的。

相关讨论

另一个有效的选项是将连接分散到多个LINQ子句中，如下所示：

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public static IEnumerable<Announcementboard> GetSiteContent(string pageName, DateTime date)
{
IEnumerable<Announcementboard> content = null;
IEnumerable<Announcementboard> addMoreContent = null;
try
{
content = from c in DB.Announcementboards
//Can be displayed beginning on this date
where c.Displayondate > date.AddDays(-1)
//Doesn't Expire or Expires at future date
&& (c.Displaythrudate == null || c.Displaythrudate > date)
//Content is NOT draft, and IS published
&& c.Isdraft =="N" && c.Publishedon != null
orderby c.Sortorder ascending, c.Heading ascending
select c;

//Get the content specific to page names
if (!string.IsNullOrEmpty(pageName))
{
addMoreContent = from c in content
join p in DB.Announceonpages on c.Announcementid equals p.Announcementid
join s in DB.Apppagenames on p.Apppagenameid equals s.Apppagenameid
where s.Apppageref.ToLower() == pageName.ToLower()
select c;
}

//CROSS-JOIN this content
content = content.Union(addMoreContent);

//Exclude dupes - effectively OUTER JOIN
content = content.Distinct();

return content;
}
catch (MyLovelyException ex)
{
throw ex;
}
}