c# - LINQ-左联接，分组依据和计数

假设我有以下SQL:

SELECT p.ParentId, COUNT(c.ChildId)
FROM ParentTable p
  LEFT OUTER JOIN ChildTable c ON p.ParentId = c.ChildParentId
GROUP BY p.ParentId

如何将其转换为LINQ to SQL？我被困在COUNT(c.ChildId)，生成的SQL似乎总是输出COUNT(*)。这是到目前为止我得到的:

from p in context.ParentTable
join c in context.ChildTable on p.ParentId equals c.ChildParentId into j1
from j2 in j1.DefaultIfEmpty()
group j2 by p.ParentId into grouped
select new { ParentId = grouped.Key, Count = grouped.Count() }

谢谢!

最佳答案

from p in context.ParentTable
join c in context.ChildTable on p.ParentId equals c.ChildParentId into j1
from j2 in j1.DefaultIfEmpty()
group j2 by p.ParentId into grouped
select new { ParentId = grouped.Key, Count = grouped.Count(t=>t.ChildId != null) }

关于c# - LINQ-左联接，分组依据和计数，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/695506/