Question

请帮我将下面的MSSQL转换为LINQ。

SELECT A.id, A.type, COUNT(IIf(B.BookId IS NOT NULL, 0, null)) AS TotalCount
FROM Store A
LEFT JOIN Book B ON A.id = B.id
GROUP BY A.id, A.type;

我目前有这个LINQ代码：

from a in Store
join b in Book on a.id equals b.id into c
from d in c.DefaultIfEmpty()
group a by new
{
    a.id,
    a.type
} into g 
select new
{
    StoreId = g.Key.id,
    StoreType = g.Key.type,
    TotalCount = g.Key !=null?g.Count():0
}

我想我错过了一些重要的事情。

Answer 1

由于您没有尝试从联接的Book部分提取任何值，因此您不需要DefaultIfEmpty()，并且因为联接是“组加入”，因此into子句，您不需要再次分组：

from a in Store
join b in Book on a.id equals b.id into c
select new
{
    StoreId = a.id,
    StoreType = a.type,
    TotalCount = C.Count()
}

转换计数...分组从SQL查询到LINQ

1 个答案: