EF Core Linq 上子查询的总和

Question

我想通过在求和查询中输入子查询来获得结果。

当我写入 Sql 时，以下代码有效。

但是在 EF 上，如何在顶部添加另一个选择？

SQL

这段代码是工作。

select 
    sum (data.rate)
from 
(
    SELECT 
        t1.Id,
        (c.rate / 
        (SELECT COUNT(1) FROM [table4] AS [t4] WHERE ([t4].[FKId] = p1.Id))) as rate        
FROM [table1] AS [t1]
INNER JOIN [table2] AS [t2] ON ([t1].[FKId] = [t2].[Id])
INNER JOIN [table3] AS [t3] ON ([t1].[FKId] = [t3].[Id]))
as data

C＃

var data = await (
    ????
    from t1 in ctx.table1
    join t2 in ctx.table2 on new { t1.FKId} equals new { FKId = t2.Id}
    join t3 in ctx.table3 on new { t1.FKId} equals new { FKId = t3.Id}
    select new
    {
        rate = t3.Rate /
            (from t4 in ctx.table4
             where  t4.FKId == t2.Id
             select t4.Id)
            .Count())
     })
     .SumAsync(sm => (double?)sm.rate ?? 0);

此 C# 代码不起作用。

错误：

无法对包含聚合或子查询的表达式执行聚合函数。

Answer 1

根据这个答案，EF Core 3.0 仍然无法处理这种情况（！）。

但是，您可以在没有子查询的情况下转换查询（有效地，使用SelectMany）并且它应该可以工作：

var ans = await (from t1 in ctx.table1
                 join t2 in ctx.table2 on t1.FKId equals t2.Id
                 join t3 in ctx.table3 on t1.FKId equals t3.Id
                 from t4 in ctx.table4
                 where t4.FkId == t2.Id
                 group t4.Id by new { t3.rate, t2.Id } into t2g
                 select t2g.Key.rate / t2g.Count()
                )
                .SumAsync();