Sum on subqueries on EF Core Linq - sql-server

Question

I want to get a result by typing subquery into the sum query.
The following code works when I write to Sql.
But on EF, how do I add another select at the top?
SQL
This code is work.
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);
This c# code is not working.
Error:
Cannot perform an aggregate function on an expression containing an
aggregate or a subquery.

Answer 1

Per this answer, EF Core 3.0 still can't handle this situation (!).
However, you can translate the query without a subquery (effectively, using SelectMany) and it should work:
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();