Convert T-SQL into LINQ Lambda

Question

How can i write this query in LINQ lambda expression or query syntax if required? I have been trying for a while now. The multiple joins are making it difficult. The total records on the join are over 2000 and the final result should be about 15 records

select 
    year([date]), 
    month([date]),
    sum(ot.rate)
from s as s 
join cs cs on cs.s_id= s.id
join ot ot on ot.id = cs.o_id
group by
    year([date]), 
    month([date])

this is the closest I have got but will not compile. I cannot access the ot property from within the select block.

    var query = from se in table_se
        join cs in table_cs on se.Id equals cs.S_Id
        join ot in table_ot on cs.O_Id equals ot.Id
        group se by new { se.Date.Year, se.Date.Month } into grp 
        select new
        {
            grp.Key.Year,
            grp.Key.Month,
            grp.Sum(ot.Rate)
        };

Answer 1

你非常接近 - Enumerable.Sum采取谓词

var query = from se in table_se
        join cs in table_cs on se.Id equals cs.S_Id
        join ot in table_ot on cs.O_Id equals ot.Id
        group ot by new { se.Date.Year, se.Date.Month } into grp 
        select new
        {
            Year = grp.Key.Year,
            Month = grp.Key.Month,
            Sum = grp.Sum(x => x.Rate)
        };