使用重复参数优化可枚举的LINQ WHERE语句 [英] Refine Enumerable LINQ WHERE statement with repeated parameters

问题描述

我有以下代码返回在确定的日期内合同到期的所有记录:

I have the following code to return all records that has the contract expiration in determined days:

return pSource
                .Where(q => 
                    q.StaffContracts.OrderByDescending(p => p.SignedDate).FirstOrDefault().Timespan.HasValue &&
                    q.StaffContracts.OrderByDescending(p => p.SignedDate).FirstOrDefault().SignedDate.HasValue &&
                    (q.StaffContracts.OrderByDescending(p => p.SignedDate).FirstOrDefault().SignedDate.Value.AddMonths( q.StaffContracts.OrderByDescending(p => p.SignedDate).FirstOrDefault().Timespan.Value)
                    - now).TotalDays <= value);

如您所见，q.StaffContracts.OrderByDescending(p => p.SignedDate).FirstOrDefault()被重复了很多次.有没有一种方法可以缩短此语句?它的等效SQL语句是什么?

As you can see, q.StaffContracts.OrderByDescending(p => p.SignedDate).FirstOrDefault() is repeated many times. Is there a way to shorten this statement? And what is its equivalence SQL statement?

推荐答案

这种方式怎么样?

return
    from q in pSource
    let sc = q.StaffContracts
        .OrderByDescending(p => p.SignedDate)
        .FirstOrDefault()
    where sc != null
    let ts = sc.Timespan
    let sd = sc.SignedDate
    where ts.HasValue
    where sd.HasValue
    where (sd.Value.AddMonths(ts.Value) - now).TotalDays <= value
    select q;

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