Question

非常直接，我正在尝试Sum Amount + Adjusted

我确定它不是最好的使用方法。

var a1 = context.Employee.Select( a => a.Amount).ToList().Sum();
var b1 = context.Employee.Select(b => b.Adjusted).ToList().Sum();
var c1 = a1+b1;

Answer 1

无需创建任何列表（如果这是LINQ to SQL或EF，则会从数据库中提取大量数据） - 您可以使用：

var c1 = context.Employee.Sum(x => x.Amount + x.Adjusted);

假设您不需要个人总和。如果你这样做，我可能会使用：

var a1 = context.Employee.Sum(x => x.Amount);
var b1 = context.Employee.Sum(x => x.Adjusted);
var c1 = a1 + b1;

诚然，这是两个电话。这个可以完成Aggregate，但肯定会更加丑陋。

var both = context.Employee.Aggregate(
       new { Amount = 0, Adjusted = 0 }, // Seed
       (pair, emp) => new { pair.Amount + emp.Amount,
                            pair.Adjusted + emp.Adjusted });
var a1 = both.Amount;
var b1 = both.Adjusted;
var c1 = a1 + b1;

Answer 2

除了@Jon Skeet的帖子，还有一些与主题相关的调查。

此处ID的{{1}} int和CustomerID <{1}}

int?

将被翻译为：

Purchases.Sum(p => p.ID + p.CustomerID);

和

SELECT 
    [GroupBy1].[A1] AS [C1]
    FROM ( SELECT 
        SUM([Extent1].[A1]) AS [A1]
        FROM ( SELECT 
            [Extent1].[ID] + [Extent1].[CustomerID] AS [A1]
            FROM [dbo].[Purchase] AS [Extent1]
        )  AS [Extent1]
    )  AS [GroupBy1]

将被翻译为：

Purchases.Sum(p => p.ID + (p.CustomerID ?? 0));

使用Linq（lambda表达式）的多重求和

2 个答案: