带有内部连接的 LINQ SUM：如何获取 TimeSpan 的总和

Question

我一直在尝试使用 LINQ 重写以下 SQL 查询，我设法做到了如下：

SQL

select 
    u.FirstName, 
    u.ExpectedWeeklyHours, 
    sum(t.TimeSpent)  -- SQL DataType is Time(7)

from dbo.Users u 
    inner join 
    dbo.Times t 
    on u.UserID = t.UserId
group by u.FirstName, 
         u.ExpectedWeeklyHours

LINQ

using (var data = new DAL())
{
    var result =
        (from times in data.Times
            join users in data.Users on times.UserId equals users.UserID
            select new
            {
                UserName = users.FirstName + " " + users.LastName, 
                ExpectedHours = users.ExpectedWeeklyHours, 
                WorkHours = times.TimeSpent
            } into x
            group x by new
            {
                UserName = x.UserName,
                ExpectedWorkingHours = x.ExpectedHours
            }
            into g
            select new
            {
                UserName = g.Key.UserName,
                ExpectedWorkingHours = g.Key.ExpectedWorkingHours,
                TotalWorkingHours = g.Sum(i=>i.WorkHours)
            }
            ).ToList();
}

我的问题是 WorkHours 的类型为：TimeSpan，我收到以下（编译时间）错误：

• 无法将 lambda 表达式转换为类型 'System.Linq.Expressions.LambdaExpression' 因为它不是 委托类型 无法将 lambda 表达式转换为委托类型 'System.Func' 因为一些返回类型 块中的不能隐式转换为委托返回 类型 无法将类型“System.TimeSpan”隐式转换为“int”

如果我将 WorkHours 列（属性）替换为任何其他类型的 int、double 或 decimal，则一切正常。只是Linq的SUM函数不支持TimeSpan！

你能帮忙吗，提前谢谢你..

编辑

根据以下 wuzdik 提出的建议，我来到了这个问题的解决方案，我分享它以帮助有需要的人：

 using (var data = new DAL())
{
    var result =
        (from times in data.Times
            join users in data.Users on times.UserId equals users.UserID
            select new
            {
                UserID = users.UserID,
                UserName = users.FirstName + " " + users.LastName,
                ExpectedHours = users.ExpectedWeeklyHours,
                WorkHours = times.TimeSpent
            }
            into x
            group x by new
            {
                UserId = x.UserID,
                UserName = x.UserName,
                ExpectedWorkingHours = x.ExpectedHours
            }).AsEnumerable().ToList();

    var finale = (from p in result
        select new TimeModelDashboard
        {
            UserId = p.Key.UserId,
            UserName = p.Key.UserName,
            ExpectedWorkingHours = p.Key.ExpectedWorkingHours,
            TotalWorkingHours = (decimal) p.Sum(t => t.WorkHours.TotalHours)
        }).ToList();

    return Json(finale);
}

Answer 1

您需要创建新的TimeSpan = 时间跨度的总和

TotalWorkingHours = new TimeSpan(g.Sum(w => w.WorkHours.Ticks));

因为 Sum 并没有超载接受 IEnumerable<TimeSpan>，所以请看这里 IEnumerable.Sum。

编辑：

尝试更快地实现查询，这样new Timespan 将在 Linq 中被调用到对象

var result =
    (from times in data.Times
        join users in data.Users on times.UserId equals users.UserID
        select new
        {
            UserName = users.FirstName + " " + users.LastName, 
            ExpectedHours = users.ExpectedWeeklyHours, 
            WorkHours = times.TimeSpent
        } into x
        group x by new
        {
            UserName = x.UserName,
            ExpectedWorkingHours = x.ExpectedHours
        }
        into g
    ).AsEnumerable().Select(new {
            UserName = g.Key.UserName,
            ExpectedWorkingHours = g.Key.ExpectedWorkingHours,
            TotalWorkingHours = new TimeSpan(g.Sum(w => w.WorkHours.Ticks))
      }.ToList();