c# - 在 LINQ 中选择计数

Question

我有一个带有列的 SQL Server 表ResolvedDate和ResolvedBy.

现在我想选择这两列并计算它们的结果，我想我会这样实现：

_dataContext.Activities
    .Where(a => a.IsResolved && a.ResolvedBy == userId)
    .Select(a => new { a.ResolvedDate, ***COUNT*** });

如您所见，缺少 Count-Part。

我想得到在这个 ResolvedDate 中完成的每一个活动并计算它。

我该如何实施？

Answer 1

from a in dataContext.Activities
where a.IsResolved && a.ResolvedBy == userId
group a by a.ResolvedDate into g
select new {ResolvedOn=g.Key, NumberResolved= g.Count()}

Answer 2

如果您尝试按日期计算每个项目，则需要使用GroupBy：

var countsByDate = _dateContext.Activities
                           .Where(a => a.IsResolved && a.ResolvedBy == userId)
                           .GroupBy(a => a.ResolvedDate)
                           .Select(g => new {ResolvedDate = g.Key, Count = g.Count() });

Answer 3

您必须按 ResolvedDate 对数据进行分组，以获取每天解决的活动数量。

var dates = from a in dataContext.Activities
            where a.IsResolved && a.ResolvedBy == userId
            group a by a.ResolvedDate into g
            select new { Date = g.Key, Count = g.Count() }

要按天分组（不包括小时、分钟等），您可以更改 group 语句：

var dates = from a in dataContext.Activities
            where a.IsResolved && a.ResolvedBy == userId
            group a by a.ResolvedDate.Date into g
            select new { Date = g.Key, Count = g.Count() }

Answer 4

var dates = dataContext.Activities
    .Where(a => a.IsResolved && a.ResolvedBy == userId)
    .Select(a => a.ResolvedDate)
    .ToList();

var count = dates.Count;

如果您只想获取计数，则可以通过单独选择计数来使其更快：

var count = dataContext.Activities
    .Count(a => a.IsResolved && a.ResolvedBy == userId);