C# LINQ中计数的选择

我得到了一个SQL Server表，其中包含列

ResolvedDate

和

ResolvedBy

现在我想选择这两列并计算它们的结果，我想我应该这样实现：

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

如您所见，计数部分缺失

我想得到在这个ResolvedDate中完成的每一项活动，并对其进行计数

我如何实现这一点

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，可以通过单独选择计数来加快计算速度：

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

---

如果您试图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() });

---

您必须按ResolvedDate对数据进行分组，以获得每天解决的活动数

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（不含小时、分钟等），您可以更改组声明：

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() }

---

因此，您希望按resolveddate分组，然后进行计数。我认为OP希望按日期分组，并计数每个组的成员。@SLaks:is

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

等于

从[TableName]中选择count（coulmname），其中（IsResolved=1）和（ResolvedBy=@UserID）

？这很有效，谢谢你-只是还不能接受答案：）遗憾的是，这个解决方案有一个负面的东西：06.04.2012 12:00:00 count 1和06.04.2012 12:00:01 count 1以两个结果结束。我该怎么做才能把一整天都分组？@SeToY将第三行a.ResolvedDate.Date改为g，改为

a组

我忘了提到我正在使用EntityFramework 4。因此，LINQ to EntitiesResolved:group a by EntityFunctions中不支持类型成员“Date”。TruncateTime（a.ResolvedDate）“ResolvedDate”可为Null（当活动未解析时）且System.nullable不包含“Date”的定义

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() }