在 C# 中按总和 Linq to SQL 分组
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Group By Sum Linq to SQL in C#
提问by vitalsigns.sa
Really stuck with Linq to SQL grouping and summing, have searched everywhere but I don't understand enough to apply other solutions to my own.
真的坚持使用 Linq to SQL 分组和求和，到处搜索，但我不明白将其他解决方案应用于我自己的解决方案。
I have a view in my database called view_ProjectTimeSummary, this has the following fields:
我的数据库中有一个名为 view_ProjectTimeSummary 的视图，它具有以下字段：
string_UserDescription
string_ProjectDescription
datetime_Date
double_Hours
I have a method which accepts a to and from date parameter and first creates this List<>:
我有一个方法，它接受一个 to 和 from 日期参数并首先创建这个 List<>：
List<view_UserTimeSummary> view_UserTimeSummaryToReturn =
(from linqtable_UserTimeSummaryView
in datacontext_UserTimeSummary.GetTable<view_UserTimeSummary>()
where linqtable_UserTimeSummaryView.datetime_Week <= datetime_To
&& linqtable_UserTimeSummaryView.datetime_Week >= datetime_From
select linqtable_UserTimeSummaryView).ToList<view_UserTimeSummary>();
Before returning the List (to be used as a datasource for a datagridview) I filter the string_UserDescription field using a parameter of the same name:
在返回列表（用作 datagridview 的数据源）之前，我使用同名参数过滤 string_UserDescription 字段：
if (string_UserDescription != "")
{
view_UserTimeSummaryToReturn =
(from c in view_UserTimeSummaryToReturn
where c.string_UserDescription == string_UserDescription
select c).ToList<view_UserTimeSummary>();
}
return view_UserTimeSummaryToReturn;
How do I manipulate the resulting List<> to show the sumof the field double_Hours for that user and project between the to and from date parameters (and not separate entries for each date)?
我如何操作生成的 List<> 以显示该用户和项目之间的字段 double_Hours的总和（而不是每个日期的单独条目）？
e.g. a List<> with the following fields:
例如具有以下字段的 List<>：
string_UserDescription
string_ProjectDescription
double_SumOfHoursBetweenToAndFromDate
Am I right that this would mean I would have to return a different type of List<> (since it has less fields than the view_UserTimeSummary)?
我是否正确，这意味着我必须返回不同类型的 List<> （因为它的字段少于 view_UserTimeSummary）？
I have read that to get the sum it's something like 'group / by / into b' but don't understand how this syntax works from looking at other solutions... Can someone please help me?
我已经读过它来获得总和，它类似于“group/by/intob”，但从查看其他解决方案时不明白这种语法是如何工作的......有人可以帮助我吗？
Thanks Steve
谢谢史蒂夫
回答by Amy B
Start out by defining a class to hold the result:
首先定义一个类来保存结果：
public class GroupedRow
{
public string UserDescription {get;set;}
public string ProjectDescription {get;set;}
public double SumOfHoursBetweenToAndFromDate {get;set;}
}
Since you've already applied filtering, the only thing left to do is group.
由于您已经应用了过滤，剩下要做的就是分组。
List<GroupedRow> result =
(
from row in source
group row by new { row.UserDescription, row.ProjectDescription } into g
select new GroupedRow()
{
UserDescription = g.Key.UserDescription,
ProjectDescription = g.Key.ProjectDescription,
SumOfHoursBetweenToAndFromDate = g.Sum(x => x.Hours)
}
).ToList();
(or the other syntax)
（或其他语法）
List<GroupedRow> result = source
.GroupBy(row => new {row.UserDescription, row.ProjectDescription })
.Select(g => new GroupedRow()
{
UserDescription = g.Key.UserDescription,
ProjectDescription = g.Key.ProjectDescription,
SumOfHoursBetweenToAndFromDate = g.Sum(x => x.Hours)
})
.ToList();
