Group By Sum Linq to SQL in C# - sql

Question

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.
I have a view in my database called view_ProjectTimeSummary, this has the following fields:
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<>:
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:
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 sum of the field double_Hours for that user and project between the to and from date parameters (and not separate entries for each date)?
e.g. a List<> with the following fields:
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)?
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?
Thanks
Steve

Answer 1

Start out by defining a class to hold the result:
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.
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)
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();