CODEWITHSUNDEEP
c#linqjoingroup-byaggregate
Slinky
Slinky

Reputation: 5832

Join, Group By and Aggregate with LINQ

I am kinda new to LINQ and I am trying to write the SQL below into a LINQ statement. It works except for the aggregate part in the SQL version (COUNT(oec.CourseTitle)), which I cannot figure out how to do that in LINQ. Any help is appreciated. Thanks

SQL 

select 
oec.OnlineEducationCourseId, 
oec.CourseTitle,
COUNT(oec.CourseTitle) as CourseCount
from OnlineEducationRegistration as oer
join OnlineEducationCourse oec on oec.OnlineEducationCourseId = oer.OnlineEducationCourseId
where oer.District='K20'and DateCompleted BETWEEN '2013-01-01' AND '2014-01-01'
group by oec.CourseTitle,oec.OnlineEducationCourseId;

LINQ 

var r = (from oer in db.OnlineEducationRegistrations
         join oec in db.OnlineEducationCourses on oer.OnlineEducationCourseId equals
         oec.OnlineEducationCourseId
         where oer.District == districtId && 
               oer.DateCompleted >= start && 
               oer.DateCompleted <= end
               group new {oer, oec} by new {oec.CourseTitle, oec.OnlineEducationCourseId}).ToList();



        foreach (var item in r)
        {
            var courseId = item.Key.OnlineEducationCourseId;
            var courseTitle = item.Key.CourseTitle;
            // aggregate count goes here


        }

Upvotes: 1

Views: 2204

Answers (1)

juharr
juharr

Reputation: 32266

Basically just

var courseCount = item.Count();

Or you could add it in a select

var r = (from oer in db.OnlineEducationRegistrations
         join oec in db.OnlineEducationCourses on oer.OnlineEducationCourseId equals
         oec.OnlineEducationCourseId
         where oer.District == districtId && 
               oer.DateCompleted >= start && 
               oer.DateCompleted <= end
         group new {oer, oec} by new {oec.CourseTitle, oec.OnlineEducationCourseId} into g
         select new {g.OnlineEducationCourseId, g.CourseTitle, CourseCount = g.Count() }).ToList();



    foreach (var item in r)
    {
        var courseId = item.OnlineEducationCourseId;
        var courseTitle = item.CourseTitle;
        var courseCount = item.CourseCount;
    }

Upvotes: 3

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