Question

I have a somewhat simple query in SQL that I would like to convert to Linq to Entities.

Basically, I want all of the available courses in the database, but I want the last test result for each course for a specific user if they have taken the course. They may have taken a course multiple times, but I would only want the last test result for each test. Is this possible with one Linq statement?

Here is the SQL:

select c.courseid, c.Name, ca.result
from Course c
    left join CourseAttempt ca
    on c.CourseId = ca.CourseId
        and ca.CourseAttemptId in
        (
            select max(courseattemptid)
            from courseattempt
            where userid=1234
            group by courseid
        )

Here is what I have so far:

var stuff = (from c in context.Course
             join ca in context.CourseAttempt.Where(a => a.userid == _userid) 
             on c.CourseId equals ca.Course.CourseId into jca
             select new
             {
                 courseId = c.CourseId,
                 name = c.Name,
                 result = jca.Select(a => a.result)
             }).ToList();

The problem is that result is an array of all of the results. How do I only get the last result?

Answer 1

This solution works:

var stuff = (from c in context.Course
             join ca in context.CourseAttempt.Where(a => a.user.userid == _userid) 
             on c.CourseId equals ca.Course.CourseId into jca
             select new
             {
                 courseId = c.CourseId,
                 name = c.Name,
                 result = jca.OrderByDescending(a => a.CourseAttemptId).Take(1).Select(a => a.result).Cast<int>().DefaultIfEmpty(-1).FirstOrDefault()                 
             }).ToList();