Question

I’m trying to translate an SQL query into LINQ, but after numerous attempts, I’m still not there… Can anyone help ?

This is my working SQL statement

SELECT        Users.email, SUM(Skills.level) AS SkillLevel
FROM            Skills INNER JOIN
                         SkillsPerUser ON Skills.pk_skill_id = SkillsPerUser.fk_skill_id INNER JOIN
                         Users ON SkillsPerUser.fk_user_id = Users.pk_userid
GROUP BY Users.email
ORDER BY SkillLevel DESC

This is what I came up with so far, but it lacks a sum() where I hard coded the number 3, that should be the sum of Skills.level:

var allSkillsPerUser = from u in dc.Users
                                   join spu in dc.SkillsPerUsers on u.pk_userid equals spu.fk_user_id
                                   join s in dc.Skills on spu.fk_skill_id equals s.pk_skill_id
                                   select new { Email = u.email, Level = s.level } into su
                                   group su by su.Email into gsu
                                   select new { Email = gsu.Key, SkillLevel = gsu.Sum(su => su.Level) };

            ViewBag.spu = allSkillsPerUser.ToList();

The view bag gives the following error (Email can’t be found, while in the variables below you can see that they do exist…):

Answer 1

context.Skills
       .Join(context.SkillsPerUser, s => s.pk_skill_id, spu => spu.fk_skill_id, (s, spu) => new { Skill = s, SkillToUser = spu })
       .Join(context.Users, sspu => sspu.SkillToUser.fk_userId, u => u.pk_userid, (sspu, u) => new { Email = u.Email, SkillLevel = sspu.Skill.level })
       .GroupBy(su => su.Email)
       .Select(g => new { Email = g.Key, SkillLevel= g.Sum(su => su.Level) })
       .OrderByDescending(g => g.SkillLevel)

It’s a bit simpler if you have navigation properties set up on your entities:

context.SkillsPerUser
       .Select(spu => new { Email = spu.User.email, Level = spu.Skill.level }) // guessing at the navigation property names here
       .GroupBy(su => su.Email)
       .Select(g => new { Email = g.Key, SkillLevel = g.Sum(su => su.Level) })
       .OrderByDescending(g => g.SkillLevel)

Or, using the query syntax

from u in dc.Users
join spu in dc.SkillsPerUsers on u.pk_userid equals spu.fk_user_id
join s in dc.Skills on spu.fk_skill_id equals s.pk_skill_id
select new { Email = u.email, Level = s.level } into su
group su by su.Email into gsu
select new { Email = gsu.Key, SkillLevel = gsu.Sum(su => su.Level) }

To order by the sum you can do this:

from u in dc.Users
join spu in dc.SkillsPerUsers on u.pk_userid equals spu.fk_user_id
join s in dc.Skills on spu.fk_skill_id equals s.pk_skill_id
select new { Email = u.email, Level = s.level } into su
group su by su.Email into gsu
select new { Email = gsu.Key, SkillLevel = gsu.Sum(su => su.Level) } into userSkills
orderby userSkills.SkillLevel descending