LINQ中的多个JOIN + SUM（）查询 - ＆gt;无法在视图中循环

Question

我正在尝试将SQL查询转换为LINQ，但经过多次尝试后，我仍然不在那里......有人可以帮忙吗？

这是我正在使用的SQL语句

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

这是我到目前为止所提出的，但它缺少一个sum（），其中我硬编码数字3，应该是Skills.level的总和：

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();

视图包出现以下错误（无法找到电子邮件，而在下面的变量中，您可以看到它们确实存在...）：

感谢您帮助我！

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)

如果您在实体上设置了导航属性，则会更简单一些：

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)

或者，使用查询语法

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) }

要按总额订购，您可以这样做：

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