Linq Group by / Distinct with Join table

Question

我计划连接2个表，并获得语言列的唯一值。我应该如何实现在Linq?我试着添加"group"，但没有成功。此外，我还想选择s值和r不同的语言值。

我代码:

 public ActionResult QuestionLink(int Survey_ID)
        {
            var query = from r in db.SURV_Question_Ext_Model
                        join s in db.SURV_Question_Model
                        on r.Qext_Question_ID equals s.Question_ID
                        where s.Question_Survey_ID == Survey_ID
                        group r.language << this is not work **
                        select r;
            return PartialView(query.ToList());
        } 

Answer 1

这就是MoreLinq中所谓的DistinctBy。但是如果这个方法在IEnumerable上工作，那么你就不能在EF查询中使用它。但是您可以使用相同的方法:

var query = from r in db.SURV_Question_Ext_Model
            join s in db.SURV_Question_Model on r.Qext_Question_ID equals s.Question_ID
            where s.Question_Survey_ID == Survey_ID
            group new { r, s } by r.language into grp
            select grp.FirstOrDefault();

但我想知道这是不是你想要的。结果取决于数据库碰巧返回的语言的顺序。我认为您应该为特定语言添加谓词并删除分组:

var query = from r in db.SURV_Question_Ext_Model
            join s in db.SURV_Question_Model
            on r.Qext_Question_ID equals s.Question_ID
            where s.Question_Survey_ID == Survey_ID
               && r.language == someVariable
            select new { r, s };

Answer 2

你可以这样做:

var query = from r in db.SURV_Question_Ext_Model
                        join s in db.SURV_Question_Model
                        on r.Qext_Question_ID equals s.Question_ID
                        where s.Question_Survey_ID == Survey_ID
                        group new {r, s} by r.language into rg
                        select rg.Key;