Linq Group by / Distinct with Join table

Question

我打算加入 2 table，并获取语言列的不同值。我应该如何在 Linq 中实现这一点？我尝试添加 'group' 但没有运气。此外，我也想 select s 值和 r 不同的语言值。

我的代码：

 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

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;

Answer 2

这就是 MoreLinq 中所谓的 DistinctBy。但是如果该方法适用于 IEnumerable，那么您不能在 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();

但我想知道这是否真的是您想要的。结果取决于数据库碰巧 return 的语言顺序。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 };

Linq Group by / Distinct with Join table

Linq Group by / Distinct with Join table

linq

join

group-by

distinct