將SQL查詢轉換為LINQ語句

Question

我正在努力將此sql語句轉換為LINQ語句。

select r.FirstName + ' ' + r.Surname as [Name], count(*) as  [Number of Submissions]
from Researcher r
join ResearcherSubmission rs on r.ResearcherID = rs.ResearcherID
join Submission s on s.SubmissionID = rs.SubmissionID
group by r.FirstName, r.Surname

這是到目前為止的內容，但是由於我對編寫LINQ語句非常陌生，所以我可能完全錯了

from r in Researcher
join rs in ResearcherSubmission on rs.ID equal s in Submission
count s in submission
group by r FirstName + ' ' + Surname

SQL查詢的確給了我想要的結果。

Answer 1

您的sql查詢可以這樣翻譯：

var query= from r in db.Researchers
           join rs in db.ResearcherSubmissions on r.ResearcherID equals rs.ResearcherID
           join s in db.Submissions  on s.SubmissionID equals rs.SubmissionID
           group r by new {r.FirstName, r.Surname} into g
           select new {
                       Name= g.Key.FirstName + ' ' + g.Key.Surname,
                       NumberOfSubmissions= g.Count() 
                      };

return Json(query.ToList(), JsonRequestBehavior.AllowGet);

更新資料

如果您使用的是Entity Framework，那么如果您使用導航屬性而不是聯接，則此查詢可能會更容易。 看到您的sql查詢，我注意到您在Researchers和Submissions之間存在多對多關系。 假設您有一個這樣的模型：

public class Researcher
{
   public Researcher 
   {
     ResearcherSubmissions=new List<ResearcherSubmission>();
   }
   public int ResearcherId{get;set;}
   public string FirstName{get;set;}
   public string Surname{get;set;}
   public virtual ICollection<ResearcherSubmission> ResearcherSubmissions{get;set;}
}

public class ResearcherSubmission
{
    [Key, ForeignKey("Researcher"), Column(Order=1)]
    public int ResearcherId{get;set;}
    [Key, ForeignKey("Submission"), Column(Order=2)]
    public int SubmissionId {get;set;}

    public virtual Researcher Researcher{get;set;}
    public virtual Submission Submission {get;set;}
}

public class Submission
{
   public Submission
   {
     ResearcherSubmissions=new List<ResearcherSubmission>();
   }
   public int SubmissionId{get;set;}

   public virtual ICollection<ResearcherSubmission> ResearcherSubmissions{get;set;}
}

您的查詢將是：

 var query= db.Researchers
              .Where(r=>r.ResearcherSubmissions.Count>0)// Researchers that have submissions
              .Select(r=>new {
                               Name= r.FirstName + ' ' + r.Surname,
                               NumberOfSubmissions= r.ResearcherSubmissions.Count 
                             }
                     );
 return Json(query.ToList(), JsonRequestBehavior.AllowGet);

我上面顯示的解決方案是映射聯結表（ ResearcherSubmissions ），但是如果該表僅由外鍵組成，而沒有其他列，則該表可以由EF進行抽象，並且兩側都將獲得一個導航屬性，從而暴露出該表的集合。另一面（如果您想進一步了解該主題，請查看此鏈接 ）：

public class Researcher
{
   public Researcher 
   {
     Submissions=new List<Submission>();
   }
   public int ResearcherId{get;set;}
   public string FirstName{get;set;}
   public string Surname{get;set;}
   public virtual ICollection<Submission> Submissions{get;set;}
}

public class Submission
{
   public Submission
   {
     Researchers=new List<Researcher>();
   }
   public int SubmissionId{get;set;}

   public virtual ICollection<Researcher> Researchers{get;set;}
}

您的查詢可能是這樣的：

 var query= db.Researchers
              .Where(r=>r.Submissions.Count>0)
              .Select(r=>new {
                               Name= r.FirstName + ' ' + r.Surname,
                               NumberOfSubmissions= r.Submissions.Count 
                             }
                     );
 return Json(query.ToList(), JsonRequestBehavior.AllowGet);