convert sql query to LINQ statement

Question

I am struggling to translate this sql statement to a LINQ statement.

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

this is what I got so far, but I could be completely wrong as I am very new to writing LINQ statements

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

the SQL query does give me results I'm looking for.

Answer 1

Your sql query can be translated this way:

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);

Update

If you are using Entity Framework, this query could be easier if you use navigation properties instead joins. Seeing your sql query I notice you have a many to many relationship between Researchers and Submissions . Supposing you have a model like this:

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;}
}

Your query would be:

 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);

The solution I show above is mapping the junction table ( ResearcherSubmissions ), but if that table only consists of the foreign keys and no other columns, then that table can be abstracted by EF and the two sides get a navigational property exposing a collection of the other side (check this link if you want to learn more about that subject):

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;}
}

And your query could be this way:

 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);