Compare Array of IDs Entity Framework

Question

I have a simple scenario for which i want to write LINQ query, But i am unable to get it right. Here is the scenario:

I have 3 Tables:

STUDENT:
    --------------------------
    SID   Name
    ---------------------
    1     Jhon
    2     Mishi
    3     Cook
    4     Steven

COURSE:
    -------------------
    CID     Name
    -------------------
    1       Maths
    2       Physics
    3       Bio
    4       CS

STUDENTCOURSE:
    ---------------------------
    SCID   SID   CID
    -----------------------
    1       1     1
    2       1     2
    3       1     4
    4       2     1
    5       2     2
    6       2     3
    7       3     1
    8       3     4
    10      4     2

For this case i want to pass array of course ids to query and return all student those have all the these courses registered against them. What i tried:

 int[] cIds = {1,2,4 };
 var result = from s in context.Students
              where s.StudentCourses.Any(sc=> cIds.Contains(sc.CID))
              select s;

But this returns students those registered either of the course id 1,2,4. Hope you understand my problem.

Thanks for the help.

Answer 1

Use this:

int[] cIds = {1,2,4 };
var q = context.StudentCourses.Join(context.Students, 
                                    x => x.SId, 
                                    x => x.Id, 
                                    (sc, s) => new { Student = s, CourseId = sc.CId })
        .GroupBy(x => x.Student.Id)
        .Where(sc => cIds.All(cid => sc.Any(y => y.CourseId == cid)))
        .Select(x => x.FirstOrDefault().Student)
        .ToList();

Or if you prefer linq query:

int[] cIds = {1,2,4 };
var q2 = (from s in context.Students
          join sc in context.StudentCourses on s.Id equals sc.SId into sCources
          where cIds.All(id => sCources.Any(y => y.CId == id))
          select s).ToList();

Here is a fiddle for it, using linq-to-objects.

Edit:
I didn't notice that in your model there is a navigation property from Student to StudentCourse , in this case the query will be much simpler and does not need join, and Patrick's answer works perfectly.

Answer 2

Try the following:

int[] cIds = {1,2,4 };
var result = from s in context.Students
             where cIds.All(id => s.StudentCourses.Any(sc=> sc.CID == id))
             select s;