Question

I have an SQL query (below) that essentially takes a student from tbStudents, and then gets the most recent term (a number, but stored as a string) in tbTerms.

There is a one-to-many relationship with a student in tbStudents to a term record in tbTerms. Example:

tbStudents:

StudentId FirstName LastName
12345     John      Smith
12346     Jane      Doe

tbTerms:

StudentId Term
12345     1234
12345     1235
12345     1236
12346     1233
12346     1234

Desired:

StudentId FirstName LastName Term
12345     John      Smith    1236
12346     Jane      Doe      1234

SQL Query:

select tbStudents.student_id, tbStudents.user_id, tbStudents.firstname, tbStudents.lastname, v.rTerm
    from  tbStudents
    inner join (
        select tbTerms.student_id, MAX(tbTerms.term) as rTerm
        from tbTerms
        group by tbTerms.student_id
    ) v on v.student_id = tbStudents.student_id

I’ve been trying to get this all into one LINQ statement, but I’m having trouble. Is there anyway to do this in one statement? Or must it be done in multiple statements. Thanks in advanced.

Edit: C# code of what I have tried.

var students = (from s in dockDb.tbStudents
                join t in dockDb.tbTerms on s.student_id equals t.student_id
                into pairs
                from p in pairs
                select new { UserId = s.user_id, StudentId = s.student_id, Term = p.term } ).ToList();

Output is similar to:

StudentId FirstName LastName Term
12345     John      Smith    1234
12345     John      Smith    1235
12345     John      Smith    1236
12346     Jane      Doe      1233
12346     Jane      Doe      1234

Edit #2: I’m using Entity Framework for data. I’m not sure if this affects anything, but most of the solutions are ‘Syntactically incorrect’ when I attempt them.

Answer 1

Should be possible. Try this:

from s in Students
join t in Terms on t.StudentId = s.StudentId
select new {Student = s, Term = t}
group by s into g
select new {g.Key.StudentId, g.Key.FirstName, g.Key.LastName, g.Max(x=>x.Term.term)};

Breaking it down, the first two lines define the domain in which to search; namely, the inner-joined combination of Students and Terms, linked by StudentId. Each unique combination of Student and Term are put into an anonymous type, and then those instances are grouped by each unique Student into a Lookup (a read-only collection of IEnumerables referenced by key). The, we can select the key’s (Student’s) vital info, and in the list of terms, find the one with the highest value (which will be the most recent).