将项目分为项目和子项目

Question

I am using EF and and my query is returning a collection of the following as anonymous object

new
{
    CourseId,
    CourseCode,
    StudentId,
    StudentNo,
    StudentName,
    StudentSurname
}

and I have two following classes

public class Student
{
    public int StudentId { get; set; }
    public string StudentNo { get; set; }
    public string StudentName { get; set; }
    public string StudentSurname { get; set; }
}

public class Course
{
    public int CourseId { get; set; }
    public string CourseCode { get; set; }

    public List<Student> EnrolledStudents { get; set; }
}

The resulset might have several courses with students enrolled in each

How can I convert the result set into an list of objects as shown.

Regards.

Answer 1

I have found the solution. The following query does the trick:

List<Course> courses = (from item in resultset
                       group new
                       {
                           item.CourseId,
                           item.CourseCode,
                           item.StudentId,
                           item.StudentNo,
                           item.StudentName,
                           item.StudentSurname
                       }
                       by new
                       {
                           CourseId = item.CourseId,
                           CourseCode = item.CourseCode
                       } into _item
                       select new Course
                       {
                           CourseId = _item.Key.CourseId,
                           CourseCode = _item.Key.CourseCode
                           EnrolledStudents  = (from st in resultset.Where(x => x.CourseId == _item.Key.CourseId)
                                               select new Student
                                               {
                                                   StudentId = st.StudentId,
                                                   StudentNo = st.StudentNo,
                                                   StudentName =  st.StudentName,
                                                   StudentSurname = st.StudentSurname
                                               }).ToList()
                       }).ToList();

Answer 2

I would wonder why the EF query is bringing back denormalized data like that and if you cannot tackle the problem there, but sometimes you have to work with what you've got.

This should do the trick:

// assume the anon objects are in collection called 'items'
// in memory and data is all valid

// Get just one copy of each student
var students = items
    .Select(i => new { i.StudentId, i.StudentNo, i.StudentName, i.StudentSurname })
    .Distinct()
    .Select(i => new Student { 
        StudentId = i.StudentId, 
        StudentNo = i.StudentNo, 
        StudentName = i.StudentName, 
        StudentSurname = i.StudentSurname
    }); 

// Create courses and match up the students
var courses = items.GroupBy(i => i.CourseId).Select(gc => new Course            
    {   
        CourseId = gc.First().CourseId,
        CourseCode = gc.First().CourseCode,
        EnrolledStudents = gc.Join(students, i => i.StudentId, s => s.StudentId, (i, s) => s).ToList(),                                                                                 
    });

Answer 3

The following does work perfectly for me

var courses = resultset.GroupBy(
    row => new { row.CourseId, row.CourseCode },
    row => new Student
            {
                StudentId = row.StudentId,
                StudentName = row.StudentName,
                StudentNo = row.StudentNo,
                StudentSurname = row.StudentSurname,
            },
    (key, valueList) => new Course
                {
                    CourseId = key.CourseId,
                    CourseCode = key.CourseCode,
                    EnrolledStudents = valueList.ToList()
                }
).ToList();