Saving Multiple Selected dropdownlist values into Db

Question

Hi I just want to ask someone who can assists me completely , below is the detail of the problem i am getting struck with. 

I have web application in asp.net mvc4, in which i have students, courses and i am going to assign courses to students below are the table structure , i am omitting the rest of the columns and just showing the base columns for understanding purposes.

 

Student TAble: 

Student_Id	Name
1	ASAD
2	TALHA

Course Table:

Course_Id	Name
1	MATH
2	PHYSICS

StudentVsCourses TAble:

Table_id	student_Id	Course_ID
1	1	2
2	1	1
3	2	1
4	2	2

 

 

Below is my view in which  i have multi select dropdown list to select multiple course and multiple students.Like if i select two students and 4 courses then it need to insert 8 rows into the database like assign four courses to student A and four courses to student B

 I omit the other columns like program,Year,Module as i would apply the same logic for them if i get success with courses and student.
below is my model class in which i am taking student & courses properties as array , and when i post these values my controller is getting the selected values as arrays , but i am confuse about how to save them i need complete code of saving the courses for each students like loop through students first and then assign all selected courses , then get back to student loop and do the same assigned for the next selected student .

 

Model class:

[Table("Student_courses")]

public class Student_Assigned_courses

{

[Key]

[Display(Name = " ID")]

public int Id { get; set; }

[Display(Name = "student Name ")]

public int[] Student_id { get; set; }

[Display(Name = "Course ")]

[Required(ErrorMessage = "course is Required")]

public int[] Course_Id { get; set; }

[Display(Name = "Module Name")]

[Display(Name = "Program Name")]

[Required(ErrorMessage = "Program selection is required field!")]

public int Program_Id { get; set; }

[Display(Name = "Year")]

[Required(ErrorMessage = "Year selection is required field!")]

public int Year_Id { get; set; }

}

}
Controller Code :

[HttpPost]

// [ValidateAntiForgeryToken]

public ActionResult Create([Bind(Include = "Id,Year_Id,Program_Id,Student_id,Module_Id,Course_Id")]Student_Assigned_courses SAC,FormCollection frmcollection)

{

ViewBag.PopulatePrograms = _IEducation.PopulatePrograms();

if (SAC.Student_id != null)

{

foreach(var student in SAC.Student_id)

{

foreach(var course in SAC.Course_Id)

{

Student_Assigned_courses Sa = new Student_Assigned_courses();

for(int i=0;i

{

int s = SAC.Student_id[i];

string[] selitems = frmcollection.GetValues("Student_id");

Sa.Student_id[i] = Convert.ToInt32(SAC.Student_id[i].ToString());// this line gives error as object reference is not set to an instance of object although the  i is initialized in the loop above .

Sa.Course_Id = SAC.Course_Id;

Sa.Module_Id = SAC.Module_Id;

Sa.Year_Id = SAC.Year_Id;

Sa.Program_Id = SAC.Program_Id;

db.StudentCoursesAssigned.Add(Sa);

}

if (db.SaveChanges() > 0)

{

TempData["MessageDesignation"] = "Department Saved Successfully!";

}

}

}

return RedirectToAction("Index");

}

return View(SAC);

}