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);
}

Mark Tabor · Answer

still it save null for student and course id

Mark Tabor · Answer

Ashutosh Gupta
as my student_Id and course_ID properties of type int array in model class

Ashutosh Gupta · Answer

int  i = o     foreach(var student in SAC.Student_id)     {     int  j = 0;     foreach(var course in SAC.Course_Id)     {     Student_Assigned_courses Sa =  new  Student_Assigned_courses();     Sa.Student_id = Convert.ToInt32(student [i].ToString());     Sa.Course_Id = Convert.ToInt32(course[j].toString());     Sa.Module_Id = SAC.Module_Id;     Sa.Year_Id = SAC.Year_Id;     Sa.Program_Id = SAC.Program_Id;     db.StudentCoursesAssigned.Add(Sa);     j++;     }     i++;     }     did you try with my code, it seems your code has extra loop , check values during debugging time, if values does not match with data type, then DB save operation can fail.

Mark Tabor · Answer

Ashutosh Gupta I get struck in saving the record to the db below is my controller code  [HttpPost] // [ValidateAntiForgeryToken] public ActionResult Create(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]; // SAC.Student_id[i] = s; Sa.Student_id[i] = s; string[] selitems = frmcollection.GetValues("Student_id"); 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); // Sa.Student_id = SAC.Student_id[i]; } if (db.SaveChanges() > 0) { TempData["MessageDesignation"] = "Department Saved Successfully!"; } } } return RedirectToAction("Index"); } return View(SAC); } in inspect the values and they are there while debugging

Ashutosh Gupta · Answer

right, hence do not keep array in DB because anyways you are creating 6 entries in database.   when you load from DB to display in view, just group that data using Linq and send to view.

Mark Tabor · Answer

Ashutosh Gupta you are right , but i have multi select dropdown list on view and i want to give an option to the user to select multiple courses and multiple students at the same time , I mean if i select two students and 3 courses then in db it will save 6 rows , 3 courses for student A and 3 courses for student B

Ashutosh Gupta · Answer

mark, why do you want to have array of studentid and course id ? anyways you will be saving each student and course as new row. e.g. 2 student with 3 courses will have 6 new rows in database.    just make it simple schema. [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; }   }     int  i = o   foreach(var student in SAC.Student_id)   {   int  j = 0;   foreach(var course in SAC.Course_Id)   {   Student_Assigned_courses Sa =  new  Student_Assigned_courses();   Sa.Student_id = Convert.ToInt32(student [i].ToString());   Sa.Course_Id = Convert.ToInt32(course[j].toString());   Sa.Module_Id = SAC.Module_Id;   Sa.Year_Id = SAC.Year_Id;   Sa.Program_Id = SAC.Program_Id;   db.StudentCoursesAssigned.Add(Sa);   j++;   }   i++;   }

Mark Tabor · Answer

Ashutosh Gupta after adding constructor it have the values now , but on saving it is not saving into the database the student id and course id are saved as null can you check the attachment in which i explain everything with screensthot

Mark Tabor · Answer

Sa.Student_id[i]=s; this gives error of object reference is not set to an instance of object

Ashutosh Gupta · Answer

Mark,    i see the actual problem now..   you need to initialize your   int[] Student_id and int[] Course_Id.    create constructor of  your class with size of these array.  e.g.   public  Student_Assigned_courses( int  courselen,  int  srudentlen)           {               Course_Id =  new   int [courselen];               Student_id =  new   int [srudentlen];           }    and when you call this  Student_Assigned_courses Sa = new Student_Assigned_courses(SAC.Course_Id.Lenght, SAC.Student_id.Length);  it will work now..