I am learning some concepts in asp.net mvc. I use the entity structure and visual studio of 2013. I am creating a demo application for training. I created a model according to this link. Models are as follows. Below is a model of the course. The course has a department as a foreign key. A department can have many courses.
using System; using System.Collections.Generic; using System.Linq; using System.Web; namespace ManyItemsDemo2.Models { public class Course { public int CourseID { get; set; } public string Title { get; set; } public string Credits { get; set; } public int DepartmentID { get; set; } public virtual Department Department { get; set; } } }
This is a department model. The department model is simple. This is due to the course model.
using System; using System.Collections.Generic; using System.Linq; using System.Web; namespace ManyItemsDemo2.Models { public class Department { public Department() { this.Cources = new HashSet<Course>(); } public int DepartmentID { get; set; } public string Name { get; set; } public double Budget { get; set; } public string Administrator { get; set; } public virtual ICollection<Course> Cources { get; set; } } }
There is a context class.
using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Data.Entity; namespace ManyItemsDemo2.Models { public class SchoolContext:DbContext { public SchoolContext() : base("SchoolContext") { } public DbSet<Course> Courses { get; set; } public DbSet<Department> Departments { get; set; } } }
Now I used scafolding and created controllers and views with CRUD functionality. I can create a department and viewing courses. Now I need to assign several courses when creating departments. Therefore, I created this presentation model. Here, one department has many courses.
using System; using System.Collections.Generic; using System.Linq; using System.Web; using ManyItemsDemo2.Models; namespace ManyItemsDemo2.ViewModels { public class DeptCourses { public Department Department { get; set; } public IEnumerable<Course> Course { get; set; } } }
along with this I created a new view. Which can take more courses when creating a department. The result is as follows. 
The plus button has a script, which is from my previous question here . The script uses jquery and clones the dropdown menu and adds it back.
The problem starts here. When I add more than one drop-down list, say 3, I get null in the controller, although I get three elements, only one element matters, the others null. See Image for more explanation.
Why is this happening? PS: I could ignore real-time scenarios, as this is a demo application for learning and eliminating concepts from one to many relationships with entity infrastructure along with using MVC.