How to save changes of courses in EmployeeCourse table - asp.net-mvc

Question

What i Need
I need to save changes in courses in EmployeeCourse table
by remove all course for employee from EmployeeCourse table
then add courses after changes
Problem
when add changes in courses after remove i get error in save changes() function
{"An error occurred while updating the entries.
The INSERT statement conflicted with the FOREIGN KEY constraint
\"FK_EmployeeCourse_Course\". The conflict occurred in database \"mycourse\",
table \"dbo.Course\", column 'Id'.\r\nThe statement has been terminated."}
under submit button edit [httppost]
public ActionResult Edit(EditEmployeeVm model)
{
var emp = db.Employees.FirstOrDefault(f => f.Id == model.Id);
// remove all courses
foreach (EmployeeCourse eec in emp.EmployeeCourses.ToList())
{
var ec = db.EmployeeCourses.Find(eec.Id);
db.EmployeeCourses.Remove(ec);
}
// add courses again
foreach (var couseid in model.CourseIds)
{
db.EmployeeCourses.Add(new EmployeeCourse { CourseId = couseid, EmployeeId = emp.Id });
}
db.SaveChanges();
}
Debug result
debug add as image below
Details
Relation between two tables one to many
EmployeeCourse
Id(primary key) CourseId(forign key) EmployeeId(forign key)
Course table in database
Id(pk) CourseName
I using following view model for edit to get CourseIds
#model StudentCourses.Models.EditEmployeeVm
$(function () {
$(document).on("click", ".remove", function (e) {
e.preventDefault();
$(this).closest(".course-item").remove();
});
$('#AvailableCourses').change(function () {
var val = $(this).val();
var text = $("#AvailableCourses option:selected").text();
var existingCourses = $("input[name='CourseIds']")
.map(function () { return this.value; }).get();
if (existingCourses.indexOf(val) === -1) {
var newItem = $("<div/>").addClass("course-item")
.append(text + ' Remove ');
newItem.append('<input type="text" name="CourseIds" value="' + val + '" />');
$("#items").append(newItem);
}
});
});
</script>
to retrieve courses from database in edit view i used code below
<div>
#using (Html.BeginForm())
{
#Html.HiddenFor(g => g.Id)
#Html.LabelFor(f => f.Name)
#Html.DropDownList("AvailableCourses", Model.Courses, "Select")
<h4>Existing courses</h4>
<div id="items"></div>
foreach (var c in Model.ExistingCourses)
{
<div class="course-item">
#c.Name Remove
<input type="text" name="CourseIds" value="#c.Id" />
</div>
}
}
</div>
model used for that as following
public class EditEmployeeVm
{
public int Id { set; get; }
public List<SelectListItem> Courses { get; set; }
public int[] CourseIds { set; get; }
public List<CourseVm> ExistingCourses { set; get; }
}
public class CourseVm
{
public int Id { set; get; }
public string Name { set; get; }
}
}
update
public ActionResult Edit(int id)
{
var vm = new EditEmployeeVm { Id = id };
var emp = db.Employees.FirstOrDefault(f => f.Id == id);
vm.Name = emp.Name;
vm.ExistingCourses = db.EmployeeCourses
.Where(g => g.EmployeeId == id)
.Select(f => new CourseVm
{
Id = f.Id,
Name = f.Course.CourseName
}).ToList();
vm.CourseIds = vm.ExistingCourses.Select(g => g.Id).ToArray();
vm.Courses = db.Courses.Select(f => new SelectListItem
{
Value = f.Id.ToString(),
Text = f.CourseName
}).ToList();
return View(vm);
}

Answer 1

In your EDIT Get action, You are using the wrong id for CourseVm. It should be the Course Id, but you are setting the EmployeeCourse record/entity Id.
This should fix it.
vm.ExistingCourses = db.EmployeeCourses.Where(g => g.EmployeeId == id)
.Select(f => new CourseVm
{
Id = f.Course.Id,
Name = f.Course.CourseName
}).ToList();