How to avoid parent entities beeing reinserted in EF6 - dealing with many to many relationship? - entity-framework

Question

Im new to EF6 and facing the following issue:
If I add my model via db.Modelclass.Add( model )-method and save the changes to the db new entities will be created in the tables Tours and ToursEmployees like it should for the model, but also in my parent table Employees. Last one is my use in the code below.
I already read this article about the issue https://msdn.microsoft.com/en-us/magazine/dn166926.aspx but in my case I dont know what to do, cause Im dealing with a many-to-many realtionship. I used code first and marked the artibutes in the models via virtual as navigation properties, so the framework created me a join table.
Whats the right way to use the framework for this kinda relaltionships, maybe creating a model for the joined table and then using the FK described in the article?
public ActionResult Create(TourViewModel tourVM) {
if (ModelState.IsValid) {
Tour tour = new Tour() {
Tourname = tourVM.Tourname,
Tourdate = tourVM.Tourdate,
VehicleId = tourVM.VehicleId
,Employees = new List<Employee>()
};
for (var i = 0; i < tourVM.Employees.Count; i++)
if (tourVM.Employees[i].Assigned)
tour.Employees.Add(
new Employee() { EmployeeId = tourVM.Employees[i].EmployeeId }
);
db.Tours.Add(tour);
db.SaveChanges();
return RedirectToAction("Index");
}
return View(tourVM);
}

Answer 1

I believe this is happening because you are adding the employees to the list that are not bound to the data context. Doing something like the below should work and correctly bind them to the data context object.
public ActionResult Create(TourViewModel tourVM) {
if (ModelState.IsValid) {
Tour tour = new Tour() {
Tourname = tourVM.Tourname,
Tourdate = tourVM.Tourdate,
VehicleId = tourVM.VehicleId,
Employees = new List<Employee>()
};
var IDs = tourVM.Employees.Where(e => e.Assigned).Select(e => e.EmployeeId);
var Employees = db.Employees.Where(e => IDs.Contains(e.EmployeeId)).ToList();
tour.Employees.AddRange(Employees);
db.Tours.Add(tour);
db.SaveChanges();
return RedirectToAction("Index");
}
return View(tourVM);
}