How to insert in a join table, for many-to-many relationship?

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MVC

C#5.0

entity-framework

I have two entities that have a many-to-many relationship

First Class:

public class StatutFicheSinistre
    {
        public int StatutFicheSinistreID { get; set; }
        public string codeStatutFS { get; set; }
        public DateTime DateSurvenance { get; set; }
        [Display(Name = "Date de Declaration")]
        public DateTime DateDeclaration { get; set; }
               public int VehiculeID { get; set; }
        public int FicheSinistreID { get; set; }


        public virtual Vehicule Vehicule { get; set; }
        public virtual FicheSinistre FicheSinistre { get; set; }
        public virtual ICollection<Evenement> Evenements { get; set; }
        public virtual ICollection<DocDeclaration> DocDeclarations { get; set; }
        
    }

second class

 public class Evenement
{
    public int EvenementID { get; set; }
    public string CodeEvenement { get; set; }

    public virtual ICollection<StatutFicheSinistre> StatutFicheSinistres { get; set; }
}

I have created the following ViewModel StatutFSEvenement

public class StatutFSEvenement
    {
        public int EvenementID { get; set; }
        public string CodeEvenement { get; set; }
        public bool designee { get; set; }
    }

In the First Class controller,in the edit, index and create actions, I have retrieved the events that are related to a certain statutFicheSinistre. If I manually insert data in the database it's shown correctly, however, if I try to update or create a new StatutFicheSinistre and Associate evnts with it it doesn't work.

I think I should specify in the EvenementController but I don't know how.


this is the POST Edit Action in the Controller

 [HttpPost, ActionName("Edit")]
 [ValidateAntiForgeryToken]
 public ActionResult EditPost(int? id, string[] selectedEvents)
{
 var statutFicheSinistreToUpdate = db.StatutFichesSinistres
    .Include(i => i.FicheSinistre)
    .Include(i=>i.Evenements)
    .Where(i => i.StatutFicheSinistreID == id)
    .Single();
    if (TryUpdateModel(statutFicheSinistreToUpdate, "",
   new string[] { "codeStatutFS", "DateSurvenance", "DateDeclaration",
     "Vehicule","FicheSinistre"}))
     {
         try
         {
                          if(String.IsNullOrWhiteSpace(statutFicheSinistreToUpdate.Vehicule.Immatriculation))
             {
                 statutFicheSinistreToUpdate.Vehicule = null;
             }
             UpdateSinistreEvenement(selectedEvents, statutFicheSinistreToUpdate);


             db.Entry(statutFicheSinistreToUpdate).State = EntityState.Modified;
             db.SaveChanges();
             return RedirectToAction("Index");
         }catch(RetryLimitExceededException /*dex*/)
         {
            ModelState.AddModelError("","Unable to save changes try again, and     if the problem persists see your system administrator");
         }
     }
     // method to provide information for the check box array using the StatutFSEvenement view model class
     PopulateAssignedEventData(statutFicheSinistreToUpdate);
     return View(statutFicheSinistreToUpdate);
 }

Whilst creating or updating a StatutFicheSinitre If I check any of the checkboxes that contain the Events nothing happens.