Updating Collections properly using EF Core

ChangingCollections.cs

class Controller {
  public IActionResult Put(Model posted) {
    foreach (var item in fromDb.Collection)
      {
        var editedItem = posted.Collection.FirstOrDefault(a => item.Id == a.Id);
        if(editedItem is null)
          Db.Remove(item);
        else
          Db.Entry(item).CurrentValues.SetValues(editedItem);
      }
      foreach (var item in post.Collection.Where(a => fromDb.Collection.All(b => b.Id != a.Id)))
      {
        fromDb.Collection.Add(item);
        Db.Add(item);
      }
  }
}
// Generic version to be used as extension method
public static void UpdateCollection<T>(this Controller controller, DbContext db, ICollection<T> fromDb, ICollection<T> posted, Func<T, T, bool> idSelector) where T : class
  {
    foreach (var item in fromDb)
    {
      var editedItem = posted.FirstOrDefault(a => idSelector(a, item));
      if (editedItem is null)
        db.Remove(item);
      else
        db.Entry(item).CurrentValues.SetValues(editedItem);
    }
    foreach (var item in posted.Where(a => fromDb.All(b => !idSelector(a, b))))
    {
      fromDb.Add(item);
      db.Add(item);
    }
  }
//