c# - Entity Framework: Removing child entity

Question

I am trying to remove category object from News but it doesn't work

My code looks like this:

var OriginalCategoriesIds = db.News.Where(w => w.NewsId == 1)
                                   .SelectMany(v => v.Categories)
                                   .ToList();
News NewsToUpdate = new News() { NewsId = 1 };
db.News.Attach(NewsToUpdate);

foreach (var category in OriginalCategoriesIds)
{
    if (!model.SelectedCategoriesIds.Contains(category.CategoryId))
    {
        NewsToUpdate.Categories.Remove(category);
    }
}

db.SaveChanges();

Answer 1

Here is your issue:

var OriginalCategoriesIds = db.News.Where(w => w.NewsId == 1).SelectMany(v => v.Categories).ToList();
                            News NewsToUpdate = new News() { NewsId = 1 };
                            db.News.Attach(NewsToUpdate);

                            foreach (var category in OriginalCategoriesIds)
                            {
                                if (!model.SelectedCategoriesIds.Contains(category.CategoryId))
                                {
                                    db.News.Categories.Remove(category);// <---change like this
                                }

                            }

                            db.SaveChanges();