public void UpdateProduct(Product product)
{
// help => http://www.entityframeworktutorial.net/EntityFramework4.3/update-many-to-many-entity-using-dbcontext.aspx
// don't forget equals implementation for objects
var existingProduct =
_context.Products.Include("Categories").FirstOrDefault(p => p.Id == product.Id);
if (existingProduct == null)
{
throw new ArgumentException("Product was not found");
}
var deleteCategories =
existingProduct.Categories.Except(product.Categories).ToList();
var addedCategories =
product.Categories.Except(existingProduct.Categories).ToList();
deleteCategories.ForEach(category => existingProduct.Categories.Remove(category));
foreach (Category category in addedCategories)
{
_context.Categories.Attach(category);
existingProduct.Categories.Add(category);
}
_context.SaveChanges();
_context.DetachAllEntities();
product.Categories.Clear();
_context.Products.Attach(product);
_context.Entry(product).State = EntityState.Modified;
_context.SaveChanges();
}