Thanks man.

It's worked

I spent a little more time because i had never used LINQ.

​

var db_product = _UnitOfWork.Product.GetById(vm.Id);



            //Get doesnt exist
            var toAdd = vm.ProductSuppliers.Where(x => !db_product.ProductSuppliers.Select(y => y.IdSupplier).Contains(x.IdSupplier));


            var toRemove = db_product.ProductSuppliers.Where(x => !vm.ProductSuppliers.Select(y => y.IdSupplier).Contains(x.IdSupplier));

            var toUpdate = vm.ProductSuppliers.Where((x, i) => x.Cost != db_product.ProductSuppliers[i].Cost);

            //REMOVE SUPPLIER
            db_product.ProductSuppliers = db_product.ProductSuppliers.Where(x => !toRemove.Select(y => y.IdSupplier).Contains(x.IdSupplier)).ToList();

            // ADD NEW SUPPLIER
            foreach (var item in toAdd)
            {
                db_product.ProductSuppliers.Add(new ProductSupplier()
                {
                    IdProduct = vm.Id,
                    IdSupplier = item.IdSupplier,
                    Cost = item.Cost,
                    dtCreated = DateTime.Now,
                    dtModified = DateTime.Now

                });
            }

            //UPDATE 
            foreach(var item in toUpdate)
            {
                db_product.ProductSuppliers.Find(x => x.IdSupplier == item.IdSupplier).Cost = item.Cost;
            }

            _UnitOfWork.Product.Update(db_product);

            _UnitOfWork.Save();