public async Task <Customer> AddCustomerAsync(Customer customer)
        {
            using (DBProjContext db = new DBProjContext())
            {
                db.Customers.Add(customer);
                await db.SaveChangesAsync();

                return(customer);
            }
        }
        public async Task DeleteCustomerAsync(long customerId)
        {
            using (DBProjContext db = new DBProjContext())
            {
                var customer = db.Customers.FirstOrDefault(x => x.Id == customerId);

                if (customer != null)
                {
                    db.Customers.Remove(customer);
                }

                await db.SaveChangesAsync();
            }
        }
        public async Task <Customer> UpdateCustomerAsync(Customer customer)
        {
            using (DBProjContext db = new DBProjContext())
            {
                if (!db.Customers.Local.Any(x => x.Id == customer.Id))
                {
                    db.Customers.Attach(customer);
                }

                db.Entry(customer).State = EntityState.Modified;
                await db.SaveChangesAsync();

                return(customer);
            }
        }