Update model with latest autoinc id from database

Question

Hello,

which method do you prefer to update my newly saved customer with the last autoincremented Id ?

Do you see any disadvantage in one of both methods?

CustomerRepository.cs

public int AddCustomer(Customer customer)
{
   //....
   return lastID;
}

BillingViewModel.cs

//Method 1
SelectedCustomer.Id = _customerRepo.AddCustomer(SelectedCustomer);

OR

   BillingViewModel.cs
    //Method 2

    _customerRepo.AddCustomer(ref SelectedCustomer);

    CustomerRepository.cs

    public void AddCustomer(ref Customer customer)
    {
       //...
       customer.Id = lastId;

    }