Order.cs

public class FulfillOrder
{
    private readonly DbContext _dbContext;

    public FulfillOrder(DbContext dbContext)
    {
        _dbContext = dbContext;
    }

    public async Task Handle(int orderId)
    {
        var order = await _dbContext.Orders.FindAsync(orderId);
        order.Status = OrderStatus.Fulfilled; 
        await _dbContext.SaveChangesAsync();
    }
}