实体框架递归地填充DTO的子项

public class OrderDTO
{
    public int OrderId { get; set; }
    public string CustomerName { get; set; }
    public List<OrderItemDTO> OrderItems { get; set; }
}

public class OrderItemDTO
{
    public int OrderItemId { get; set; }
    public string ProductName { get; set; }
    public decimal Price { get; set; }
}

public OrderDTO GetOrder(int orderId)
{
    using (var context = new MyDbContext())
    {
        var orderEntity = context.Orders
            .Include(o => o.OrderItems) // 加载订单项子项
            .FirstOrDefault(o => o.OrderId == orderId);

        if (orderEntity == null)
            return null;

        var orderDTO = new OrderDTO
        {
            OrderId = orderEntity.OrderId,
            CustomerName = orderEntity.CustomerName,
            OrderItems = new List<OrderItemDTO>()
        };

        foreach (var orderItemEntity in orderEntity.OrderItems)
        {
            var orderItemDTO = new OrderItemDTO
            {
                OrderItemId = orderItemEntity.OrderItemId,
                ProductName = orderItemEntity.ProductName,
                Price = orderItemEntity.Price
            };

            orderDTO.OrderItems.Add(orderItemDTO);
        }

        return orderDTO;
    }
}