C# LINQ select group

void Main()
{

	List<Order> orders = new List<Order>
		{
			new Order { OrderID = 1, OrderDate = DateTime.Parse("2023-09-21") },
			new Order { OrderID = 2, OrderDate = DateTime.Parse("2023-09-22") },
            // 添加更多订单
        };

	List<OrderDetail> orderDetails = new List<OrderDetail>
		{
			new OrderDetail { OrderDetailID = 1, OrderID = 1, ProductID = 101, UnitPrice = 10.0m, Quantity = 2 },
			new OrderDetail { OrderDetailID = 2, OrderID = 1, ProductID = 102, UnitPrice = 15.0m, Quantity = 3 },
			new OrderDetail { OrderDetailID = 3, OrderID = 2, ProductID = 103, UnitPrice = 20.0m, Quantity = 4 },
            // 添加更多订单详情
        };

	var query = from order in orders
				join orderDetail in orderDetails on order.OrderID equals orderDetail.OrderID into orderGroup
				select new
				{
					Order = order,
					OrderDetails = orderGroup.ToList()
				};

	foreach (var result in query)
	{
		Console.WriteLine($"Order ID: {result.Order.OrderID}, Order Date: {result.Order.OrderDate}");
		Console.WriteLine("Order Details:");
		foreach (var orderDetail in result.OrderDetails)
		{
			Console.WriteLine($" - ProductID: {orderDetail.ProductID}, Unit Price: {orderDetail.UnitPrice}, Quantity: {orderDetail.Quantity}");
		}
		Console.WriteLine();
	}
}

// Define other methods and classes here
public class Order
{
	public int OrderID { get; set; }
	public DateTime OrderDate { get; set; }
	// 其他订单相关的属性
}

public class OrderDetail
{
	public int OrderDetailID { get; set; }
	public int OrderID { get; set; }
	public int ProductID { get; set; }
	public decimal UnitPrice { get; set; }
	public int Quantity { get; set; }
	// 其他订单详情相关的属性
}

執行結果

Order ID: 1, Order Date: 2023/9/21 上午 12:00:00
Order Details:
 - ProductID: 101, Unit Price: 10.0, Quantity: 2
 - ProductID: 102, Unit Price: 15.0, Quantity: 3

Order ID: 2, Order Date: 2023/9/22 上午 12:00:00
Order Details:
 - ProductID: 103, Unit Price: 20.0, Quantity: 4