如何在C# linq中编写一对多关系查询

using System;
using System.Collections.Generic;
using System.Linq;

public class Order
{
    public int OrderId { get; set; }
    public string CustomerName { get; set; }
}

public class OrderItem
{
    public int OrderId { get; set; }
    public string ProductName { get; set; }
}

public class Program
{
    public static void Main(string[] args)
    {
        List<Order> orders = new List<Order>
        {
            new Order { OrderId = 1, CustomerName = "John" },
            new Order { OrderId = 2, CustomerName = "Jane" }
        };

        List<OrderItem> orderItems = new List<OrderItem>
        {
            new OrderItem { OrderId = 1, ProductName = "Product 1" },
            new OrderItem { OrderId = 1, ProductName = "Product 2" },
            new OrderItem { OrderId = 2, ProductName = "Product 3" }
        };

        var query = from order in orders
                    join orderItem in orderItems on order.OrderId equals orderItem.OrderId into orderGroup
                    select new
                    {
                        OrderId = order.OrderId,
                        CustomerName = order.CustomerName,
                        OrderItems = orderGroup.Select(oi => oi.ProductName).ToList()
                    };

        foreach (var result in query)
        {
            Console.WriteLine($"Order ID: {result.OrderId}");
            Console.WriteLine($"Customer Name: {result.CustomerName}");
            Console.WriteLine("Order Items:");
            foreach (var item in result.OrderItems)
            {
                Console.WriteLine(item);
            }
            Console.WriteLine();
        }
    }
}