C# - Lambda -对包含嵌套列表对象的列表数据进行分组

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

public class OrderItem
{
    public int ProductId { get; set; }
    public string ProductName { get; set; }
    public decimal Price { get; set; }
}

public class Order
{
    public int OrderId { get; set; }
    public List<OrderItem> Items { get; set; }
}

public class Program
{
    public static void Main()
    {
        List<Order> orders = new List<Order>
        {
            new Order
            {
                OrderId = 1,
                Items = new List<OrderItem>
                {
                    new OrderItem { ProductId = 1, ProductName = "Product A", Price = 100 },
                    new OrderItem { ProductId = 2, ProductName = "Product B", Price = 200 }
                }
            },
            new Order
            {
                OrderId = 2,
                Items = new List<OrderItem>
                {
                    new OrderItem { ProductId = 1, ProductName = "Product A", Price = 100 },
                    new OrderItem { ProductId = 3, ProductName = "Product C", Price = 300 }
                }
            }
        };

        var groupedItems = orders.SelectMany(o => o.Items)
                                 .GroupBy(item => item.ProductId)
                                 .Select(group => new
                                 {
                                     ProductId = group.Key,
                                     TotalPrice = group.Sum(item => item.Price),
                                     Count = group.Count()
                                 });

        foreach (var group in groupedItems)
        {
            Console.WriteLine($"Product ID: {group.ProductId}, Total Price: {group.TotalPrice}, Count: {group.Count}");
        }
    }
}

var sortedGroupedItems = groupedItems.OrderBy(g => g.ProductId);