LINQ查询:带有另一个表的Count元素的新查询对象

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

public class Order
{
    public int OrderId { get; set; }
    public int CustomerId { get; set; }
}

public class Customer
{
    public int CustomerId { get; set; }
    public string Name { get; set; }
}

public class Program
{
    public static void Main()
    {
        var orders = new List<Order>
        {
            new Order { OrderId = 1, CustomerId = 1 },
            new Order { OrderId = 2, CustomerId = 2 },
            new Order { OrderId = 3, CustomerId = 1 },
            new Order { OrderId = 4, CustomerId = 3 }
        };

        var customers = new List<Customer>
        {
            new Customer { CustomerId = 1, Name = "Alice" },
            new Customer { CustomerId = 2, Name = "Bob" },
            new Customer { CustomerId = 3, Name = "Charlie" }
        };

        var customerOrderCounts = from c in customers
                                  select new
                                  {
                                      Customer = c,
                                      OrderCount = orders.Count(o => o.CustomerId == c.CustomerId)
                                  };

        foreach (var item in customerOrderCounts)
        {
            Console.WriteLine($"{item.Customer.Name}: {item.OrderCount} orders");
        }
    }
}