如何从嵌套的select查询linq读取数据

// 假设有两个实体类：Order（订单）和 OrderItem（订单项）
public class Order
{
    public int OrderId { get; set; }
    public string CustomerName { get; set; }
}

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

// 假设有两个数据集：orders（订单集合）和 orderItems（订单项集合）
List<Order> orders = new List<Order>
{
    new Order { OrderId = 1, CustomerName = "Customer 1" },
    new Order { OrderId = 2, CustomerName = "Customer 2" }
};

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

// 使用LINQ进行嵌套查询
var query = from order in orders
            select new
            {
                order.OrderId,
                order.CustomerName,
                OrderItems = from item in orderItems
                             where item.OrderId == order.OrderId
                             select item
            };

// 遍历查询结果并输出
foreach (var result in query)
{
    Console.WriteLine($"Order ID: {result.OrderId}, Customer Name: {result.CustomerName}");
    foreach (var item in result.OrderItems)
    {
        Console.WriteLine($"Order Item ID: {item.OrderItemId}, Product Name: {item.ProductName}");
    }
}