c# - 查询 c# 列表以限制子项但返回父项

Question

我有一个嵌套列表结构，其中包含 Customers -> Orders -> OrderItems。我试图找到一个 LINQ 或其他查询，它将返回客户及其嵌套项目，其中 OrderItem 数量 = 1。但是，它不应返回任何订单或数量 != 1 的 OrderItems。

我试过这个:

var customers2 = customers.Where(c => c.Orders.Any(o => o.OrderItems.Exists(oi => oi.Quantity == 1)));

它仅正确返回订单商品数量 = 1 的客户，但它也返回所有其他订单和订单商品。

我可以用几个 For-each 循环得到想要的结果，但我想找到更优雅的东西:

        foreach (var customer in customers2)
        {
            customer.Orders = customer.Orders.Where(o => o.OrderItems.Exists(oi => oi.Quantity == 1)).ToList();

            foreach (var order in customer.Orders)
            {
                order.OrderItems = order.OrderItems.Where(oi => oi.Quantity == 1).ToList();
            }
        }

这是对象结构和一些示例数据。

public class Customer
{
    public int CustomerId { get; set; }
    public string Name { get; set; }
    public string Address { get; set; }
    public List<Order> Orders { get; set; }
}

public class Order
{
    public int OrderId { get; set; }
    public int CustomerId { get; set; }
    public DateTime OrderDate { get; set; }
    public bool Shipped { get; set; }
    public List<OrderItem> OrderItems { get; set; }
}

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

        var customers = new List<Customer>
        {
            new Customer
            {
                CustomerId = 1,
                Name = "Shawn",
                Address = "123 Main Street",
                Orders = new List<Order>()
                {
                    new Order()
                    {
                        OrderId = 100,
                        CustomerId = 1,
                        OrderDate = DateTime.Now,
                        Shipped = true,
                        OrderItems = new List<OrderItem>()
                        {
                            new OrderItem()
                            {
                                OrderItemId = 200,
                                OrderId = 100,
                                ItemName = "Computer",
                                Quantity = 1
                            },
                            new OrderItem()
                            {
                                OrderItemId = 206,
                                OrderId = 100,
                                ItemName = "Hard Drive",
                                Quantity = 2
                            }
                        }
                    },
                    new Order()
                    {
                        OrderId = 106,
                        CustomerId = 1,
                        OrderDate = DateTime.Now,
                        Shipped = true,
                        OrderItems = new List<OrderItem>()
                        {
                            new OrderItem()
                            {
                                OrderItemId = 207,
                                OrderId = 106,
                                ItemName = "Monitor",
                                Quantity = 3
                            },
                            new OrderItem()
                            {
                                OrderItemId = 208,
                                OrderId = 106,
                                ItemName = "DVD Burner",
                                Quantity = 2
                            }
                        }
                    }
                }
            },
            new Customer
            {
                CustomerId = 2,
                Name = "Arianna",
                Address = "456 Main Street",
                Orders = new List<Order>()
                {
                    new Order()
                    {
                        OrderId = 101,
                        CustomerId = 2,
                        OrderDate = DateTime.Now.AddDays(-10),
                        Shipped = true,
                        OrderItems = new List<OrderItem>()
                        {
                            new OrderItem()
                            {
                                OrderItemId = 201,
                                OrderId = 101,
                                ItemName = "barbie",
                                Quantity = 2
                            }
                        }
                    }
                }
            },
            new Customer
            {
                CustomerId = 3,
                Name = "Ryan",
                Address = "789 Main Street",
                Orders = new List<Order>()
                {
                    new Order()
                    {
                        OrderId = 102,
                        CustomerId = 3,
                        OrderDate = DateTime.Now.AddDays(-5),
                        Shipped = true,
                        OrderItems = new List<OrderItem>()
                        {
                            new OrderItem()
                            {
                                OrderItemId = 203,
                                OrderId = 103,
                                ItemName = "Minecraft",
                                Quantity = 2
                            }
                        }
                    }
                }
            }
        };

Answer 1

你走在正确的道路上

var customers2 = customers
    .Where(c => c.Orders.Any(o => o.OrderItems.Exists(oi => oi.Quantity == 1)));

您只需要一个额外的步骤，因为您不能同时过滤订单和客户，您已经过滤了客户以仅获取您感兴趣的客户，现在自己过滤订单

var customers2 = customers
    .Where(c => c.Orders.Any(o => o.OrderItems.Exists(oi => oi.Quantity == 1)))
    .Select(c => c.Orders.Where(o => o.OrderItems(o => o.OrderItems.Exists(oi => oi.Quantity == 1)));

然而，这给您留下了 ienumerable 的 ienumerable 的订单，而不是客户，但是您不能完全按照您的意愿进行操作(检索客户并更改他们的订单属性)，因为这会更改他们的原始订单列表，您可以做的是创建一个匿名类型，以在您的查询中存储订单和客户，这样选择:

var customers2 = customers
    .Where(c => c.Orders.Any(o => o.OrderItems.Exists(oi => oi.Quantity == 1)))
    .Select(c => new
       {
       Customer = c,
       FilteredOrders =  c.Orders.Where(o => o.OrderItems(o => o.OrderItems.Exists(oi => oi.Quantity == 1))
       });

现在你可以这样使用了

foreach(var cust in customers2)
{
   cust.Customer // your original Customer object
   cust.Customer.Orders // your original orders collection for this Customer
   cust.FilteredOrders // only the orders you're interested in for this customer
}