LINQ中扁平化的父母子女協會的數量

Question

我想算一些沒有孩子的父母和父母的孩子。 在我寫這篇文章時，我意識到用代碼更好地解釋了..所以，這里有：

使用以下示例類型：

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

public class Order
{
    public int Id { get; set; }
    public string Description { get; set; }
}

這個數據：

var customers = new List<Customer>
{
    new Customer
    {
        Id = 2,
        Name = "Jane Doe"
    },
    new Customer
    {
        Id = 1,
        Name = "John Doe",
        Orders = new List<Order>
        {
            new Order { Id = 342, Description = "Ordered a ball" },
            new Order { Id = 345, Description = "Ordered a bat" }
        }
    }
};

// I'm trying to get a count of customer orders added with customers with no orders
// In the above data, I would expect a count of 3 as detailed below
//
// CId      Name        OId
// ----     --------    ----
//  2       Jane Doe
//  1       John Doe    342
//  1       John Doe    345

int customerAndOrdersCount = {linq call here}; // equals 3

我試圖得到3回。

預先感謝您的幫助。

-Jessy Houle

之后添加：

所有偉大（和快速）的答案讓我印象深刻。 對於其他人來到這個問題，尋找一些選項，這里是一個單元測試，下面是一些工作示例。

[TestMethod]
public void TestSolutions()
{
    var customers = GetCustomers(); // data from above

    var count1 = customers.Select(customer => customer.Orders).Sum(orders => (orders != null) ? orders.Count() : 1);
    var count2 = (from c in customers from o in (c.Orders ?? Enumerable.Empty<Order>() ).DefaultIfEmpty() select c).Count();
    var count3 = customers.Sum(c => c.Orders == null ? 1 : c.Orders.Count());
    var count4 = customers.Sum(c => c.Orders==null ? 1 : Math.Max(1, c.Orders.Count()));


    Assert.AreEqual(3, count1);
    Assert.AreEqual(3, count2);
    Assert.AreEqual(3, count3);
    Assert.AreEqual(3, count4);
}

再次，謝謝大家的幫助！

Answer 1

怎么樣

int customerAndOrdersCount = customers.Sum(c => c.Orders==null ? 1 : Math.Max(1, c.Orders.Count()));

Answer 2

如果要使用空列表而不是null來初始化Order屬性，則可以執行以下操作：

int count =
  (
    from c in customers
    from o in c.Orders.DefaultIfEmpty()
    select c
  ).Count();

---

如果您決定保留未初始化的屬性，那么請執行以下操作：

int count =
  (
    from c in customers
    from o in (c.Orders ?? Enumerable.Empty<Order>() ).DefaultIfEmpty()
    select c
  ).Count();

Answer 3

customers
    .Select(customer => customer.Order)
    .Sum(orders => (orders != null) ? orders.Count() : 1)

Answer 4

如果您想將“無訂單”計為1並計算訂單，則此方法有效：

int customerOrders = customers.Sum(c => c.Orders == null ? 1 : c.Orders.Count());

順便說一句，問題非常典范。

Answer 5

你可能會搜索這樣的東西：

 customers.GroupBy(customer=>customer).  //group by object iyself
        Select(c=>                       //select
                    new  
                    {
                      ID = c.Key.Id,                             
                      Name = c.Key.Name, 
                      Count = (c.Key.Orders!=null)? c.Key.Orders.Count():0
                    }
               );

Answer 6

var orderFreeCustomers = customers.Where(c=>c.Orders== null || c.Orders.Any()==false);

var totalOrders = customers.Where (c => c.Orders !=null).
Aggregate (0,(v,e)=>(v+e.Orders.Count)  );

結果是這兩個值的總和