LINQ中扁平化的父母子女协会的数量

Question

我想算一些没有孩子的父母和父母的孩子.在我写这篇文章时,我意识到用代码更好地解释了..所以,这里有:

使用以下示例类型:

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; }
}

这个数据:

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

我试图得到3回.

预先感谢您的帮助.

-Jessy Houle

之后添加:

所有伟大(和快速)的答案让我印象深刻.对于其他人来到这个问题,寻找一些选项,这里是一个单元测试,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,谢谢大家的帮助!

Answer 1

怎么样

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