C# LINQ 转换查询语法扩展

Question

如何将以下 LINQ 查询语法转换为具有 Lambda 表达式的扩展语法？我正在尝试从第 11.3.9 章的伽利略计算开放书 C#2012 中学习。 以下是使用的类:

public class Customer
{   public string Name { get; set; }
    public List<Order> Orders { get; set; }
}
public class Order
{   public int OrderID { get; set; }
    public int ProductID { get; set; }
    public int Quantity { get; set; }
}
public class Product
{   public int ProductID { get; set; }
    public double Price { get; set; }
}

在 customerList 中有一些“Customer”对象，在 Orders 属性中您可以找到“Order”对象的列表。 这是我想用 lambda 表达式编写的代码:

 var allOrders =
       from cust in customerList
       from ord in cust.Orders
       join prod in productList on ord.ProductID equals prod.ProductID
       select new
       {
           cust.Name,
           ord.ProductID,
           OrderAmount = ord.Quantity * prod.Price
       };

 var summe =
       from cust in customerList
       join ord in allOrders
       on cust.Name equals ord.Name into custWithOrd
       select new { cust.Name, TotalSumme = custWithOrd.Sum(s => s.OrderAmount) };

我想我应该使用 GroupJoin 但我不知道如何在没有任何“from”的情况下编写它 如果你能给我看看就好了。

Answer 1

翻译的两个查询:

var allOrders2 = customerList.SelectMany(cust => cust.Orders, 
                                         (cust, ord) => new
                                         {
                                            cust,
                                            ord
                                         })
                              .Join(productList, 
                                    x => x.ord.ProductID, 
                                    prod => prod.ProductID, 
                                    (x, prod) => new
                                    {
                                        Name = x.cust.Name,
                                        ProductID = x.ord.ProductID,
                                        OrderAmount = (double)x.ord.Quantity * prod.Price
                                    });
var summe2 = customerList.GroupJoin(allOrders, 
                                    cust => cust.Name, 
                                    ord => ord.Name, 
                                    (cust, custWithOrd) => new
                                    {
                                        Name = cust.Name,
                                        TotalSumme = custWithOrd.Sum(s => s.OrderAmount)
                                    });