C# 实体框架Linq、左连接和具有总和和计数的组

我需要一些帮助来将SQL转换为Linq。在MySQL中它非常简单

Table: customers
ID  Name    
1   Bill
2   John

Table: purchases
ID  CustomerID  CompletedTransaction
1   1           False
2   2           True
3   1           True
4   1           True


    SELECT  c.ID
        c.Name,
        COUNT(p.ID) AS TotalPurchases,
        SUM(CASE WHEN p.CompletedTransaction = TRUE THEN 1 ELSE 0 END) AS                       TotalCompleted
    FROM customers c
    LEFT JOIN purchases p ON c.ID = p.CustomerID
    GROUP BY c.ID

Expected Result:
1, Bill, 3, 2
2, John, 1, 1

我已经看到了一些关于如何在Linq中实现左连接的示例，但我不确定如何在其中包含求和和计数。我在Linq中看到过一些示例，其中返回的字段是从组键中选择的。这是否意味着如果我在customers表中有更多的字段，例如我想返回的地址和其他联系方式，我必须将它们包括在联接中，然后才能选择它们？希望这是有意义的。感谢任何可能为我指明正确方向的帮助或链接

谢谢

这是样品

class Program
    {
        static void Main(string[] args)
        {

            List<Customers> customers = new List<Customers>();
            customers.Add(new Customers() { ID = 1, Name = "Bill" });
            customers.Add(new Customers() { ID = 2, Name = "John" });

            List<Purchases> purchases = new List<Purchases>();
            purchases.Add(new Purchases() { ID = 1, CustomerID = 1, CompletedTransaction = false });
            purchases.Add(new Purchases() { ID = 2, CustomerID = 2, CompletedTransaction = true });
            purchases.Add(new Purchases() { ID = 3, CustomerID = 1, CompletedTransaction = true });
            purchases.Add(new Purchases() { ID = 4, CustomerID = 1, CompletedTransaction = true });

            IEnumerable<JoinResult> results = from c in customers
                                       join p in purchases
                                       on c.ID equals p.CustomerID
                                       group new { c, p } by new {p.CustomerID, c.Name} into r
                                       select new JoinResult
                                       {
                                           CustomerID = r.Key.CustomerID,
                                           CustomerName = r.Key.Name,
                                           TotalPurchases = r.Count(),
                                           TotalCompleteTransaction = r.Where(s=> s.p.CompletedTransaction).Count()
                                       };

            foreach(JoinResult r in results)
            {
                Console.WriteLine($"CustomerID : {r.CustomerID} | Name : {r.CustomerName} | TotalPurchases : {r.TotalPurchases} | TotalCompleteTransaction : {r.TotalCompleteTransaction}");
            }

            Console.ReadKey();
        }
    }

    class Customers
    {
        public int ID { get; set; }
        public string Name { get; set; }
    }

    class Purchases
    {
        public int ID { get; set; }
        public int CustomerID { get; set; }
        public bool CompletedTransaction { get; set; }
    }

    class JoinResult
    {
        public int CustomerID { get; set; }
        public string CustomerName { get; set; }
        public int TotalPurchases { get; set; }
        public int TotalCompleteTransaction { get; set; }
    }

类程序
{
静态void Main（字符串[]参数）
{
列出客户=新列表（）；
添加（新客户（）{ID=1，Name=“Bill”}）；
添加（新客户（）{ID=2，Name=“John”}）；
列表购买=新列表（）；
Add（new purchases（）{ID=1，CustomerID=1，CompletedTransaction=false}）；
Add（new purchases（）{ID=2，CustomerID=2，CompletedTransaction=true}）；
Add（new purchases（）{ID=3，CustomerID=1，CompletedTransaction=true}）；
Add（new purchases（）{ID=4，CustomerID=1，CompletedTransaction=true}）；
IEnumerable结果=来自客户中的c
参与采购
在c.ID上等于p.CustomerID
通过new{p.CustomerID，c.Name}将new{c，p}分组到r中
选择新结果
{
CustomerID=r.Key.CustomerID，
CustomerName=r.Key.Name，
TotalPurchases=r.Count（），
TotalCompleteTransaction=r.Where（s=>s.p.CompletedTransaction）.Count（）
};
foreach（结果中的JoinResult）
{
Console.WriteLine（$“CustomerID:{r.CustomerID}名称：{r.CustomerName}总计采购：{r.TotalPurchases}总计采购：{r.TotalCompleteTransaction}”）；
}
Console.ReadKey（）；
}
}
类客户
{
公共int ID{get；set；}
公共字符串名称{get；set；}
}
班级购买
{
公共int ID{get；set；}
public int CustomerID{get；set；}
public bool CompletedTransaction{get；set；}
}
类连接结果
{
public int CustomerID{get；set；}
公共字符串CustomerName{get；set；}
公共整数{get；set；}
公共int TotalCompleteTransaction{get；set；}
}

结果

---

感谢您的帮助，尽管看起来这是一个内部连接，而不是左连接。

var answer = (from c in db.customers 
              join p in db.purchases 
              on c.ID = p.CustomerID into subs
              from sub in subs.DefaultIfEmpty()
              group sub by new { c.ID, c.Name } into gr
              select new {
                  gr.Key.ID,
                  gr.Key.Name,
                  Total = gr.Count(x => x != null),
                  CountCompleted = gr.Count(x => x != null && x.CompletedTransaction)
              }).ToList();