Linq離開了聯接，在哪里

Question

i'm learning the book:

LINQ到使用C＃4.0的對象

好吧，我的問題：

我有兩個類： Contact和CallLog 。 看起來像：

public class Contact
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string Email { get; set; }
        public string Phone { get; set; }
        public DateTime DateOfBirth { get; set; }
        public string State { get; set; }
};

public class CallLog
    {
        public string Number { get; set; }
        public int Duration { get; set; }
        public bool Incoming { get; set; }
        public DateTime When { get; set; }
    }

關系： Contact.Phone等於CallLog.Number

兩個類具有方法：SampleData（）。 此方法返回一個帶有聯系人和CallLogs的簡單List <>。

List<Contact> contacts = Contact.SampleData();
List<CallLog> callLogs = CallLog.SampleData();

我的查詢是：每個聯系人要打多少個電話。

var query2 = (from contact in contacts
                         join callLog in callLogs on contact.Phone equals callLog.Number into joined
                         from callLog in joined.Where(p=>p.Incoming == false).DefaultIfEmpty()

                         select new
                         {
                             who = contact.FirstName + " " + contact.LastName + " " + contact.Phone,
                             how_many = callLog != null ? callLogs.Where(s =>s.Number == contact.Phone).Count() : 0
                         }).Select(p=>p).Distinct();
            foreach (var q in query2)
            {
                Console.WriteLine(q.who + " " + q.how_many);
            }

結果：

Tom XXXX 555-555-555通話2次

蘇菲YYYY 333-333-333通話3次

標記ZZZZ 111-111-111通話0次

現在我只選擇傳入== true的callLog：

var query2 = (from contact in contacts
                         join callLog in callLogs.Where(p=>p.Incomming == true) on contact.Phone equals callLog.Number into joined
                         from callLog in joined.Where(p=>p.Incoming == false).DefaultIfEmpty()

                         select new
                         {
                             who = contact.FirstName + " " + contact.LastName + " " + contact.Phone,
                             how_many = callLog != null ? callLogs.Where(s =>s.Number == contact.Phone).Count() : 0
                         }).Select(p=>p).Distinct();
            foreach (var q in query2)
            {
                Console.WriteLine(q.who + " " + q.how_many);
            }

（請查看新query2的第二行），但結果相同：

Tom XXXX 555-555-555通話2次

蘇菲YYYY 333-333-333通話3次

標記ZZZZ 111-111-111通話0次

我該如何解決？

Answer 1

嘗試這個 ：

  var query2 = (from contact in contacts
                                 join callLog in callLogs on contact.Phone equals callLog.Number into joined
                                 from callLog in joined.Where(p=>p.Incoming == true).DefaultIfEmpty()

                                 select new
                                 {
                                     who = contact.FirstName + " " + contact.LastName + " " + contact.Phone,
                                     how_many = callLog != null ? callLogs.Where(s =>s.Number == contact.Phone).Count() : 0
                                 }).Select(p=>p).Distinct();
foreach (var q in query2)
{
  Console.WriteLine(q.who + " " + q.how_many);
}

Answer 2

考慮問題而不是代碼，我認為以下內容可以更好地表達您要執行的操作：

var contacts = new List<Contact>
{
    new Contact { FirstName = "Tom", LastName = "Jones", Phone = "555-555-555" },
    new Contact { FirstName = "Sophie", LastName = "Monk", Phone = "333-333-333" },
    new Contact { FirstName = "Mark", LastName = "Twain", Phone = "111-111-111" }
};

var callLogs = new List<CallLog>
{
    new CallLog { Number = "555-555-555", Incoming = true },
    new CallLog { Number = "555-555-555", Incoming = true },
    new CallLog { Number = "333-333-333", Incoming = true },
    new CallLog { Number = "333-333-333", Incoming = true },
    new CallLog { Number = "333-333-333", Incoming = true }
};

var data = contacts.Select(c => new 
    {
        who = string.Format("{0} {1} {2}", c.FirstName, c.LastName, c.Phone),
        how_many = callLogs.Count(l => l.Number == c.Phone && l.Incoming)
    }).ToList();

data.Dump();

}

public class Contact
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Email { get; set; }
    public string Phone { get; set; }
    public DateTime DateOfBirth { get; set; }
    public string State { get; set; }
}

public class CallLog
{
    public string Number { get; set; }
    public int Duration { get; set; }
    public bool Incoming { get; set; }
    public DateTime When { get; set; }

用Linqpad編寫的示例，直接將其復制/粘貼到編輯器中，您將看到以下輸出：

• 誰怎么樣
• 湯姆·瓊斯555-555-555 2
• 蘇菲和尚333-333-333 3
• 馬克·吐溫111-111-111 0