LINQ的左连接并在

Question

i'm learning the book: 

LINQ到使用C＃4.0

好对象，我的问题：

我有两个类：联系和CallLog。它看起来像：

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; } 
    } 

关系：Contact.Phone等于CallLog.Number

二班有方法：sampleData在（）。这个metod返回一个简单的列表<>与联系人和通话记录。

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

我的查询是：每个联系人有多少个呼叫。

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); 
      } 

结果：

汤姆XXXX 555-555-555调用2次

苏菲YYYY 333-333-333调用3次

马克ZZZZ 111-111-111电话0次

现在我想只选择callLog Incoming == true：

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); 
      } 

（看看新QUERY2第二线） 但结果是一样的：

汤姆XXXX 555-555-555调用2次

苏菲YYYY 333-333-333调用3次

Mark ZZZZ 111-111-111要求0次

我该如何解决它？

Answer 1

试试这个：

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

的问题，而不是看代码，我认为下面更好的表达你想要做什么：写在Linqpad

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; } 

样品，复制/它直接粘贴到编辑器，你应该看到下面的输出：

• 谁HOW_MANY
• 汤姆·琼斯555-555-555 2
• 索菲·蒙克333-333-333 3
• 马克·吐温111-111-111 0