[英]Linq left join and where
i'm learning the book:
LINQ to Objects Using C# 4.0 LINQ到使用C#4.0的对象
Ok, my question: 好吧,我的问题:
I have two class: Contact and CallLog . 我有两个类: Contact和CallLog 。 It look like: 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; }
}
Relation: Contact.Phone equals CallLog.Number 关系: Contact.Phone等于CallLog.Number
Two Class have method: SampleData(). 两个类具有方法:SampleData()。 This metod return a simple List<> with Contacts and CallLogs. 此方法返回一个带有联系人和CallLogs的简单List <>。
List<Contact> contacts = Contact.SampleData();
List<CallLog> callLogs = CallLog.SampleData();
My query is: how many calls do each contact. 我的查询是:每个联系人要打多少个电话。
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);
}
the result: 结果:
Tom XXXX 555-555-555 calls 2 times Tom XXXX 555-555-555通话2次
Sophie YYYY 333-333-333 calls 3 times 苏菲YYYY 333-333-333通话3次
Mark ZZZZ 111-111-111 calls 0 times 标记ZZZZ 111-111-111通话0次
Now i want to choose only callLog where Incoming == true: 现在我只选择传入== 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);
}
(look at the second line in new query2) but result is same: (请查看新query2的第二行),但结果相同:
Tom XXXX 555-555-555 calls 2 times Tom XXXX 555-555-555通话2次
Sophie YYYY 333-333-333 calls 3 times 苏菲YYYY 333-333-333通话3次
Mark ZZZZ 111-111-111 calls 0 times 标记ZZZZ 111-111-111通话0次
how could i fix it? 我该如何解决?
Try this : 尝试这个 :
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);
}
Looking at the problem instead of the code, I think the following better expresses what you're trying to do: 考虑问题而不是代码,我认为以下内容可以更好地表达您要执行的操作:
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; }
Sample written in Linqpad, copy/paste it straight into the editor and you should see the following output: 用Linqpad编写的示例,直接将其复制/粘贴到编辑器中,您将看到以下输出:
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