C# Linq操作List的問題，求教！謝謝~

[h744379120]

初学Linq，对linq操作List不太熟悉，现有以下三点困惑，望各位多多指教：
假设有一个用户类，包括了存款帳號，存款名，存款金額和一个DataTable，简单的代码如下：
static void Main(string[] args)
{
List<user> list = new List<user>();
list.Add(new user() { struserNo = "A1", struserName = "張三", deposit = 10000，dtUser = null});
list.Add(new user() { struserNo = "A1", struserName = "張三", deposit = 20000，dtUser = null});

list.Add(new user() { struserNo = "A2", struserName = "李四", deposit = 30000，dtUser = null});
list.Add(new user() { struserNo = "A2", struserName = "李四", deposit = 40000，dtUser = null});

list.Add(new user() { struserNo = "A3", struserName = "王五", deposit = 44000，dtUser = null});
}
class user
{
public string struserNo { get; set; }//存款帳號
public string struserName { get; set; }//存款名
public int deposit{ get; set; }//存款金額
public DataTable dtUser { get; set; }//一個user的DataTable
}
代码里list.add()了几个用户，如果现在我想做以下三个操作该怎么去写代码呢？
1：取出所有存款帳號(struserNo)为“A1”的存款金額(deposit)之和
2：取出存款金額(deposit)为“40000”并且存款帳號(struserNo)为“A2”的存款名(struserName)
3: 如何在每一次执行list。add()事件之后都为user类里的dtUser(DataTable类型)加上一行struserNo = "存款帳號", struserName = "存款名", deposit = “存款金額”？(即是dtUser = null要如何作修改才能达到第三点要求？)

[h744379120]

1，2两个都是像我想像中的那样。谢谢！请问一下为什么第一句可以直接用Console.WriteLine(q);就能输出了结果：30000，而第二句则需要用
foreach (var sss in q)
{
Console.WriteLine(sss);
}
才能输出结果为：<uname = 李四>呢？第二句可不可以不用foreach就直接输出查询的结果为：李四呢？

[机器人]

[Quote=引用 5 楼 h744379120 的回复:]

1，2两个都是像我想像中的那样。谢谢！请问一下为什么第一句可以直接用Console.WriteLine(q);就能输出了结果：30000，而第二句则需要用
foreach (var sss in q)
{
Console.WriteLine(sss);
}
……
[/Quote]

因为 q 是集合嘛。。

另外，关于问题3，List本身不带通知事件，可以换成BindingList<T>或者ObservableCollection<T>
但从你目前的需求来看，这个DataTable应该是全局的，比如“张三”第2条加进去之后，DataTable里应该有2条记录。

PS:已经有List<T> 何必再用DataTable呢？多此一举嘛

static void Main(string[] args)
{
    var list = new ObservableCollection<user>();
    list.CollectionChanged += new System.Collections.Specialized.NotifyCollectionChangedEventHandler(users_CollectionChanged);
    list.Add(new user { struserNo = "A1", struserName = "張三", deposit = 10000, dtUser = null });
    list.Add(new user { struserNo = "A1", struserName = "張三", deposit = 20000, dtUser = null });

    foreach (var u in list)
        Console.WriteLine(string.Join(",", u.dtUser.Rows[0].ItemArray));

    Console.Read();
}

static void users_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
{
    if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Add)
    {
        var user = (user)e.NewItems[0];
        if (user.dtUser == null)
        {
            user.dtUser = new DataTable();
            user.dtUser.Columns.Add("struserNo");
            user.dtUser.Columns.Add("struserName");
            user.dtUser.Columns.Add("deposit");
            user.dtUser.Rows.Add(user.struserNo, user.struserName, user.deposit);
        }
    }
}

[h744379120]

谢谢porschev和cai5，问题解决了，第三点在你们的答案提示中我也解决了。

[h744379120]

fangxinggood又让我学习到新东西了~感谢！

[五哥]

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;

namespace AAA
{
    class Program
    {
        static void Main(string[] args)
        {
            List<user> list = new List<user>();
            list.Add(new user() { struserNo = "A1", struserName = "張三", deposit = 10000, dtUser = null });
            list.Add(new user() { struserNo = "A1", struserName = "張三", deposit = 20000, dtUser = null });
            list.Add(new user() { struserNo = "A1", struserName = "張三1", deposit = 20000, dtUser = null });
            list.Add(new user() { struserNo = "A1", struserName = "張三2", deposit = 20000, dtUser = null });
            list.Add(new user() { struserNo = "A1", struserName = "張三3", deposit = 20000, dtUser = null });

            list.Add(new user() { struserNo = "A2", struserName = "李四", deposit = 30000, dtUser = null });
            list.Add(new user() { struserNo = "A2", struserName = "李四", deposit = 40000, dtUser = null });
            list.Add(new user() { struserNo = "A2", struserName = "李四1", deposit = 40000, dtUser = null });
            list.Add(new user() { struserNo = "A2", struserName = "李四2", deposit = 40000, dtUser = null });
            list.Add(new user() { struserNo = "A2", struserName = "李四3", deposit = 40000, dtUser = null });
            list.Add(new user() { struserNo = "A3", struserName = "王五", deposit = 44000, dtUser = null });


           
            user u = null;
            double total = 0;
            String struserName = "";
            for (int i = 0; i < list.Count(); i++)
            {
                u = list[i];
                //1：取出所有存款帳號(struserNo)为“A1”的存款金額(deposit)之和
                if (u.struserNo.Equals("A1"))
                {
                    total += u.deposit;
                }

                //2：取出存款金額(deposit)为“40000”并且存款帳號(struserNo)为“A2”的存款名(struserName)
                if (u.struserNo.Equals("A2") && (u.deposit == 40000)) 
                {

                    if (struserName.Equals(""))
                    {
                        struserName = u.struserName;
                    }
                    else {
                        struserName += " , " +  u.struserName;
                    }
                }

                //3，我也不会
            }

           

            Console.WriteLine(total);

            Console.WriteLine(struserName);

            Console.ReadLine();
        }
        class user
        {
            public string struserNo { get; set; }//存款帳號
            public string struserName { get; set; }//存款名
            public int deposit { get; set; }//存款金額
            public DataTable dtUser { get; set; }//一個user的DataTable
        }
    }
}

[五哥]

90000
李四 , 李四1 , 李四2 , 李四3

[porschev]

1.var q = list.Where(o => o.struserNo == "A1").Sum(p => p.deposit);

2.var q = list.Where(o => o.deposit == 40000 && o.struserNo == "A2").First().struserName;

3.第三个没看懂。。。

[porschev]

第二个这么写也可以


var q = from a in list where a.deposit == 40000 && a.struserNo == "A2"
select new {uname = a.struserName};