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?)
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?)
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
}
}
}
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
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};
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?
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);
}
}
}