LinQ的第一天（老规矩：还是案例分析，从简单到难）

static void Main(string[] args)
{
int[] int_array = { 1, 8, 5, 9, 15, 20 };

var filtered = from value in int_array//注意是var，可以帮助我们减少很多麻烦
where value > 4
select value;

Console.WriteLine(filtered.GetType());//System.Linq.Enumerable+<WhereIterator>d__0`1[System.Int32]
foreach (int i in filtered)
{
Console.Write(i + "");//8  5  9  15  20
}
Console.WriteLine();

Console.WriteLine("The Next:");
double[] double_array={1.6,2.5,1.5,7.5};
IEnumerable<double> double_arrayQuery =//标准格式
from value in double_array
where value > 2
select value;
Console.WriteLine(double_arrayQuery.GetType());//System.Linq.Enumerable+<WhereIterator>d__0`1[System.Double]
foreach (double testQuery in double_arrayQuery)
{
Console.Write(testQuery+"");//2.5 7.5
}
}

static void Main(string[] args)
{
int[] int_array = { 1, 8, 5, 9, 15, 20 };

var filtered = from value in int_array//注意是var
where value > 4
orderby value//按默认的规则升序排列
select value;

Console.WriteLine(filtered.GetType());//System.Linq.Enumerable+<WhereIterator>d__0`1[System.Int32]
foreach (int i in filtered)
{
Console.Write(i + "");//5  8  9  15  20
}
Console.WriteLine();

Console.WriteLine("The Next:");
double[] double_array={1.6,2.5,1.5,7.5};
IEnumerable<double> double_arrayQuery =//标准格式
from value in double_array
where value > 2
orderby value descending//降序排列
select value;
Console.WriteLine(double_arrayQuery.GetType());//System.Linq.Enumerable+<WhereIterator>d__0`1[System.Double]
foreach (double testQuery in double_arrayQuery)//注意这里查询的是哪个变量，是SQL的变量
{
Console.Write(testQuery+"");//7.5 2.5
}

string[] names = { "Mr.w","Jack","Angrw"};
Console.WriteLine("The names is :");
foreach (string nametest in names)
{
Console.Write(nametest + "");
}
Console.WriteLine();

IEnumerable<string> names_query =
from name in names
orderby name
select name;
Console.WriteLine("The Orderby of name is :");
foreach (string nametest in names_query)
{
Console.Write(nametest + "");
}
Console.WriteLine();

names_query =
from name in names
orderby name descending
select name;
Console.WriteLine("The Orderby...Descending of name is :");
foreach (string nametest in names_query)
{
Console.Write(nametest + "");
}
Console.WriteLine();
}
The Result:
/*
System.Linq.OrderedEnumerable`2[System.Int32,System.Int32]
5  8  9  15  20
The Next:
System.Linq.OrderedEnumerable`2[System.Double,System.Double]
7.5  2.5  The names is :
Mr.w  Jack  Angrw
The Orderby of name is :
Angrw  Jack  Mr.w
The Orderby...Descending of name is :
Mr.w  Jack  Angrw
*/

static void Main(string[] args)
{
int[] int_array = { 1, 8, 5, 9, 15, 20 };
var filtered = from value in int_array//注意是var
where value > 4
orderby value//按默认的规则升序排列
select value;
Console.WriteLine(filtered.GetType());//System.Linq.Enumerable+<WhereIterator>d__0`1[System.Int32]
Display(filtered, "Int");

double[] double_array={1.6,2.5,1.5,7.5};
IEnumerable<double> double_arrayQuery =//标准格式
from value in double_array
where value > 2
orderby value descending//降序排列
select value;
Console.WriteLine(double_arrayQuery.GetType());//System.Linq.Enumerable+<WhereIterator>d__0`1[System.Double]
Display(double_arrayQuery, "Double");

string[] names = { "Mr.w","Jack","Angrw"};
IEnumerable<string> names_query =
from name in names
orderby name
select name;
Display(names_query,"String-orderby");

names_query =
from name in names
orderby name descending
select name;
Display(names_query, "String-orderby..descending");
}
//为了简化我们写成方法调用
static void Display(IEnumerable<string> string_query, string welcome)  //下面3个方法起到了方法重载作用
{
Console.WriteLine("The {0} is :", welcome);
foreach (string test in string_query)
{
Console.Write(test + "");
}
Console.WriteLine();
}

static void Display(IEnumerable<int> int_query, string welcome)
{
Console.WriteLine("The {0} is :", welcome);
foreach (int test in int_query)
{
Console.Write(test + "");
}

Console.WriteLine();
}

static void Display(IEnumerable<double> double_query, string welcome)
{
Console.WriteLine("The {0} is :", welcome);
foreach (double test in double_query)
{
Console.Write(test + "");
}

Console.WriteLine();
}
The Result:
/*
System.Linq.OrderedEnumerable`2[System.Int32,System.Int32]
The Int is :
5  8  9  15  20
System.Linq.OrderedEnumerable`2[System.Double,System.Double]
The Double is :
7.5  2.5
The String-orderby is :
Angrw  Jack  Mr.w
The String-orderby...descending is :
Mr.w  Jack  Angrw
*/

class Program
{
static void Main(string[] args)
{

Member[] persons ={
new Member(-10m, 21, "jack"),
new Member(25m,25,"An"),
new Member(100m,18,"Mr.w"),
new Member(3000m,27,"deve")
};

Display(persons,"The Array");

var betwtenn100M3000M =
from e in persons
where e.Pay >= 100m && e.Pay <= 3000m
select e;
Display(betwtenn100M3000M, "100m-300m");

var PaySort =
from e in persons
orderby e.Pay  //默认是月薪从小到大
select e;
Display(PaySort,"The Pay Sort");

var AgeSort =
from e in persons
orderby e.age descending  //年龄从大到小
select e;
Display(AgeSort, "The Age Sort");
}

static void Display<T>(IEnumerable<T> T_query, string header)//泛型接口
{
Console.WriteLine("{0}  :", header);

foreach (T test in T_query)
{
Console.WriteLine(test + "");
}
Console.WriteLine();
}
}

class Member//成员
{
private decimal pay;// 月薪
public decimal Pay//月薪属性
{
get { return pay; }
set
{
if (value >= 0m)
{
pay = value;
}

}
}
public string name;//这里如果不是public 外部将无法访问
public  int age;

public Member(decimal monthPay, int member_age, string member_name)
{
name = member_name;
age = member_age;
Pay = monthPay;//注意这里的大写Pay
}

public override string ToString()//重写string类的ToString方法
{
return string.Format("Name is: {0}   Age is:{1}   MonthPay is:{2}",name,age,pay);

}

}
The Result:
/*
The Array  :
Name is: jack   Age is:21   MonthPay is:0
Name is: An   Age is:25   MonthPay is:25
Name is: Mr.w   Age is:18   MonthPay is:100
Name is: deve   Age is:27   MonthPay is:3000

100m-300m  :
Name is: Mr.w   Age is:18   MonthPay is:100
Name is: deve   Age is:27   MonthPay is:3000

The Pay Sort  :
Name is: jack   Age is:21   MonthPay is:0
Name is: An   Age is:25   MonthPay is:25
Name is: Mr.w   Age is:18   MonthPay is:100
Name is: deve   Age is:27   MonthPay is:3000

The Age Sort  :
Name is: deve   Age is:27   MonthPay is:3000
Name is: An   Age is:25   MonthPay is:25
Name is: jack   Age is:21   MonthPay is:0
Name is: Mr.w   Age is:18   MonthPay is:100
*/