Linq初級學習（標準查詢操做符的使用和調用)
標準查詢操做符
本文章是我最近學習Linq的一些示例,分享給和我同樣剛開始接觸Linq的朋友們做爲一個參考,由於是初學,確定有不少不足,所以但願你們友善提醒,切勿針鋒相對,我會及時改正的~~
01.投影操做符(Select,SelectMany)
(1)Select操做符對單個序列或者集合中的值進行投影,能夠控制從序列中返回指定的列.
方法語法:
代碼
查詢語法:
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
namespace
ConsoleApplication1
{
class
Program
{
static
void
Main(
string
[] args)
{
//
建立測試數據
User[] users
=
new
User[]{
new
User(){ Id
=
1
, FirstName
=
"
Huang
"
, LastName
=
"
Cong
"
, Age
=
12
},
new
User(){ Id
=
2
, FirstName
=
"
Yang
"
, LastName
=
"
Qiu
"
, Age
=
22
},
new
User(){ Id
=
3
, FirstName
=
"
Cai
"
, LastName
=
"
Zheng
"
, Age
=
18
},
new
User(){ Id
=
4
, FirstName
=
"
Huang
"
, LastName
=
"
Chao
"
, Age
=
32
},
new
User(){ Id
=
5
, FirstName
=
"
Teng
"
, LastName
=
"
Jie
"
, Age
=
12
},
new
User(){ Id
=
6
, FirstName
=
"
Liang
"
, LastName
=
"
Zhi
"
, Age
=
8
}
};
//
使用Select操做符進行投影,對序列只返回First一個列
var query
=
users.Select(u
=>
new
{ u.FirstName });
//
輸出
foreach
(var q
in
query)
Console.WriteLine(q.FirstName);
}
}
class
User
{
public
int
Id {
get
set
; }
public
string
FirstName {
get
set
; }
public
string
LastName {
get
set
; }
public
int
Age {
get
set
; }
public
override
string
ToString()
{
return
String.Format(
"
Id:{0}\tFirstName:{1}\tLastName:{2}\tAge:{3}
"
this
.Id,
this
.FirstName,
this
.LastName,
this
.Age);
}
}
}
var query = from u in users select new { u.FirstName };
(2)SelectMany操做符提供了將多個from子句組合起來的功能,它將每一個對象的結果合併成單個序列.
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
namespace
ConsoleApplication1
{
class
Program
{
static
void
Main(
string
[] args)
{
//
建立測試數據
Names[] owners
=
{
new
Names { FirstName
=
"
Scott, Chris
"
,
Pets
=
new
List
<
string
>
{
"
Yukon
"
"
Fido
"
}},
new
Names { FirstName
=
"
Jason, Steve
"
,
Pets
=
new
List
<
string
>
{
"
Killer
"
"
Fluffy
"
}},
new
Names { FirstName
=
"
John, Joe
"
,
Pets
=
new
List
<
string
>
{
"
Spike
"
"
Tinkerbell
"
}}};
//
使用SelectMany操做符將每一個對象的Pets組合成一個序列
var query
=
owners.SelectMany(owner
=>
owner.Pets);
//
對組合好的Pets進行輸出
foreach
(var q
in
query)
Console.WriteLine(q);
}
}
class
Names
{
public
string
FirstName {
get
set
; }
public
List
<
string
>
Pets {
get
set
; }
}
}
運行結果:
02.限制操做符(Where,OfType)
(1)Where是限制操做符,能夠對序列中的值進行過濾.Where操做符不啓動查詢的執行.但開始對對象進行迭代的時候纔將過濾器應用到數據上.
方法語法:
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
static
void
Main(
string
[] args)
{
//
建立測試數據
List
<
string
>
names
=
new
List
<
string
>
();
names.Add(
"
Scott
"
);
names.Add(
"
Dave
"
);
names.Add(
"
Dave
"
);
names.Add(
"
Steve
"
);
names.Add(
"
Joe
"
);
//
使用Where操做符查詢序列中以S開頭的元素
var query
=
names.Where(n
=>
n.StartsWith(
"
S
"
));
//
對組合好的Pets進行輸出
foreach
(var q
in
query)
Console.WriteLine(q);
}
}
}
查詢語法:
var query = from n in names where n.StartsWith( " S " ) select n;
運行結果:
03 排序操做符(OrderBy,OrderByDescending,ThenBy,ThenByDescending,Reverse)
(1)OrderBy/OrderByDescending操做符能將序列中的返回值按照升序/降序的順序進行排列.
方法語法:
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
static
void
Main(
string
[] args)
{
//
建立測試數據
List
<
string
>
names
=
new
List
<
string
>
();
names.Add(
"
Scott
"
);
names.Add(
"
Dave
"
);
names.Add(
"
Dave
"
);
names.Add(
"
Steve
"
);
names.Add(
"
Joe
"
);
//
使用OrderBy操做符對序列進行排序
var query
=
names.Select(n
=>
n).OrderBy(n
=>
n);
Console.WriteLine(
"
----------------------OrderBy排序----------------------
"
);
foreach
(var q
in
query)
Console.WriteLine(q);
//
使用OrderByDescending操做符對序列進行倒序
query
=
names.Select(n
=>
n).OrderByDescending(n
=>
n);
Console.WriteLine(
"
----------------------OrderByDescending排序----------------------
"
);
foreach
(var q
in
query)
Console.WriteLine(q);
}
}
}
查詢語法:
// 正序
var query = from n in names orderby n select n;
//倒 序
query = from n in names orderby n descending select n;
運行結果:
(2)ThenBy/ThenByDescending操做符可按照次關鍵對序列進行升序/降序排列.
方法語法:
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
class
User
{
public
string
Name {
get
set
; }
public
int
Age {
get
set
; }
}
static
void
Main(
string
[] args)
{
//
建立測試數據
List
<
User
>
users
=
new
List
<
User
>
();
users.Add(
new
User() { Name
=
"
Scott
"
, Age
=
12
});
users.Add(
new
User() { Name
=
"
Scott
"
, Age
=
22
});
users.Add(
new
User() { Name
=
"
Doe
"
, Age
=
11
});
users.Add(
new
User() { Name
=
"
Doe
"
, Age
=
8
});
users.Add(
new
User() { Name
=
"
Scott
"
, Age
=
18
});
users.Add(
new
User() { Name
=
"
Doe
"
, Age
=
24
});
//
使用ThenBy操做符對序列再次進行排序
var query
=
users.Select(u
=>
u).OrderBy(u
=>
u.Name).ThenBy(u
=>
u.Age);
Console.WriteLine(
"
----------------------ThenBy排序----------------------
"
);
foreach
(var q
in
query)
Console.WriteLine(
"
Name:{0}\tAge:{1}
"
, q.Name, q.Age);
//
使用ThenByDescending操做符對序列再次進行排序
query
=
users.Select(u
=>
u).OrderBy(u
=>
u.Name).ThenByDescending(u
=>
u.Age);
Console.WriteLine(
"
----------------------ThenByDescending排序----------------------
"
);
foreach
(var q
in
query)
Console.WriteLine(
"
Name:{0}\tAge:{1}
"
, q.Name, q.Age);
}
}
}
查詢語法:
// 正序
var query = from u in users orderby u.Name, u.Age select u;
// 倒序
query = (from u in users orderby u.Name select u).ThenByDescending(u => u.Age);
運行結果:
(3)Reverse操做符只是簡單的把數據源中的數據按照相反的順序返回.(須要注意的是:Reverse在LINQ To SQL中是不支持的).
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
static
void
Main(
string
[] args)
{
//
建立測試數據
List
<
string
>
names
=
new
List
<
string
>
();
names.Add(
"
Scott
"
);
names.Add(
"
Dave
"
);
names.Add(
"
Dave
"
);
names.Add(
"
Steve
"
);
names.Add(
"
Joe
"
);
//
使用Reverse操做符對序列進行逆序排列
names.Reverse();
foreach
(var q
in
names)
Console.WriteLine(q);
}
}
}
運行結果:
04 聯接操做符(join,GroupJoin)
(1)join操做符相似於T-SQL中的inner join,它能夠將一個數據源與另外一個數據源想聯接,根據兩個數據源中相等的值進行匹配.
方法語法:
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
class
User
{
public
string
Name {
set
get
; }
public
int
RoleId {
set
get
; }
}
class
Role
{
public
int
Id {
get
set
; }
public
string
Name {
get
set
; }
}
static
void
Main(
string
[] args)
{
//
建立測試數據
List
<
User
>
users
=
new
List
<
User
>
();
List
<
Role
>
roles
=
new
List
<
Role
>
();
roles.Add(
new
Role() { Id
=
1
, Name
=
"
Admin
"
});
roles.Add(
new
Role() { Id
=
2
, Name
=
"
Guest
"
});
users.Add(
new
User { RoleId
=
1
, Name
=
"
Scott
"
});
users.Add(
new
User { RoleId
=
1
, Name
=
"
Dave
"
});
users.Add(
new
User { RoleId
=
2
, Name
=
"
Steve
"
});
users.Add(
new
User { RoleId
=
2
, Name
=
"
Joe
"
});
//
查詢出ID爲1的角色下的全部用戶
var query
=
users.Join(roles, u
=>
u.RoleId, r
=>
r.Id, (u, r)
=>
new
{ UserName
=
u.Name, RoleId
=
r.Id, RoleName
=
r.Name }).Where(q
=>
q.RoleId
==
1
);
foreach
(var q
in
query)
Console.WriteLine(
"
UserName:{0}\tRoleId:{1}\tRoleName:{2}
"
, q.UserName, q.RoleId, q.RoleName);
}
}
}
查詢語法:
var query = from r in roles
join u in users on r.Id equals u.RoleId
where r.Id == 1
select new { RoleId = r.Id, RoleName = r.Name, UserName = u.Name };
運行結果:
(2)GroupJoin操做符相似於T-SQL中的INNER JOIN, LEFT OUTER JOIN,返回的是一個層級的結果集
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
class
User
{
public
string
Name {
set
get
; }
public
int
RoleId {
set
get
; }
}
class
Role
{
public
int
Id {
get
set
; }
public
string
Name {
get
set
; }
}
static
void
Main(
string
[] args)
{
//
建立測試數據
List
<
User
>
users
=
new
List
<
User
>
();
List
<
Role
>
roles
=
new
List
<
Role
>
();
roles.Add(
new
Role() { Id
=
1
, Name
=
"
Admin
"
});
roles.Add(
new
Role() { Id
=
2
, Name
=
"
Guest
"
});
users.Add(
new
User { RoleId
=
1
, Name
=
"
Scott
"
});
users.Add(
new
User { RoleId
=
1
, Name
=
"
Dave
"
});
users.Add(
new
User { RoleId
=
2
, Name
=
"
Steve
"
});
users.Add(
new
User { RoleId
=
2
, Name
=
"
Joe
"
});
//
查詢全部角色下的用戶
var query
=
roles.GroupJoin(users, r
=>
r.Id, u
=>
u.RoleId, (role, user)
=>
new
{ RoleId
=
role.Id, RoleName
=
role.Name, Users
=
user.Where(u
=>
u.RoleId
==
role.Id) });
foreach
(var role
in
query)
{
Console.WriteLine(
"
RoleId:{0} RoleName:{1}
"
, role.RoleId, role.RoleName);
foreach
(var user
in
role.Users)
{
Console.WriteLine(
"
"
+
user.Name);
}
}
}
}
}
運行結果:
05 分組操做符(GroupBy)
(1)GroupBy分組操做符是根據一個指定的特定值將序列中的值或元素進行分組.
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
class
User
{
public
string
Name {
set
get
; }
public
int
RoleId {
set
get
; }
}
static
void
Main(
string
[] args)
{
//
建立測試數據
List
<
User
>
users
=
new
List
<
User
>
();
users.Add(
new
User { RoleId
=
1
, Name
=
"
Scott
"
});
users.Add(
new
User { RoleId
=
1
, Name
=
"
Dave
"
});
users.Add(
new
User { RoleId
=
2
, Name
=
"
Steve
"
});
users.Add(
new
User { RoleId
=
2
, Name
=
"
Joe
"
});
//
按RoleId對全部用戶進行分組
var query
=
users.GroupBy(u
=>
u.RoleId);
foreach
(var o
in
query)
{
Console.WriteLine(
"
RoleId:{0}:
"
, o.Key);
foreach
(var user
in
o)
{
Console.WriteLine(
"
Name:{0}
"
, user.Name);
}
}
}
}
}
運行結果:
06 串聯操做符(Concat)
(1)Concat操做符能夠將兩個對象聯接在一塊兒
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
class
User
{
public
string
Name {
set
get
; }
public
int
RoleId {
set
get
; }
}
class
Role
{
public
int
Id {
get
set
; }
public
string
Name {
get
set
; }
}
static
void
Main(
string
[] args)
{
//
建立測試數據
List
<
User
>
users
=
new
List
<
User
>
();
List
<
Role
>
roles
=
new
List
<
Role
>
();
roles.Add(
new
Role() { Id
=
1
, Name
=
"
Admin
"
});
roles.Add(
new
Role() { Id
=
2
, Name
=
"
Guest
"
});
users.Add(
new
User { RoleId
=
1
, Name
=
"
Scott
"
});
users.Add(
new
User { RoleId
=
1
, Name
=
"
Dave
"
});
users.Add(
new
User { RoleId
=
2
, Name
=
"
Steve
"
});
users.Add(
new
User { RoleId
=
2
, Name
=
"
Joe
"
});
//
按全部的用戶名稱和角色名稱聯接起來
var query
=
users.Select(u
=>
u.Name).Concat(roles.Select(r
=>
r.Name));
foreach
(var q
in
query)
{
Console.WriteLine(q);
}
}
}
}
運行結果:
07 聚合操做符(Aggregate,Average,Count,LongCount,Max,Min,Sum)
(1)聚合函數是在序列上執行特定的運算後返回單個值.共有7個聚合查詢操做符:
Aggregate:將序列中的值進行累積並返回結果.
Average:計算一個數值序列的平均值.
Count,LongCount:計算一個集合中元素的個數.可是前者返回的是Int32類型的值,後者爲Int64
Max,Min:分別是返回序列中的最大值和最小值
Sum:返回集合中數值的總和
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
class
User
{
public
string
Name {
set
get
; }
public
int
Age {
set
get
; }
}
static
void
Main(
string
[] args)
{
//
建立測試數據
List
<
User
>
users
=
new
List
<
User
>
();
users.Add(
new
User { Age
=
12
, Name
=
"
Scott
"
});
users.Add(
new
User { Age
=
22
, Name
=
"
Dave
"
});
users.Add(
new
User { Age
=
18
, Name
=
"
Steve
"
});
users.Add(
new
User { Age
=
24
, Name
=
"
Joe
"
});
string
Names
=
"
Scott,Dave,Steve,Joe
"
;
string
[] name
=
Names.Split(
'
,
'
);
Console.WriteLine(
"
使用Aggregate將名稱組合起來:
"
);
string
query1
=
name.Aggregate((n, next)
=>
n
+
"
"
+
next);
Console.WriteLine(query1);
Console.WriteLine(
"
------------------------------------------------
"
);
Console.WriteLine(
"
使用Average求出全部用戶年齡的平均數:
"
);
var query2
=
users.Select(u
=>
u.Age).Average();
Console.WriteLine(query2);
Console.WriteLine(
"
------------------------------------------------
"
);
Console.WriteLine(
"
使用Count求出總共有多少個用戶:
"
);
var query3
=
users.Count();
Console.WriteLine(query3);
Console.WriteLine(
"
------------------------------------------------
"
);
Console.WriteLine(
"
使用LongCount求出全部用戶年齡的平均數:
"
);
var query4
=
users.LongCount();
Console.WriteLine(query4);
Console.WriteLine(
"
------------------------------------------------
"
);
Console.WriteLine(
"
使用Max求出全部用戶年齡的最大數:
"
);
var query5
=
users.Select(u
=>
u.Age).Max();
Console.WriteLine(query5);
Console.WriteLine(
"
------------------------------------------------
"
);
Console.WriteLine(
"
使用Min求出全部用戶年齡的最小數:
"
);
var query6
=
users.Select(u
=>
u.Age).Min();
Console.WriteLine(query6);
Console.WriteLine(
"
------------------------------------------------
"
);
Console.WriteLine(
"
使用Sum求出全部用戶年齡的總和:
"
);
var query7
=
users.Select(u
=>
u.Age).Sum();
Console.WriteLine(query7);
Console.WriteLine(
"
------------------------------------------------
"
);
}
}
}
運行結果:
08 集合操做符(Distinct,Union,Intersect,Except)
(1)Distinct操做符能夠刪除集合中重複的值,並返回該集合中不相同的元素.
代碼
運行結果:
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
static
void
Main(
string
[] args)
{
//
建立測試數據
int
[] numbers
=
new
int
[] {
1
1
1
2
3
4
5
5
};
//
使用Distinct將數組中重複的元素刪除掉
var query
=
numbers.Distinct();
foreach
(var q
in
query)
{
Console.WriteLine(query);
}
}
}
}
(2)Union操做符能夠取兩個集合的互不相同的全部數值.
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
static
void
Main(
string
[] args)
{
//
建立測試數據
int
[] numbers1
=
new
int
[] {
1
1
1
2
3
4
5
5
};
int
[] numbers2
=
new
int
[] {
2
2
3
4
4
5
6
7
};
//
使用Union將兩個數組中重複的元素刪除掉而且合併起來
var query
=
numbers1.Union(numbers2);
foreach
(var q
in
query)
{
Console.WriteLine(q);
}
}
}
}
運行結果:
(3)Intersect操做符能夠返回兩個序列的交集.也就是返回同時存在於2個序列中的值.
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
static
void
Main(
string
[] args)
{
//
建立測試數據
int
[] numbers1
=
new
int
[] {
1
1
1
2
3
4
5
5
};
int
[] numbers2
=
new
int
[] {
2
2
3
4
4
5
6
7
};
//
使用Intersect求兩個集合的交集
var query
=
numbers1.Intersect(numbers2);
foreach
(var q
in
query)
{
Console.WriteLine(q);
}
}
}
}
運行結果:
(4)Except操做符能夠返回兩個序列中不一樣的值.
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
static
void
Main(
string
[] args)
{
//
建立測試數據
int
[] numbers1
=
new
int
[] {
1
1
1
2
3
4
5
5
};
int
[] numbers2
=
new
int
[] {
2
2
3
4
4
5
6
7
};
//
使用Except求numbers1中有可是numbers2中沒有的值
var query
=
numbers1.Except(numbers2);
foreach
(var q
in
query)
{
Console.WriteLine(q);
}
}
}
}
運行結果:
09 生成操做符(Empty,Range,Repeat)
(1)Empty操做符能夠返回一個指定類型的空集,一般用來做爲聚合操做符的種子值.
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
static
void
Main(
string
[] args)
{
//
建立測試數據
int
[] numbers1
=
new
int
[] {
1
2
3
4
5
};
int
[] numbers2
=
new
int
[] {
4
5
6
7
};
List
<
int
[]
>
numbers
=
new
List
<
int
[]
>
{ numbers1, numbers2 };
//
建立一個空int類型的集合
var empty
=
Enumerable.Empty
<
int
>
();
//
求numbers1和numbers2中有7這個元素的集合,並輸出具有條件的集合
var query
=
numbers.Aggregate(empty, (n, next)
=>
next.Contains(
7
?
n.Union(next) : n);
foreach
(var q
in
query)
{
Console.WriteLine(q);
}
}
}
}
運行結果:
(2)Range操做符能夠建立一個連續數字序列的集合.
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
static
void
Main(
string
[] args)
{
Console.WriteLine(
"
建立一個1~6的數值集合
"
);
var numbers
=
Enumerable.Range(
1
6
);
foreach
(var q
in
numbers)
{
Console.WriteLine(q);
}
Console.WriteLine(
"
--------------------------------------
"
);
Console.WriteLine(
"
倒序
"
);
var query
=
numbers.Reverse();
foreach
(var q
in
query)
{
Console.WriteLine(q);
}
Console.WriteLine(
"
--------------------------------------
"
);
Console.WriteLine(
"
輸出1~6的偶數
"
);
query
=
numbers.Where(u
=>
u
%
2
==
0
);
foreach
(var q
in
query)
{
Console.WriteLine(q);
}
Console.WriteLine(
"
--------------------------------------
"
);
}
}
}
運行結果:
(3)Repeat操做符能夠建立一個單值序列,可自定義重複的次數.
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
static
void
Main(
string
[] args)
{
//
將Good!重複6次
var numbers
=
Enumerable.Repeat(
"
Good!
"
6
);
foreach
(var q
in
numbers)
{
Console.WriteLine(q);
}
}
}
}
運行結果:
10 轉換操做符(Cast,OfType,ToArray,ToList,ToLookup)
(1)Cast操做符將查詢能夠將IEnumerable中的元素轉換爲指定的類型.
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
static
void
Main(
string
[] args)
{
//
建立測試數據
ArrayList names
=
new
ArrayList();
names.Add(
"
Scott
"
);
names.Add(
"
Dave
"
);
names.Add(
"
Steve
"
);
names.Add(
"
Joe
"
);
//
ArrayList不實現IEnumberable(Of T),不可使用標準查詢操做符,
//
可是經過Cast轉換以後就可使用了
var query
=
names.Cast
<
string
>
().Select(u
=>
u);
foreach
(var q
in
query)
{
Console.WriteLine(q);
}
}
}
}
運行結果:
(2)OfType操做符能夠對一個序列進行指定類型的過濾.
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
static
void
Main(
string
[] args)
{
//
建立測試數據
ArrayList names
=
new
ArrayList();
names.Add(
"
Scott
"
);
names.Add(
1
);
names.Add(
"
Dave
"
);
names.Add(
2
);
names.Add(
"
Steve
"
);
names.Add(
3
);
names.Add(
"
Joe
"
);
//
經過OfType能夠過濾只能轉換爲int類型的元素
var query
=
names.OfType
<
int
>
().Select(u
=>
u);
foreach
(var q
in
query)
{
Console.WriteLine(q);
}
}
}
}
運行結果:
(3)ToArray/ToList操做符能夠分別能夠將序列建立爲一個數組或者List<T>對象.須要注意的是進行轉換時會強制查詢當即執行,也就意味着查詢將於源數據斷開聯繫.獲得的序列爲新建立的數組或List<T>.
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
static
void
Main(
string
[] args)
{
//
建立測試數據
List
<
string
>
names
=
new
List
<
string
>
();
names.Add(
"
Scott
"
);
names.Add(
"
Dave
"
);
//
轉換爲Array或者List
var query1
=
names.Select(u
=>
u).ToArray();
var query2
=
names.Select(u
=>
u).ToList();
Console.WriteLine(
"
ToArray:
"
);
foreach
(var q
in
query1) { Console.WriteLine(
"
"
+
q); }
Console.WriteLine(
"
ToList:
"
);
foreach
(var q
in
query2) { Console.WriteLine(
"
"
+
q); }
Console.WriteLine(
"
---------------------------------------------
"
);
//
添加新元素
names.Add(
"
Steve
"
);
names.Add(
"
Joe
"
);
//
再次輸出,可是並無後面添加的元素,說明查詢與源數據已斷開聯繫
Console.WriteLine(
"
ToArray:
"
);
foreach
(var q
in
query1) { Console.WriteLine(
"
"
+
q); }
Console.WriteLine(
"
ToList:
"
);
foreach
(var q
in
query2) { Console.WriteLine(
"
"
+
q); }
}
}
}
運行結果:
(4)ToDictionary/ToLookUp能夠將序列分別轉換爲一對一的Dictionary<T Key,T Value>字典,或者一對多的LookUp<T Key,TElement Values>字典.
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
class
User
{
public
int
Id {
set
get
; }
public
string
Name {
set
get
; }
}
static
void
Main(
string
[] args)
{
//
建立測試數據
List
<
User
>
users
=
new
List
<
User
>
();
users.Add(
new
User { Id
=
1
, Name
=
"
Scott
"
});
users.Add(
new
User { Id
=
2
, Name
=
"
Scott
"
});
users.Add(
new
User { Id
=
3
, Name
=
"
Doe
"
});
users.Add(
new
User { Id
=
4
, Name
=
"
Doe
"
});
Dictionary
<
int
, User
>
query1
=
users.ToDictionary(u
=>
u.Id);
ILookup
<
string
, User
>
query2
=
users.ToLookup(u
=>
u.Name);
Console.WriteLine(
"
ToDictionary示例:
"
);
foreach
(var q
in
query1)
{
Console.WriteLine(
"
Key:{0}\tUserName:{1}
"
, q.Key, q.Value.Name);
}
Console.WriteLine(
"
-------------------------------------------------
"
);
Console.WriteLine(
"
ToLookup示例:
"
);
foreach
(var q
in
query2)
{
Console.WriteLine(
"
Key:{0}
"
, q.Key);
foreach
(var item
in
q)
{
Console.WriteLine(
"
\tUserId:{0}\tUserName:{1}
"
, item.Id, item.Name);
}
}
}
}
}
運行結果:
11 元素操做符(DefaultIfEmpty,ElementAt,ElementAtOrDefault,First,Last,FirstOrDefault,LastOrDefault,Single,SingleOrDefault)
(1)DefaultIfEmpty操做符將一個空集合替換爲包含默認值的集合.
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
class
User
{
public
int
Id {
set
get
; }
public
string
Name {
set
get
; }
}
static
void
Main(
string
[] args)
{
//
建立測試數據
List
<
User
>
users
=
new
List
<
User
>
();
//
若是沒有任何用戶信息,返回一個默認值
var query
=
users.DefaultIfEmpty(
new
User() { Id
=
0
, Name
=
"
None
"
});
foreach
(var q
in
query)
{
Console.WriteLine(
"
UserId:{0}\tUserName:{1}
"
, q.Id, q.Name);
}
}
}
}
運行結果:
(2)ElementAt操做符返回集合中給定索引處的元素,若是索引超出範圍則會拋出一個index out of range的錯誤,若是不能肯定索引範圍,應使用ElementAtOrDefault操做符,ElementAtOrDefault操做符會在索引超出範圍時返回一個默認值.
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
class
User
{
public
int
Id {
set
get
; }
public
string
Name {
set
get
; }
}
static
void
Main(
string
[] args)
{
//
建立測試數據
string
[] names
=
new
string
[] {
"
Scott
"
"
Dave
"
"
Steve
"
"
Joe
"
};
string
name1
=
names.ElementAt(
1
);
string
name2
=
names.ElementAtOrDefault(
8
);
//
返回索引爲1的元素
Console.WriteLine(name1);
//
操做範圍,返回默認值null,若是爲數值類型返回0
Console.WriteLine(name2);
}
}
}
運行結果:
(3)First/Last操做符分別是返回集合中的第一個/最後一個元素,若是不肯定是否有第一個或者最後一個值,可使用FirstOrDefaule/LastOrDefault,它們分別會在First/Last操做符找不到元素的時候返回默認值.
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
class
User
{
public
int
Id {
set
get
; }
public
string
Name {
set
get
; }
}
static
void
Main(
string
[] args)
{
//
建立測試數據
string
[] names
=
new
string
[] {
"
Scott
"
"
Dave
"
"
Steve
"
"
Joe
"
};
//
返回索引爲0的元素
string
name1
=
names.First();
//
返回索引爲0,而且首字母爲T的元素,若是沒有則返回默認值null
string
name2
=
names.FirstOrDefault(u
=>
u.StartsWith(
"
T
"
));
//
返回集合中最後一個元素
string
name3
=
names.Last();
//
返回集合中最後一個,而且首字母爲T的元素,若是沒有則返回默認值null
string
name4
=
names.LastOrDefault(u
=>
u.StartsWith(
"
T
"
));
Console.WriteLine(name1);
Console.WriteLine(name2);
Console.WriteLine(name3);
Console.WriteLine(name4);
}
}
}
運行結果:
(4)Single操做符能夠從一個序列中返回惟一知足某個特定條件的元素,若是找不到匹配的元素或者序列返回多個符合條件的元素,都會拋出異常.若是但願找不到元素時返回一個默認值,可使用SingleOrDefault操做符.
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
class
User
{
public
int
Id {
set
get
; }
public
string
Name {
set
get
; }
}
static
void
Main(
string
[] args)
{
//
建立測試數據
string
[] names
=
new
string
[] {
"
Scott
"
"
Dave
"
"
Steve
"
"
Joe
"
};
//
返回集合中以D爲首字母的元素
string
name1
=
names.Single(s
=>
s.StartsWith(
"
D
"
));
//
返回集合中以O爲首字母的元素,若是沒有則返回默認值null
string
name2
=
names.SingleOrDefault(s
=>
s.StartsWith(
"
O
"
));
Console.WriteLine(name1);
Console.WriteLine(name2);
}
}
}
運行結果:
12 相等操做符(SequenceEqual)
(1)SequenceEqual操做符能夠斷定兩個集合是否相等,返回值爲Boolean值.
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
static
void
Main(
string
[] args)
{
//
建立測試數據
List
<
string
>
names1
=
new
List
<
string
>
{
"
Scott
"
"
Dave
"
"
Steve
"
"
Joe
"
};
List
<
string
>
names2
=
new
List
<
string
>
{
"
Scott
"
"
Dave
"
"
Steve
"
"
Joe
"
};
bool
equal1
=
names1.SequenceEqual(names2);
names1.Add(
"
add
"
);
bool
equal2
=
names1.SequenceEqual(names2);
Console.WriteLine(equal1);
Console.WriteLine(equal2);
}
}
}
運行結果:
13 量詞操做符(All,Any)
(1)All操做符判斷集合中全部元素是否知足特定的條件.若是均知足返回True,不然False.
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
static
void
Main(
string
[] args)
{
//
建立測試數據
List
<
string
>
names1
=
new
List
<
string
>
{
"
Scoet
"
"
Dave
"
"
Steve
"
"
Joe
"
};
//
是否均包含字母e
bool
all1
=
names1.All(u
=>
u.Contains(
"
e
"
));
//
是否均以字母e開頭
bool
all2
=
names1.All(u
=>
u.StartsWith(
"
e
"
));
Console.WriteLine(all1);
Console.WriteLine(all2);
}
}
}
運行結果:
(2)Any操做符判斷集合中是否至少有一個元素知足特定的條件.有則返回True,不然False.
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
static
void
Main(
string
[] args)
{
//
建立測試數據
List
<
string
>
names1
=
new
List
<
string
>
{
"
Scoet
"
"
Dave
"
"
Steve
"
"
Joe
"
};
//
是否至少有一個元素是以D開頭的
bool
all1
=
names1.Any(u
=>
u.StartsWith(
"
D
"
));
//
是否至少有一個元素包含字母i
bool
all2
=
names1.All(u
=>
u.Contains(
"
i
"
));
Console.WriteLine(all1);
Console.WriteLine(all2);
}
}
}
運行結果:
14 分割操做符(Skip,SkipWhile,Take,TakeWhile)
(1)Skip操做符會跳過指定數量的元素後返回餘下的元素,SkipWhile操做符則會經過特定的條件跳過一些元素,而後返回餘下的元素.
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
static
void
Main(
string
[] args)
{
//
建立測試數據
List
<
int
>
numbers
=
new
List
<
int
>
{
23
4
55
190
5
54
70
};
//
跳過前面3個元素,返回餘下的元素
var query1
=
numbers.Skip(
3
);
//
跳過前面不知足"大於50"這個條件的,返回餘下的元素
var query2
=
numbers.SkipWhile(u
=>
u
<
50
);
foreach
(var q
in
query1)
{
Console.WriteLine(q);
}
Console.WriteLine(
"
----------------------------------------
"
);
foreach
(var q
in
query2)
{
Console.WriteLine(q);
}
}
}
}
運行結果:
(2)Take操做符會返回集合前面指定數量的元素,TakeWhile操做符則會經過特定的條件選取元素,若是某個元素不符合條件,則從該元素起的元素所有跳過.
代碼
//
-----------------------------------------------------------
//
All Rights Reserved , Copyright (C) 2010 ,黃聰 , Ltd .
//
-----------------------------------------------------------
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
using
System.Data.Linq;
using
System.Collections;
namespace
ConsoleApplication1
{
class
Program
{
static
void
Main(
string
[] args)
{
//
建立測試數據
List
<
int
>
numbers
=
new
List
<
int
>
{
23
4
55
190
5
54
70
};
//
獲取前面3個元素
var query1
=
numbers.Take(
3
);
//
獲取知足"小於50"這個條件的元素,只要有哪一個不知足,則從該元素起的元素所有忽略
var query2
=
numbers.TakeWhile(u
=>
u
<
50
);
foreach
(var q
in
query1)
{
Console.WriteLine(q);
}
Console.WriteLine(
"
----------------------------------------
"
);
foreach
(var q
in
query2)
{
Console.WriteLine(q);
}
}
}
}
運行結果:
小結
標準查詢操做符是LINQ查詢表達式的構成模塊,它們提供了許多查詢功能,目前我正在自學這些內容,在此把本身的學習成果分享一下,僅提供給初學者做爲參考用,若是有錯誤的地方請高手指出,我儘快改正~~
做者：小聰崽的一切
出處：http://www.cnblogs.com/huangcong/
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