Linq规范查询操作符
言语集查询 Ganmge hteg.ratedQuw,LINQ,集 成了C#编程言语中的查询语法 ,可 以用雷同的语法接见差别的数据源。 LINQ提 供了差别数据源的笼统层 ,所 以能够运用雷同的语法。
1挑选操作符
挑选操作符定义了返回元素的前提。
| 挑选操作符 | 形貌 |
|---|---|
| where | 运用谓词，返回布尔值 |
| OfType< TResult> | 依据范例挑选元素 |
运用举例：
where用法：
var racers = from r in Formulal.Racers where r.Wins > 15 && r.Country == "Brazil" select r;
OfType< T>用法：
object[] data = {"one", 2, "three", 4, 5, "six"};
var rtnData = data.OfType<string>(); //返回范例为string的数据元素鸠合
2投射操作符
把对象转化为另一个范例的新对象
| 投射操作符 | 形貌 |
|---|---|
| select | |
| selectMany |
用法举例：
select用法
var racers = from r in Formulal.Racers
where r.Wins > 15 && r.Country == "Brazil"
select new
{
Name = string.Format("{0} {1}", r.FirstName, r.LastName),
Country = r.Country,
Wins = r.Wins
}; //输出为含有Name,Country,Wins总计3个属性的对象鸠合
selectMany用法
var ferrariDrivers = Formulal.Racers.
SelectMany(r => r.Cars,
(r, c) => new { Racer = r, Car = c }).
Where(r => r.Car == "Ferrari").
OrderBy(r => r.Racer.LastName).
Select(r => r.Racer.FirstName + " " + r.Racer.LastName);//挑选出驾驶法拉利的选手鸠合
3排序操作符
转变返回元素的递次
| 排序操作符 | 形貌 |
|---|---|
| OrderBy | 升序排序 |
| OrderByDescending | 降序排序 |
| ThenBy | 第一次排序效果相似，用第二次升序排序 |
| ThenByDescending | 第一次排序效果相似，用第二次降序排序 |
| Reverse | 反转鸠合中元素的递次 |
举例：
var racers = from r in Formulal.Racers
where r.Country == "Brazil"
orderby r.Wins descending
select new
{
Name = string.Format("{0} {1}", r.FirstName, r.LastName),
Country = r.Country,
Wins = r.Wins
};//国度为巴西，根据胜场次数降序分列
4衔接运算符
用于兼并不直接相干的鸠合
| 衔接运算符 | 形貌 |
|---|---|
| Join | 能够依据键选择器函数衔接衔接2个鸠合 |
| GroupJoin | 衔接两个鸠合,组合其效果 |
//Join衔接
//猎取冠军年份在2003年后的选手
var racer5 = from r in Formulal.Racers
from y in r.Years
where y > 2003
select new
{
Year = y,
Name = string.Format("{0} {1}", r.FirstName, r.LastName)
}; //猎取冠军年份在2003年后的团队
var team1 = from r in Formulal.ChampionTeams
from y in r.Years
where y > 2003
select new
{
Year = y,
Name = string.Format("{0}", r.Name)
}; //衔接
var racerAndTeams = from r in racer5
join t in team1 on r.Year equals t.Year
select new
{
Yearj= r.Year,
Racerj = r.Name,
Teamj = t.Name
};
效果：
| Yearj | Racerj | Teamj |
|---|---|---|
| Yearj=2004 | Racerj=Michael Schumacher | Teamj =Ferrari |
| Yearj=2005 | Racerj=Fernando Alonso | Teamj =Renault |
| Yearj=2006 | Racerj=Fernando Alonso | Teamj =Renault |
| Yearj=2007 | Racerj=Kimi Räikkönen | Teamj =Ferrari |
| Yearj=2008 | Racerj=Lewis Hamilton | Teamj =Ferrari |
| Yearj=2014 | Racerj=Lewis Hamilton | Teamj =Mercedes |
| Yearj=2015 | Racerj=Lewis Hamilton | Teamj =Mercedes |
| Yearj=2009 | Racerj=Jenson Button | Teamj =Brawn GP |
| Yearj=2010 | Racerj=Sebastian Vettel | Teamj =Red Bull Racing |
| Yearj=2011 | Racerj=Sebastian Vettel | Teamj =Red Bull Racing |
| Yearj=2012 | Racerj=Sebastian Vettel | Teamj =Red Bull Racing |
| Yearj=2013 | Racerj=Sebastian Vettel | Teamj =Red Bull Racing |
5组合运算符
把数据放在组中
| 组合运算符 | 形貌 |
|---|---|
| GroupBy | 组合有大众键的元素 |
| ToLookUp | 经由过程建立一个一对多的字典，来组合元素。 |
GroupBy用法举例：
var countries = from r in Formulal.Racers
group r by r.Country into g
orderby g.Count() descending, g.Key
where g.Count() > 2
select new
{
Country = g.Key,
Count = g.Count()
};//猎取冠军次数大于2的国度
效果：
| Country | Count |
|---|---|
| UK | 10 |
| Brazil | 3 |
| Finland | 3 |
假如分组须要依据多个字段，则应当如许写：
//按组合键分组后，每组元素个数大于2的分组，按降序排序
var rtnByVal1 = from item in dataSource
group item by new { item.Val1, item.Val2 }
into g
where g.Count()>1
orderby g.Count() descending
select g; //按Val1和Val2组合为字典键，元素个数为值
var dict = rtnByVal1.ToDictionary(g=>g.First(),g=>g.Count());
6量词操作符
假如元素序列满足指定的前提 ,量词操作符就返回布尔值
| 组合运算符 | 形貌 |
|---|---|
| Any | 肯定鸠合中是不是有满足谓词函数的元素 |
| All | 肯定鸠合中是不是都满足谓词函数的元素 |
| Contains | 搜检某个元素是不是存在鸠合中 |
List<int> intList1 = new List<int>(5) {1, 2, 3, 4, 5};
bool any3 = intList1.Any(r => r == 3);//肯定鸠合中是不是有3，返回true
bool any0 = intList1.Any(r => r == 0);//肯定鸠合中是不是有0，返回false
bool allMoreZero = intList1.All(r => r > 0);//肯定序列中一切元素都满足大于0，返回true
bool allMore2 = intList1.All(r => r > 2); //返回false
bool contains3 = intList1.Contains(3); //元素3是不是在鸠合中，true
7分区操作符
分区操作符，返回一个子集。运用它们能够获得部份效果。
| 分区运算符 | 形貌 |
|---|---|
| Take | 必需制订提取元素的个数 |
| Skip | 跳过指定的元素个数，提取其他元素 |
| TakeWhile | 提取前提为真的元素 |
| SkipWhile | 跳过前提为真的元素 |
int pageSize = 5;
int numberPages = (int)Math.Ceiling(Formulal.Racers.Count() / (double)pageSize);
for (int page = 0; page < numberPages; page++)
{ var racersPartition =
(from r in Formulal.Racers
orderby r.LastName, r.FirstName
select r.FirstName + " " + r.LastName).Skip(page * pageSize).Take(pageSize);
}
效果：
Page 0Fernando Alons Mario Andretti Alberto Ascari Jack Brabham Jenson ButtonPage 1Jim Clark Juan Manuel Fa Nino Farina Emerson Fittipaldi Mika Hakkinen Page 2Lewis Hamilton Mike Hawthorn Damon Hill Graham Hill Phil Hill
8鸠合操作符（Set operators）
鸠合操作符返回 一 个鸠合。除了Distinct以外，其他都须要2个鸠合。
| 鸠合操作符 | 形貌 |
|---|---|
| Distinct | 从鸠合中删除反复的元素 |
| Union | 返回出现在个中一个鸠合中的唯一元素 |
| Intersect | 交集 |
| Except | 只出现在一个鸠合中的元素 |
| Zip | 经由过程运用指定的谓词函数兼并2个鸠合 |
运用举例：
List<int> intList1 = new List<int>(5) {1, 2, 3, 4, 5,3};
List<int> intList2 = new List<int>(3) {2, 5, 0};
var delDuplic = intList1.Distinct(); //去重，效果{1,2,3,4,5}
var unionList = intList1.Union(intList2); //并集,效果{1,2,3,4,5,0}
var interList = intList1.Intersect(intList2); //交集，效果{2,5}
var exceptList = intList1.Except(intList2);//差集，效果{1,3,4}
var exceptList2 = intList2.Except(intList1);//差集，效果{0}
var unionList2 = intList1.Zip(intList2,((i1, i2) => i1+", "+i2)); 效果：{{1,2}{2,5}{3,0}}
9元素操作符（Element operators）
这些元素操作符仅返回一 个元素。
| 元素操作符 | 形貌 |
|---|---|
| First | 返回第一个满足前提的元素 |
| FirstOrDefault | 返回第一个满足前提的元素，但假如没有找到满足前提的元素,就返回范例的默许值 |
| Last | 返回末了一个满足前提的元素 |
| LastOrDefault | 返回末了一个满足前提的元素，但假如没有找到满足前提的元素,就返回范例的默许值 |
| ElementAt | 指定了要返回的元素的位置 |
| ElementAtOrDefault | 指定了要返回的元素的位置，但假如没有找到满足前提的元素,就返回范例的默许值 |
| Single | 只返回一个满足前提的元素，假如有多个满足前提，就抛出一个非常。 |
| SingleOrDefault | 只返回一个满足前提的元素，但假如没有找到满足前提的元素,就返回范例的默许值 |
运用举例：
List<int> intList1 = new List<int>(5) { 1, 8, 3, 4, 5, 3 };
int firstMore1 = intList1.First(r => r > 1);//效果：8
int firstMore17 = intList1.FirstOrDefault(r => r > 17); //效果：0（由于不存在）
int lastMore3 = intList1.Last(r => r > 3); //效果5
int last = intList1.ElementAt(2); //效果3,（索引从0最先）
10聚合操作符（Aggregate operators）
聚合操作符盘算鸠合的一个值。应用这些聚合操作符 ,可 以盘算一切值的总和、一切元
素的个数、值最大和最小的元素 ,以 及平均值等
| 聚合操作符 | 形貌 |
|---|---|
| Count | 一切值的个数 |
| Sum | 一切值的综合 |
| Min | 一切值的的最小值 |
| Max | 一切值的的最大值 |
| Average | 一切值的平均数 |
public class MyIntClass
{
public string Name { get; set; }
public int Integar { get; set; }
public MyIntClass(string name, int i)
{
this.Name = name;
this.Integar = Integar;
}
}
List<MyIntClass> intList1 = new List<MyIntClass>(5)
{
new MyIntClass("first",1),
new MyIntClass("second",8) ,
new MyIntClass("third",3) ,
new MyIntClass("fourth",4) ,
new MyIntClass("fifth",5) ,
new MyIntClass("sixth",3)
};
int count = intList1.Count;
int sum = intList1.Sum(r=>r.Integar);
int min = intList1.Min(r => r.Integar);
int max = intList1.Max(r => r.Integar);
double average = intList1.Average(r => r.Integar);
11转换操作符（Conversion operators）
转换操作符将鸠合转换为数组 :IEnumberable、 IList, IDictionary 等。
| Conversion operators | 形貌 |
|---|---|
| ToArray | 鸠合转化为Array |
| AsEnumerable | 返回范例为IEnumerable< T> |
| ToList | 鸠合转化为List |
| ToDictionary | 鸠合转化为Dictionary |
| Cast< TResult> | 映照 |
照样上面的例子
IEnumerable<MyIntClass> ienuList = from r in intList1 where r.Integar > 3 select r; //返回默许的IEnumerable鸠合
List<MyIntClass> ienuList2 = (from r in intList1 where r.Integar > 3 select r).ToList(); //返回List
MyIntClass[] ienuList2 = (from r in intList1 where r.Integar > 3 select r).ToArray();//返回数组
var dict = (from r in intList1 where r.Integar > 3 select r).ToDictionary(r=>r.Name,r=>r.Integar);
//字典，key是name, value：Integar
IEnumerable<MyIntClass> ienuList2 = (from r in intList1 where r.Integar > 3 select r).AsEnumerable();
12生成操作符（Generation operators）
这些生成操作符返回 一 个新鸠合
| Generation operators | 形貌 |
|---|---|
| Empty | 鸠合是空的 |
| Range | 返回一系列数字 |
| Repeat | 返回一直反复一个值的鸠合 |
IEnumerable<int> ints = Enumerable.Range(3, 10);
//{3,4,5,6,7,8,9,10,11,12}IEnumerable<int> emptyInts = Enumerable.Empty<int>();
//生成一个空鸠合IEnumerable<int> ints2= Enumerable.Repeat(6,8);//生成8个6的鸠合
附：展现所用到的实体类和数据
选手实体类
//选手实体类
public class Racer
{
public Racer(string firstName = null, string lastName = null,
string country = null, int starts = 0,int wins = 0, IEnumerable<int> years = null, IEnumerable<string> cars = null)
{
this.FirstName = firstName;
this.LastName = lastName;
this.Country = country;
this.Starts = starts;
this.Wins = wins;
var yearList = new List<int>();
if (years != null)
{
foreach (var year in years)
{
yearList.Add(year);
} this.Years = yearList.ToArray();
} if (cars != null)
{ var carList = new List<string>();
foreach (var car in cars)
{
carList.Add(car);
}
this.Cars = carList.ToArray();
} public string FirstName { get; set; }
public string LastName { get; set; } //博得竞赛的次数
public int Wins { get; set; } //所属国度
public string Country { get; set; } //最先做的岁数
public int Starts { get; set; } //车型数组
public string[] Cars { get; private set; } //博得冠军的年份
public int[] Years { get; private set; }
}
}
选手数据
//选手List
public static List<Racer> Racers = new List<Racer>(40)
{
new Racer("Nino", "Farina", "Italy", 33, 5, new int[] { 1950 }, new string[] { "Alfa Romeo" }), new Racer("Alberto", "Ascari", "Italy", 32, 10, new int[] { 1952, 1953 }, new string[] { "Ferrari" }), new Racer("Juan Manuel", "Fangio", "Argentina", 51, 24, new int[] { 1951, 1954, 1955, 1956, 1957 }, new string[] { "Alfa Romeo", "Maserati", "Mercedes", "Ferrari" }), new Racer("Mike", "Hawthorn", "UK", 45, 3, new int[] { 1958 }, new string[] { "Ferrari" }), new Racer("Phil", "Hill", "USA", 48, 3, new int[] { 1961 }, new string[] { "Ferrari" }), new Racer("John", "Surtees", "UK", 111, 6, new int[] { 1964 }, new string[] { "Ferrari" }), new Racer("Jim", "Clark", "UK", 72, 25, new int[] { 1963, 1965 }, new string[] { "Lotus" }), new Racer("Jack", "Brabham", "Australia", 125, 14, new int[] { 1959, 1960, 1966 }, new string[] { "Cooper", "Brabham" }), new Racer("Denny", "Hulme", "New Zealand", 112, 8, new int[] { 1967 }, new string[] { "Brabham" }), new Racer("Graham", "Hill", "UK", 176, 14, new int[] { 1962, 1968 }, new string[] { "BRM", "Lotus" }), new Racer("Jochen", "Rindt", "Austria", 60, 6, new int[] { 1970 }, new string[] { "Lotus" }), new Racer("Jackie", "Stewart", "UK", 99, 27, new int[] { 1969, 1971, 1973 }, new string[] { "Matra", "Tyrrell" }), new Racer("Emerson", "Fittipaldi", "Brazil", 143, 14, new int[] { 1972, 1974 }, new string[] { "Lotus", "McLaren" }), new Racer("James", "Hunt", "UK", 91, 10, new int[] { 1976 }, new string[] { "McLaren" }), new Racer("Mario", "Andretti", "USA", 128, 12, new int[] { 1978 }, new string[] { "Lotus" }), new Racer("Jody", "Scheckter", "South Africa", 112, 10, new int[] { 1979 }, new string[] { "Ferrari" }), new Racer("Alan", "Jones", "Australia", 115, 12, new int[] { 1980 }, new string[] { "Williams" }), new Racer("Keke", "Rosberg", "Finland", 114, 5, new int[] { 1982 }, new string[] { "Williams" }), new Racer("Niki", "Lauda", "Austria", 173, 25, new int[] { 1975, 1977, 1984 }, new string[] { "Ferrari", "McLaren" }), new Racer("Nelson", "Piquet", "Brazil", 204, 23, new int[] { 1981, 1983, 1987 }, new string[] { "Brabham", "Williams" }), new Racer("Ayrton", "Senna", "Brazil", 161, 41, new int[] { 1988, 1990, 1991 }, new string[] { "McLaren" }), new Racer("Nigel", "Mansell", "UK", 187, 31, new int[] { 1992 }, new string[] { "Williams" }), new Racer("Alain", "Prost", "France", 197, 51, new int[] { 1985, 1986, 1989, 1993 }, new string[] { "McLaren", "Williams" }), new Racer("Damon", "Hill", "UK", 114, 22, new int[] { 1996 }, new string[] { "Williams" }), new Racer("Jacques", "Villeneuve", "Canada", 165, 11, new int[] { 1997 }, new string[] { "Williams" }), new Racer("Mika", "Hakkinen", "Finland", 160, 20, new int[] { 1998, 1999 }, new string[] { "McLaren" }), new Racer("Michael", "Schumacher", "Germany", 287, 91, new int[] { 1994, 1995, 2000, 2001, 2002, 2003, 2004 }, new string[] { "Benetton", "Ferrari" }), new Racer("Fernando", "Alonso", "Spain", 252, 32, new int[] { 2005, 2006 }, new string[] { "Renault" }), new Racer("Kimi", "Räikkönen", "Finland", 230, 20, new int[] { 2007 }, new string[] { "Ferrari" }), new Racer("Lewis", "Hamilton", "UK", 166, 43, new int[] { 2008, 2014, 2015 }, new string[] { "McLaren", "Mercedes" }), new Racer("Jenson", "Button", "UK", 283, 15, new int[] { 2009 }, new string[] { "Brawn GP" }), new Racer("Sebastian", "Vettel", "Germany", 156, 42, new int[] { 2010, 2011, 2012, 2013 }, new string[] { "Red Bull Racing" })
};
团队实体类
[Serializable] public class Team
{ public Team(string name, params int[] years)
{ this.Name = name;
this.Years = years;
} public string Name { get; private set; }
public int[] Years { get; private set; }
}
团队数据
//冠军团队List
public static List<Team> ChampionTeams = new List<Team>()
{ new Team("Vanwall", 1958),
new Team("Cooper", 1959, 1960),
new Team("Ferrari", 1961, 1964, 1975, 1976, 1977, 1979, 1982, 1983, 1999, 2000, 2001, 2002, 2003, 2004, 2007,
2008),
new Team("BRM", 1962),
new Team("Lotus", 1963, 1965, 1968, 1970, 1972, 1973, 1978),
new Team("Brabham", 1966, 1967),
new Team("Matra", 1969),
new Team("Tyrrell", 1971),
new Team("McLaren", 1974, 1984, 1985, 1988, 1989, 1990, 1991, 1998),
new Team("Williams", 1980, 1981, 1986, 1987, 1992, 1993, 1994, 1996, 1997),
new Team("Benetton", 1995),
new Team("Renault", 2005, 2006),
new Team("Brawn GP", 2009),
new Team("Red Bull Racing", 2010, 2011, 2012, 2013),
new Team("Mercedes", 2014, 2015)
};
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