Linq StandardQueryOperator
Language Set Query Ganmge hteg.ratedQuw, LINQ, integriert die Abfragesyntax in die Programmiersprache C# und kann dieselbe Syntax verwenden für den Zugriff auf verschiedene Datenquellen. LINQ stellt eine Abstraktionsschicht für verschiedene Datenquellen bereit, sodass dieselbe Syntax verwendet werden kann.
1 Filteroperator
Der Filteroperator definiert die Bedingungen für die Rückgabe von Elementen.
| 筛选操作符 |
描述 |
| where |
使用谓词，返回布尔值 |
| OfType< TResult> |
根据类型筛选元素 |
Anwendungsbeispiele:
wobei Verwendung:
var racers = from r in Formulal.Racers
where r.Wins > 15 && r.Country == "Brazil" select r;
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OfType2-Projektionsoperator
object[] data = {"one", 2, "three", 4, 5, "six"};
var rtnData = data.OfType<string>(); //返回类型为string的数据元素集合Nach dem Login kopieren
Konvertieren Sie
Objekt
in ein neues Objekt eines anderen Typs
| Projektionsoperator | Beschreibung< /th> |
|---|
| select | |
| selectMany | |
Verwendungsbeispiele:
Verwendung auswählen
AuswahlMany-Verwendung
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共计3个属性的对象集合Nach dem Login kopieren
3 Sortieroperator
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);//筛选出驾驶法拉利的选手集合Nach dem Login kopieren
ändert die Reihenfolge der zurückgegebenen Elemente
Beispiel:
| 排序操作符 | 描述 |
|---|
| OrderBy | 升序排序 |
| OrderByDescending | 降序排序 |
| ThenBy | 第一次排序结果类似，用第二次升序排序 |
| ThenByDescending | 第一次排序结果类似，用第二次降序排序 |
| Reverse | 反转集合中元素的顺序 |
4 Verkettung
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
};//国家为巴西，按照胜场次数降序排列Nach dem Login kopieren
Operator
Wird zum Zusammenführen von Mengen verwendet, die nicht direkt miteinander verbunden sind
| 连接运算符 | 描述 |
|---|
| Join | 可以根据键选择器函数连接连接2个集合 |
| GroupJoin | 连接两个集合,组合其结果 |
Ergebnis:
//Join连接
//获取冠军年份在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)
}; //获取冠军年份在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)
}; //连接
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
};Nach dem Login kopieren
5 Kombinationsoperatoren
| 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 |
Daten in Gruppen zusammenfassen
GroupBy-Verwendungsbeispiel:
| 组合运算符 | 描述 |
|---|
| GroupBy | 组合有公共键的元素 |
| ToLookUp | 通过创建一个一对多的字典，来组合元素。 |
Ergebnis:
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()
};//获取冠军次数大于2的国家Nach dem Login kopieren
| Country | Count |
|---|
| UK | 10 |
| Brazil | 3 |
| Finland | 3 |
Wenn
Gruppe auf mehreren Feldern basieren muss, es sollte wie folgt geschrieben werden:
6
//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());Nach dem Login kopieren
Quantifizierer
OperatorWenn die Elementsequenz die angegebenen Bedingungen erfüllt, gibt der Quantifiziereroperator einen booleschen Wert zurück
| Kompositionsoperator | Beschreibung |
|---|
| Beliebig< /td> | Bestimmen Sie, ob es Elemente in der Menge gibt, die die Prädikatfunktion erfüllen |
| Alle | Bestimmen Sie, ob alle Elemente in der Menge die Prädikatfunktion erfüllen |
| Enthält | Überprüfen Sie, ob ein Element in der Sammlung vorhanden ist |
List<int> intList1 = new List<int>(5) {1, 2, 3, 4, 5};
bool any3 = intList1.Any(r => r == 3);//确定集合中是否有3，返回true
bool any0 = intList1.Any(r => r == 0);//确定集合中是否有0，返回false
bool allMoreZero = intList1.All(r => r > 0);//确定序列中所有元素都满足大于0，返回true
bool allMore2 = intList1.All(r => r > 2); //返回false
bool contains3 = intList1.Contains(3); //元素3是否在集合中，trueNach dem Login kopieren
7分区操作符
分区操作符，返回一个子集。使用它们可以得到部分结果。
| 分区运算符 | 描述 |
|---|
| Take | 必须制定提取元素的个数 |
| Skip | 跳过指定的元素个数，提取其他元素 |
| TakeWhile | 提取条件为真的元素 |
| SkipWhile | 跳过条件为真的元素 |
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);
}Nach dem Login kopieren
结果：
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
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8集合操作符（Set operators）
集合操作符返回 一 个集合。除了Distinct之外，其他都需要2个集合。
| 集合操作符 | 描述 |
|---|
| Distinct | 从集合中删除重复的元素 |
| Union | 返回出现在其中一个集合中的唯一元素 |
| Intersect | 交集 |
| Except | 只出现在一个集合中的元素 |
| Zip | 通过使用指定的谓词函数合并2个集合 |
应用举例：
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，结果{1,2,3,4,5}
var unionList = intList1.Union(intList2); //并集,结果{1,2,3,4,5,0}
var interList = intList1.Intersect(intList2); //交集，结果{2,5}
var exceptList = intList1.Except(intList2);//差集，结果{1,3,4}
var exceptList2 = intList2.Except(intList1);//差集，结果{0}
var unionList2 = intList1.Zip(intList2,((i1, i2) => i1+", "+i2)); 结果：{{1,2}{2,5}{3,0}}Nach dem Login kopieren
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 | 描述 |
|---|
| First | 返回第一个满足条件的元素 |
| FirstOrDefault | 返回第一个满足条件的元素，但如果没有找到满足条件的元素,就返回类型的默认值 |
| Last | 返回最后一个满足条件的元素 |
| LastOrDefault | 返回最后一个满足条件的元素，但如果没有找到满足条件的元素,就返回类型的默认值 |
| 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，但如果没有找到满足条件的元素,就返回类型的默认值 |
| Single | 只返回一个满足条件的元素，如果有多个满足条件，就抛出一个异常。 |
| SingleOrDefault | 只返回一个满足条件的元素，但如果没有找到满足条件的元素,就返回类型的默认值 |
应用举例：
List<int> intList1 = new List<int>(5) { 1, 8, 3, 4, 5, 3 };
int firstMore1 = intList1.First(r => r > 1);//结果：8
int firstMore17 = intList1.FirstOrDefault(r => r > 17); //结果：0（因为不存在）
int lastMore3 = intList1.Last(r => r > 3); //结果5
int last = intList1.ElementAt(2); //结果3,（索引从0开始）Nach dem Login kopieren
10聚合操作符（Aggregate operators）
聚合操作符计算集合的一个值。利用这些聚合操作符 ,可 以计算所有值的总和、所有元
素的个数、值最大和最小的元素 ,以 及平均值等
| 聚合操作符 | 描述 |
|---|
| Count | 所有值的个数 |
| Sum | 所有值的综合 |
| Min | 所有值的的最小值 |
| Max | 所有值的的最大值 |
| Average | 所有值的平均数 |
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);Nach dem Login kopieren
11转换操作符（Conversion operators）
转换操作符将集合转换为数组 :IEnumberable、 IList, IDictionary 等。
| Conversion operators | 描述 |
|---|
| ToArray | 集合转化为Array |
| AsEnumerable | 返回类型为IEnumerable< T> |
| ToList | 集合转化为List |
| ToDictionary | 集合转化为Dictionary |
| Cast< TResult> | 映射 |
还是上面的例子
IEnumerable<MyIntClass> ienuList = from r in intList1 where r.Integar > 3 select r; //返回默认的IEnumerable集合
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();Nach dem Login kopieren
12生成操作符（Generation operators）
这些生成操作符返回 一 个新集合
| Generation operators | 描述 |
|---|
| Empty | 集合是空的 |
| Range | 返回一系列数字 |
| Repeat | 返回始终重复一个值的集合 |
IEnumerable<int> ints = Enumerable.Range(3, 10);
//{3,4,5,6,7,8,9,10,11,12}IEnumerable<int> emptyInts = Enumerable.Empty<int>();
//生成一个空集合IEnumerable<int> ints2= Enumerable.Repeat(6,8);//生成8个6的集合Nach dem Login kopieren
附：展示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; } //赢得比赛的次数
public int Wins { get; set; } //所属国家
public string Country { get; set; } //开始做的年龄
public int Starts { get; set; } //车型数组
public string[] Cars { get; private set; } //赢得冠军的年份
public int[] Years { get; private set; }
}
}Nach dem Login kopieren
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" })
};Nach dem Login kopieren
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; }
}Nach dem Login kopieren
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)
};Nach dem Login kopieren
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