Language set query Ganmge hteg.ratedQuw, LINQ, integrates the query syntax in the C# programming language, and can use the same Syntax for accessing different data sources. LINQ provides an abstraction layer for different data sources, so the same syntax can be used.
Filter operator defines the conditions for returning elements.
Filter operator | Description |
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Use predicates to return a Boolean value | |
Filter elements based on type |
where Usage:
var racers = from r in Formulal.Racers where r.Wins > 15 && r.Country == "Brazil" select r;
Projection OperatorDescription
##select | |
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select usage | selectMany usagevar 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 Copy after login | 3 Sorting operator
Sort operator
Ascending order | |
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ThenBy | |
ThenByDescending | |
Reverse | |
4 connection | Operator
Joins can be joined based on key selector functions 2 collections | |
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##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 Copy after login | Result: |
Yearj |
Racerj=Michael Schumacher | Teamj =Ferrari | |
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Teamj =Renault | Yearj=2006 | |
Teamj =Renault | ##Yearj= 2007 | |
Teamj =Ferrari | Yearj=2008 | |
Teamj =Ferrari | Yearj=2014 | |
Teamj =Mercedes | Yearj=2015 | |
Teamj =Mercedes | ##Yearj=2009 | Racerj=Jenson Button |
##Yearj=2010 | Racerj=Sebastian Vettel | |
Yearj=2011 | Racerj=Sebastian Vettel | |
Yearj=2012 | Racerj=Sebastian Vettel | |
Yearj=2013 | Racerj=Sebastian Vettel | |
5 Combination Operator | Put data in groups | |
Combining Operator | Description |
ToLookUp | combines elements by creating a one-to-many dictionary. |
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//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 }; Copy after login | Result: |
Count |
UK
10
3 | |
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needs to be based on multiple fields | , it should be written like this: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 Copy after login | 6
If the element sequence meets the specified conditions, the quantifier operator returns a Boolean value |
Determine whether all elements in the set satisfy the predicate function | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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分区运算符 | 描述 |
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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); }
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
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 |
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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}}
这些元素操作符仅返回一 个元素。
元素操作符 | 描述 |
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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)
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 |
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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);
转换操作符将集合转换为数组 :IEnumberable、 IList, IDictionary 等。
Conversion operators | 描述 |
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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();
这些生成操作符返回 一 个新集合
Generation operators | 描述 |
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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
//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; } } }
//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" }) };
[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; } }
//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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