基本概念

LINQ（Language Integrated Query）?：LINQ(Language Integrated Query)語言集成查詢是一組用于c#和Visual Basic語言的擴展。它允許編寫C#或者Visual Basic代碼以操作內存數據的方式，查詢數據庫。

問題描述

已有Racer類和冠軍車手數據，進行以下查詢，并打印結果：

1）查詢來自英國（UK）的所有世界冠軍，并按勝利場數降序排列。

輸出結果時，可用Console.WriteLine("{0:A}",?racer)或WriteLine($"{racer:A}");。

2）使用LINQ方法語法重寫這個查詢。

3）體會LINQ的推遲查詢：首先建立查詢query2，查出所有勝利場數超過25，用foreach循環并打印；然后將所有英國（UK）車手的國名改為“United?Kingdom”；再次對query2用foreach循環并打印。觀賽同一查詢的不同執行結果。

4）查出首發場數超過100，并且勝利場數超過20的車手的姓名（包含名和姓）。

5）基于現有數據，統計德國人的勝利總場數。

6）進行投影查詢，對于駕馭法拉利（Ferrari）車型奪冠的車手，輸出人名、國別與首發勝率，人名包含名和姓，首發勝率為Wins除以Starts。?

源代碼?

using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks;namespace Homework8 {public class Racer : IComparable<Racer>, IFormattable{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 yearsList = new List<int>();foreach (var year in years){yearsList.Add(year);}this.Years = yearsList.ToArray();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; }public string Country { get; set; }public int Wins { get; set; }//奪冠場數public int Starts { get; set; }//首發場數public string[] Cars { get; private set; }//賽車手獲得冠軍那一年使用的所有車型public int[] Years { get; private set; }//賽車手獲得冠軍的年份public override string ToString(){return String.Format("{0} {1}", FirstName, LastName);}public int CompareTo(Racer other){if (other == null) throw new ArgumentNullException("other");return this.LastName.CompareTo(other.LastName);}public string ToString(string format){return ToString(format, null);}public string ToString(string format,IFormatProvider formatProvider){switch (format){case null:case "N":return ToString();case "F":return FirstName;case "L":return LastName;case "C":return Country;case "S":return Starts.ToString();case "W":return Wins.ToString();case "A":return String.Format("{0} {1}, {2}; starts: {3}, wins: {4}",FirstName, LastName, Country, Starts, Wins);default:throw new FormatException(String.Format("Format {0} not supported", format));}}public static IList<Racer> GetChampions()//1950-2008年一級方程式錦標賽冠軍{IList<Racer> racers = new List<Racer>(40);racers.Add(new Racer("Nino", "Farina", "Italy", 33, 5, new int[] { 1950 }, new string[] { "Alfa Romeo" }));racers.Add(new Racer("Alberto", "Ascari", "Italy", 32, 10, new int[] { 1952, 1953 }, new string[] { "Ferrari" }));racers.Add(new Racer("Juan Manuel", "Fangio", "Argentina", 51, 24, new int[] { 1951, 1954, 1955, 1956, 1957 }, new string[] { "Alfa Romeo", "Maserati", "Mercedes", "Ferrari" }));racers.Add(new Racer("Mike", "Hawthorn", "UK", 45, 3, new int[] { 1958 }, new string[] { "Ferrari" }));racers.Add(new Racer("Phil", "Hill", "USA", 48, 3, new int[] { 1961 }, new string[] { "Ferrari" }));racers.Add(new Racer("John", "Surtees", "UK", 111, 6, new int[] { 1964 }, new string[] { "Ferrari" }));racers.Add(new Racer("Jim", "Clark", "UK", 72, 25, new int[] { 1963, 1965 }, new string[] { "Lotus" }));racers.Add(new Racer("Jack", "Brabham", "Australia", 125, 14, new int[] { 1959, 1960, 1966 }, new string[] { "Cooper", "Brabham" }));racers.Add(new Racer("Denny", "Hulme", "New Zealand", 112, 8, new int[] { 1967 }, new string[] { "Brabham" }));racers.Add(new Racer("Graham", "Hill", "UK", 176, 14, new int[] { 1962, 1968 }, new string[] { "BRM", "Lotus" }));racers.Add(new Racer("Jochen", "Rindt", "Austria", 60, 6, new int[] { 1970 }, new string[] { "Lotus" }));racers.Add(new Racer("Jackie", "Stewart", "UK", 99, 27, new int[] { 1969, 1971, 1973 }, new string[] { "Matra", "Tyrrell" }));racers.Add(new Racer("Emerson", "Fittipaldi", "Brazil", 143, 14, new int[] { 1972, 1974 }, new string[] { "Lotus", "McLaren" }));racers.Add(new Racer("James", "Hunt", "UK", 91, 10, new int[] { 1976 }, new string[] { "McLaren" }));racers.Add(new Racer("Mario", "Andretti", "USA", 128, 12, new int[] { 1978 }, new string[] { "Lotus" }));racers.Add(new Racer("Jody", "Scheckter", "South Africa", 112, 10, new int[] { 1979 }, new string[] { "Ferrari" }));racers.Add(new Racer("Alan", "Jones", "Australia", 115, 12, new int[] { 1980 }, new string[] { "Williams" }));racers.Add(new Racer("Keke", "Rosberg", "Finland", 114, 5, new int[] { 1982 }, new string[] { "Williams" }));racers.Add(new Racer("Niki", "Lauda", "Austria", 173, 25, new int[] { 1975, 1977, 1984 }, new string[] { "Ferrari", "McLaren" }));racers.Add(new Racer("Nelson", "Piquet", "Brazil", 204, 23, new int[] { 1981, 1983, 1987 }, new string[] { "Brabham", "Williams" }));racers.Add(new Racer("Ayrton", "Senna", "Brazil", 161, 41, new int[] { 1988, 1990, 1991 }, new string[] { "McLaren" }));racers.Add(new Racer("Nigel", "Mansell", "UK", 187, 31, new int[] { 1992 }, new string[] { "Williams" }));racers.Add(new Racer("Alain", "Prost", "France", 197, 51, new int[] { 1985, 1986, 1989, 1993 }, new string[] { "McLaren", "Williams" }));racers.Add(new Racer("Damon", "Hill", "UK", 114, 22, new int[] { 1996 }, new string[] { "Williams" }));racers.Add(new Racer("Jacques", "Villeneuve", "Canada", 165, 11, new int[] { 1997 }, new string[] { "Williams" }));racers.Add(new Racer("Mika", "Hakkinen", "Finland", 160, 20, new int[] { 1998, 1999 }, new string[] { "McLaren" }));racers.Add(new Racer("Michael", "Schumacher", "Germany", 250, 91, new int[] { 1994, 1995, 2000, 2001, 2002, 2003, 2004 }, new string[] { "Benetton", "Ferrari" }));racers.Add(new Racer("Fernando", "Alonso", "Spain", 132, 21, new int[] { 2005, 2006 }, new string[] { "Renault" }));racers.Add(new Racer("Kimi", "R?ikk?nen", "Finland", 148, 17, new int[] { 2007 }, new string[] { "Ferrari" }));racers.Add(new Racer("Lewis", "Hamilton", "UK", 44, 9, new int[] { 2008 }, new string[] { "McLaren" }));return racers;}}/*利用LINQ技術查詢Racer對象已有Racer類和冠軍車手數據，進行以下查詢，并打印結果：1）查詢來自英國（UK）的所有世界冠軍，并按勝利場數降序排列。輸出結果時，可用Console.WriteLine("{0:A}", racer)或WriteLine($"{racer:A}");。2）使用LINQ方法語法重寫這個查詢。3）體會LINQ的推遲查詢：首先建立查詢query2，查出所有勝利場數超過25，用foreach循環并打印；然后將所有英國（UK）車手的國名改為“United Kingdom”；再次對query2用foreach循環并打印。觀賽同一查詢的不同執行結果。4）查出首發場數超過100，并且勝利場數超過20的車手的姓名（包含名和姓）。5）基于現有數據，統計德國人的勝利總場數。6）進行投影查詢，對于駕馭法拉利（Ferrari）車型奪冠的車手，輸出人名、國別與首發勝率，人名包含名和姓，首發勝率為Wins除以Starts。 */class Program{static void Main(string[] args){Console.WriteLine("1）查詢來自英國（UK）的所有世界冠軍，并按勝利場數降序排列。");List<Racer> list = new List<Racer>(Racer.GetChampions());list.Sort((a,b) => {return b.Wins - a.Wins;});foreach (var racer in list){if(racer.Country == "UK")Console.WriteLine("{0:A}", racer);}Console.WriteLine("2）使用LINQ方法語法重寫這個查詢。");var query1 = from r in Racer.GetChampions()where r.Country == "UK"orderby r.Wins descendingselect r;foreach (var racer in query1){Console.WriteLine("{0:A}", racer);}Console.WriteLine("3）體會LINQ的推遲查詢：首先建立查詢query2，查出所有勝利場數超過25，用foreach循環并打印；然后將所有英國（UK）車手的國名改為“United Kingdom”；再次對query2用foreach循環并打印。觀賽同一查詢的不同執行結果。");var query2 = from r in Racer.GetChampions()where r.Wins > 25orderby r.Wins descendingselect r;foreach (var racer in query2){Console.WriteLine("{0:A}", racer);if (racer.Country == "UK")racer.Country = "United Kingdom";}foreach (var racer in query2){Console.WriteLine("{0:A}", racer);}Console.WriteLine("4）查出首發場數超過100，并且勝利場數超過20的車手的姓名（包含名和姓）。");var query3 = from r in Racer.GetChampions()where r.Starts >100 where r.Wins > 20orderby r.Wins descendingselect r.FirstName + " " + r.LastName;foreach (var racer in query3){Console.WriteLine("{0:A}", racer);}Console.WriteLine("5）基于現有數據，統計德國人的勝利總場數。");var query4 = from r in Racer.GetChampions()where r.Country == "Germany"orderby r.Wins descendingselect r.Wins;Console.WriteLine(query4.Sum());Console.WriteLine("6）進行投影查詢，對于駕馭法拉利（Ferrari）車型奪冠的車手，輸出人名、國別與首發勝率，人名包含名和姓，首發勝率為Wins除以Starts。");var query5 = from r in Racer.GetChampions()from c in r.Carswhere c == "Ferrari"orderby r.Wins descendingselect new { name = r.FirstName + " " + r.LastName , Country=r.Country, rate=(double)r.Wins/r.Starts };foreach (var racer in query5){Console.WriteLine("{0:A}", racer);}}} }

運行結果

參考文章

https://www.pianshen.com/article/159246876/

https://www.cnblogs.com/hackpig/archive/2010/02/15/1668448.html

https://www.cnblogs.com/chquwa/p/3792901.html

https://blog.csdn.net/liujunjie612/article/details/46639417

與50位技術專家面對面20年技術見證，附贈技術全景圖

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