HOW TO：查詢物件集合 (C# 程式設計手冊)
這個範例顯示如何針對 Student 物件清單執行簡單查詢。每個 Student 物件都包含一些學生的基本資訊，以及一份代表學生四次考試分數的清單。
這個應用程式是本節中其他使用相同 students 資料來源的許多範例的架構。
範例
下列查詢會傳回第一次考試分數高於 90 分的學生。
public class StudentClass
{
#region data
protected enum GradeLevel { FirstYear = 1, SecondYear, ThirdYear, FourthYear };
protected class Student
{
public string FirstName { get; set; }
public string LastName { get; set; }
public int ID { get; set; }
public GradeLevel Year;
public List<int> ExamScores;
}
protected static List<Student> students = new List<Student>
{
new Student {FirstName = "Terry", LastName = "Adams", ID = 120,
Year = GradeLevel.SecondYear,
ExamScores = new List<int>{ 99, 82, 81, 79}},
new Student {FirstName = "Fadi", LastName = "Fakhouri", ID = 116,
Year = GradeLevel.ThirdYear,
ExamScores = new List<int>{ 99, 86, 90, 94}},
new Student {FirstName = "Hanying", LastName = "Feng", ID = 117,
Year = GradeLevel.FirstYear,
ExamScores = new List<int>{ 93, 92, 80, 87}},
new Student {FirstName = "Cesar", LastName = "Garcia", ID = 114,
Year = GradeLevel.FourthYear,
ExamScores = new List<int>{ 97, 89, 85, 82}},
new Student {FirstName = "Debra", LastName = "Garcia", ID = 115,
Year = GradeLevel.ThirdYear,
ExamScores = new List<int>{ 35, 72, 91, 70}},
new Student {FirstName = "Hugo", LastName = "Garcia", ID = 118,
Year = GradeLevel.SecondYear,
ExamScores = new List<int>{ 92, 90, 83, 78}},
new Student {FirstName = "Sven", LastName = "Mortensen", ID = 113,
Year = GradeLevel.FirstYear,
ExamScores = new List<int>{ 88, 94, 65, 91}},
new Student {FirstName = "Claire", LastName = "O'Donnell", ID = 112,
Year = GradeLevel.FourthYear,
ExamScores = new List<int>{ 75, 84, 91, 39}},
new Student {FirstName = "Svetlana", LastName = "Omelchenko", ID = 111,
Year = GradeLevel.SecondYear,
ExamScores = new List<int>{ 97, 92, 81, 60}},
new Student {FirstName = "Lance", LastName = "Tucker", ID = 119,
Year = GradeLevel.ThirdYear,
ExamScores = new List<int>{ 68, 79, 88, 92}},
new Student {FirstName = "Michael", LastName = "Tucker", ID = 122,
Year = GradeLevel.FirstYear,
ExamScores = new List<int>{ 94, 92, 91, 91}},
new Student {FirstName = "Eugene", LastName = "Zabokritski", ID = 121,
Year = GradeLevel.FourthYear,
ExamScores = new List<int>{ 96, 85, 91, 60}}
};
#endregion
//Helper method, used in GroupByRange.
protected static int GetPercentile(Student s)
{
double avg = s.ExamScores.Average();
return avg > 0 ? (int)avg / 10 : 0;
}
public void QueryHighScores(int exam, int score)
{
var highScores = from student in students
where student.ExamScores[exam] > score
select new {Name = student.FirstName, Score = student.ExamScores[exam]};
foreach (var item in highScores)
{
Console.WriteLine("{0,-15}{1}", item.Name, item.Score);
}
}
}
public class Program
{
public static void Main()
{
StudentClass sc = new StudentClass();
sc.QueryHighScores(1, 90);
// Keep the console window open in debug mode.
Console.WriteLine("Press any key to exit");
Console.ReadKey();
}
}
這個查詢故意設計的如此簡單，好讓您可以自行學習。例如，您可以在 where 子句中嘗試其他述詞 (Predicate)，或使用 orderby 子句來排序結果。
編譯程式碼
建立以 .NET Framework 3.5 版為目標的 Visual Studio 專案。根據預設，專案有 System.Core.dll 的參考，以及 System.Linq 命名空間的 using 指示詞。
將程式碼複製至您的專案中。
按 F5 編譯和執行程式。
按任何鍵離開主控台視窗。