C#语法中的select
第一次学着用Linq的盆友们，可以看看哈。。。。
代码 Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->class SelectSample1 { static void Main() { //Create the data source List<int> Scores = new List<int>() { 97, 92, 81, 60 }; // Create the query. IEnumerable<int> queryHighScores = from score in Scores where score > 80 select score; // Execute the query. foreach (int i in queryHighScores) { Console.Write(i + " "); } } }
2、集合序列化：
private XElement SerializeDesignerItems(IEnumerable<DesignerItem> designerItems) { XElement serializedItems = new XElement("DesignerItems", from item in designerItems let contentXaml = XamlWriter.Save(((DesignerItem)item).Content) select new XElement("DesignerItem", new XElement("Left", Canvas.GetLeft(item)), new XElement("Top", Canvas.GetTop(item)), new XElement("Width", item.Width), new XElement("Height", item.Height), new XElement("ID", item.ID), new XElement("zIndex", Canvas.GetZIndex(item)), new XElement("IsGroup", item.IsGroup), new XElement("ParentID", item.ParentID), new XElement("Content", contentXaml) ) ); return serializedItems; }
下面的示例演示了 select 子句可能采用的所有不同形式。在每个查询中，请注意 select 子句和查询变量（studentQuery1、studentQuery2 等）的类型之间的关系。
class SelectSample2 { // Define some classes public class Student { public string First { get; set; } public string Last { get; set; } public int ID { get; set; } public List<int> Scores; public ContactInfo GetContactInfo(SelectSample2 app, int id) { ContactInfo cInfo = (from ci in app.contactList where ci.ID == id select ci) .FirstOrDefault(); return cInfo; } public override string ToString() { return First + " " + Last + ":" + ID; } } public class ContactInfo { public int ID { get; set; } public string Email { get; set; } public string Phone { get; set; } public override string ToString() { return Email + "," + Phone; } } public class ScoreInfo { public double Average { get; set; } public int ID { get; set; } } // The primary data source List<Student> students = new List<Student>() { new Student {First="Svetlana", Last="Omelchenko", ID=111, Scores= new List<int>() {97, 92, 81, 60}}, new Student {First="Claire", Last="O'Donnell", ID=112, Scores= new List<int>() {75, 84, 91, 39}}, new Student {First="Sven", Last="Mortensen", ID=113, Scores= new List<int>() {88, 94, 65, 91}}, new Student {First="Cesar", Last="Garcia", ID=114, Scores= new List<int>() {97, 89, 85, 82}}, }; // Separate data source for contact info. List<ContactInfo> contactList = new List<ContactInfo>() { new ContactInfo {ID=111, Email="SvetlanO@Contoso.com", Phone="206-555-0108"}, new ContactInfo {ID=112, Email="ClaireO@Contoso.com", Phone="206-555-0298"}, new ContactInfo {ID=113, Email="SvenMort@Contoso.com", Phone="206-555-1130"}, new ContactInfo {ID=114, Email="CesarGar@Contoso.com", Phone="206-555-0521"} }; static void Main(string[] args) { SelectSample2 app = new SelectSample2(); // Produce a filtered sequence of unmodified Students. IEnumerable<Student> studentQuery1 = from student in app.students where student.ID > 111 select student; Console.WriteLine("Query1: select range_variable"); foreach (Student s in studentQuery1) { Console.WriteLine(s.ToString()); } // Produce a filtered sequence of elements that contain // only one property of each Student. IEnumerable<String> studentQuery2 = from student in app.students where student.ID > 111 select student.Last; Console.WriteLine("\r\n studentQuery2: select range_variable.Property"); foreach (string s in studentQuery2) { Console.WriteLine(s); } // Produce a filtered sequence of objects created by // a method call on each Student. IEnumerable<ContactInfo> studentQuery3 = from student in app.students where student.ID > 111 select student.GetContactInfo(app, student.ID); Console.WriteLine("\r\n studentQuery3: select range_variable.Method"); foreach (ContactInfo ci in studentQuery3) { Console.WriteLine(ci.ToString()); } // Produce a filtered sequence of ints from // the internal array inside each Student. IEnumerable<int> studentQuery4 = from student in app.students where student.ID > 111 select student.Scores[0]; Console.WriteLine("\r\n studentQuery4: select range_variable[index]"); foreach (int i in studentQuery4) { Console.WriteLine("First score = {0}", i); } // Produce a filtered sequence of doubles // that are the result of an expression. IEnumerable<double> studentQuery5 = from student in app.students where student.ID > 111 select student.Scores[0] * 1.1; Console.WriteLine("\r\n studentQuery5: select expression"); foreach (double d in studentQuery5) { Console.WriteLine("Adjusted first score = {0}", d); } // Produce a filtered sequence of doubles that are // the result of a method call. IEnumerable<double> studentQuery6 = from student in app.students where student.ID > 111 select student.Scores.Average(); Console.WriteLine("\r\n studentQuery6: select expression2"); foreach (double d in studentQuery6) { Console.WriteLine("Average = {0}", d); } // Produce a filtered sequence of anonymous types // that contain only two properties from each Student. var studentQuery7 = from student in app.students where student.ID > 111 select new { student.First, student.Last }; Console.WriteLine("\r\n studentQuery7: select new anonymous type"); foreach (var item in studentQuery7) { Console.WriteLine("{0}, {1}", item.Last, item.First); } // Produce a filtered sequence of named objects that contain // a method return value and a property from each Student. // Use named types if you need to pass the query variable // across a method boundary. IEnumerable<ScoreInfo> studentQuery8 = from student in app.students where student.ID > 111 select new ScoreInfo { Average = student.Scores.Average(), ID = student.ID }; Console.WriteLine("\r\n studentQuery8: select new named type"); foreach (ScoreInfo si in studentQuery8) { Console.WriteLine("ID = {0}, Average = {1}", si.ID, si.Average); } // Produce a filtered sequence of students who appear on a contact list // and whose average is greater than 85. IEnumerable<ContactInfo> studentQuery9 = from student in app.students where student.Scores.Average() > 85 join ci in app.contactList on student.ID equals ci.ID select ci; Console.WriteLine("\r\n studentQuery9: select result of join clause"); foreach (ContactInfo ci in studentQuery9) { Console.WriteLine("ID = {0}, Email = {1}", ci.ID, ci.Email); } // Keep the console window open in debug mode Console.WriteLine("Press any key to exit."); Console.ReadKey(); } } /* Output Query1: select range_variable Claire O'Donnell:112 Sven Mortensen:113 Cesar Garcia:114 studentQuery2: select range_variable.Property O'Donnell Mortensen Garcia studentQuery3: select range_variable.Method ClaireO@Contoso.com,206-555-0298 SvenMort@Contoso.com,206-555-1130 CesarGar@Contoso.com,206-555-0521 studentQuery4: select range_variable[index] First score = 75 First score = 88 First score = 97 studentQuery5: select expression Adjusted first score = 82.5 Adjusted first score = 96.8 Adjusted first score = 106.7 studentQuery6: select expression2 Average = 72.25 Average = 84.5 Average = 88.25 studentQuery7: select new anonymous type O'Donnell, Claire Mortensen, Sven Garcia, Cesar studentQuery8: select new named type ID = 112, Average = 72.25 ID = 113, Average = 84.5 ID = 114, Average = 88.25 studentQuery9: select result of join clause ID = 114, Email = CesarGar@Contoso.com */
