语言集成查询之Linq 入门

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Collections;using System.Text.RegularExpressions;using System.Reflection;namespace CSharp3StudyNote{ /// <summary> /// Ling To Objects 示例类 /// <para>1、Linq查询操作在数据源，查询本身及查询执行中是一个强类型的</para> /// <para>2、查询中表达式中的类型必须与数据源中的元素的类型和foreach语句中迭代变量类型兼容</para> /// <para>3、此强类型保证在编译时捕获类型异常，以便可以在用户遇到这些错误之前更正它们。</para> /// <para>查询语法和方法语法</para> /// <para>1、通过使用C#3.0中引入的声明性查询语法，介绍Linq文档中的多数查询都被编写成查询表达式，但是 /// .NET公共语言运行库（CLR）本身并不具有查询语句的概念。因此，在编译时查询表达式会转换在CLR确实了解的内容：方法调用。 /// 这些方法被称为“标准查询运算符”，他们具有以下名称：Where，Select，GroyupBy，Join，Max，Average。 /// </para> /// <para>可以通过使用方法语法而非查询语法直接调用这些方法。</para> /// </summary> public class LinqToObjects { /// <summary> /// 查询一个单词在一段文字中出现的次数． /// </summary> public void repeat() { string text = @"Burj Dubai, whose opening has been delayed twice since construction"+ @" began in 2004, will mark another milestone for the deeply indebted emirate with"+ @" a penchant for seeking new records."; string searchWord = "will"; string [] source=text.Split(new char[]{' ','.',',','?',':'}); var matchQuery = from word in source where word.ToLowerInvariant() == searchWord.ToLowerInvariant() select word; int wordCount = matchQuery.Count(); Console.WriteLine(searchWord+"在text中出现了："+wordCount.ToString()+"次。"); } /// <summary> /// 调用扩展方法查询 /// </summary> public void charTest() { string longString = "ABCDEF9923-2389J-ABCD1"; IEnumerable<char> stringQuery = from number in longString where Char.IsDigit(number) select number; //Execute the query foreach (char o in stringQuery) Console.Write("longString字符串中包含以下：" + o + "数字;/n"); Console.WriteLine("共总：" + stringQuery.Count()+"个数。"); IEnumerable<char> sQuery = longString.TakeWhile(c => c != '-'); foreach (char c in sQuery) Console.WriteLine("-前的字符串"+c); } /// <summary> /// 应用查询表达式，查询文件目录 /// </summary> public void QueryWithRegEx() { string startFolder = @"C:/Program Files/Microsoft Visual Studio 9.0/";//指定目录 IEnumerable<System.IO.FileInfo> fileList = GetFiles(startFolder);//获取该目录上的所有文件 //定义一个正规表达式 System.Text.RegularExpressions.Regex searchTerm = new System.Text.RegularExpressions.Regex(@"Visual (Basic|C#|C/+/+|J#|Studio|SoureSafe)"); //定义查询。 //1、首先找到出扩展名是htm的文件。 //2、然后把是htm文件的全名读取出来。 //3、使用扩展范围变量方法，来调用正规表达式对htm文件的内容进行匹配， //4、如果存在符合条件的文件就查询出来 var QueryMachineFiles = from file in fileList where file.Extension == ".htm" let fileText = System.IO.File.ReadAllText(file.FullName) let matches = searchTerm.Matches(fileText) where searchTerm.Matches(fileText).Count > 0 select new { name = file.FullName, matches = from System.Text.RegularExpressions.Match macth in matches select macth.Value }; Console.WriteLine("所匹配的文件名和文件："); Console.WriteLine(searchTerm.ToString()); foreach (var v in QueryMachineFiles) { //string s = v.name.Substring(startFolder.Length - 1); Console.WriteLine(v.name.ToString()); foreach (var v2 in v.matches) { Console.WriteLine(" " + v2.ToString()); } } } /// <summary> /// 使用Linq语方法查的垃圾文件 /// </summary> public void QueryRubbish() { string startFolder = @"C:/"; Console.WriteLine("正在读取..."); TimeSpan ts1 = new TimeSpan(DateTime.Now.Ticks);//所有时间。 IEnumerable<System.IO.FileInfo> fileList = GetFiles(startFolder); var RubbishFile = from file in fileList where file.Extension == ".tmp" let fileName = file.FullName select fileName; foreach (var v in RubbishFile) Console.WriteLine(v.ToString()); TimeSpan ts2 = new TimeSpan(DateTime.Now.Ticks); TimeSpan tempTime = ts2.Subtract(ts1).Duration(); string timeSpan = tempTime.Hours.ToString() + "小时" + tempTime.Minutes.ToString() + "分钟" + tempTime.Seconds.ToString() + "秒"+tempTime.Milliseconds.ToString()+"毫秒"; Console.WriteLine("查询用时：" + timeSpan); } /// <summary> ///获取文件方法 /// </summary> /// <param name="path">目录路径</param> /// <returns>文件集合</returns> public IEnumerable<System.IO.FileInfo> GetFiles(string path) { if (!System.IO.Directory.Exists(path)) throw new System.IO.DirectoryNotFoundException(); string[] fileNames = null; List<System.IO.FileInfo> files = new List<System.IO.FileInfo>(); fileNames = System.IO.Directory.GetFiles(path, "*.*", System.IO.SearchOption.AllDirectories); foreach (string name in fileNames) files.Add(new System.IO.FileInfo(name)); //foreach (string name in System.IO.Directory.GetFiles(path, "*.*", System.IO.SearchOption.AllDirectories)) // files.Add(new System.IO.FileInfo(name)); return files; } /// <summary> /// Linq 和反射 /// <para>.NET Framework类库反射API可用于检查.NET程序集中的元数据,及创健位于该程序集中的类型,类型成员,参数等等集合</para> /// <para>因为这些集合支持泛型IEnumerable接口,所以可以使用Linq查询他们</para> /// </summary> public void reflectionDemo() { string file = @"C:/Program Files/Microsoft Silverlight/3.0.40818.0/System.Core.dll"; Assembly assembly = Assembly.LoadFrom(file); var pubTypeQuery = from type in assembly.GetTypes() where type.IsPublic from method in type.GetMethods() where method.ReturnType.IsArray == true || (method.ReturnType.GetInterface(typeof(System.Collections.Generic.IEnumerable<>).FullName) != null && method.ReturnType.FullName != "System.String") group method.ToString() by type.ToString(); foreach (var groupMethods in pubTypeQuery) { Console.WriteLine("Return type:" + groupMethods.Key.ToString()); foreach (var method in groupMethods) { Console.WriteLine(" " + method.ToString()); } } } /// <summary> /// LinqToArrayList Demo /// <para>在使用Linq查询非泛型IEunmerable集合（ArrayList）时，必须显式声明范围变量的类型及反映此集合中对象的特定类型</para> /// </summary> public void LinqToArrayList() { //数据源 ArrayList alist = new ArrayList(); alist.Add(new Student { LastName = "LiLei", Score = new List<int> { 98, 93, 95 } }); alist.Add(new Student { LastName = "Lucy", Score = new List<int> { 100, 90, 85 } }); alist.Add(new Student { LastName = "LiLei", Score = new List<int> { 80, 70, 90 } }); alist.Add(new Student { LastName = "LiLei", Score = new List<int> { 75, 60, 78 } }); alist.Add(new Student { LastName = "LiLei", Score = new List<int> { 100, 120, 120 } }); //定义查询语句 var query = from Student student in alist //此处的范围变量显示的指定的强类型 where student.Score[0] > 85 select student; Console.WriteLine("第一课成绩大于85的有："); foreach (Student stu in query) Console.WriteLine("Student Name:{0}----Score:{1}",stu.LastName,stu.Score[0]); } }}