LinQ实战学习笔记(四) LINQ to Object, 常用查询操作符

这一篇介绍了下面的内容:

• 查询object数组
• 查询强类型数组
• 查询泛型字典
• 查询字符串
• SelectMany
• 索引
• Distinct操作符
• 排序
• 嵌套查询
• 分组
• 组连接
• 内连接
• 左外连接
• 交叉连接
• skip,take

详细请参看代码.

 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Data;
 using System.Drawing;
 using System.Linq;
 using System.Text;
 using System.Windows.Forms;

 namespace WindowsFormsApplication1
 {
     public partial class Form1 : Form
     {
         public Form1()
         {
             InitializeComponent();
         }

         private void Form1_Load(object sender, EventArgs e)
         {

         }

         private void button1_Click(object sender, EventArgs e)
         {
             //查询object数组
             Object[] array = { "String", , true, 'a' };
             var types = array
                 .Select(s => s.GetType().Name)
                 .OrderBy(s => s);
             ObjectDumper.Write(types);
         }

         private void button2_Click(object sender, EventArgs e)
         {
             //查询强类型数组
             Book[] books ={
                 new Book{Title="Linq in Action"},
                 new Book{Title="Linq for Fun"},
                 new Book{Title="Extreme LINQ"}
             };

             var titles =
                 books
                 .Where(s => s.Title.Contains("Action"))
                 .Select(s => s.Title);

             ObjectDumper.Write(titles);
         }

         private void button3_Click(object sender, EventArgs e)
         {
             //查询泛型字典
             var dic = new Dictionary<int, string>();
             dic.Add(, "zero");
             dic.Add(, "un");
             dic.Add(, "deux");
             dic.Add(, "trois");
             dic.Add(, "quatre");
             var list =
                 dic
                 .Where(s => s.Key %  == )
                 .Select(s => s.Value);

             ObjectDumper.Write(list);
         }

         private void button4_Click(object sender, EventArgs e)
         {
             //查询字符串, 字符串实现了IEnumerable<Char>接口
             var count = "Non-letter characters in this string: 6"
                 .Where(s => !Char.IsLetter(s))
                 .Count();

             ObjectDumper.Write(count);
         }

         private void button5_Click(object sender, EventArgs e)
         {
             string[] books ={"Funny Stories","All your base are belong to us",
                                "LINQ rules","C# on Rails","Bonjour mon Amour"};
             var query =
                 books
                     .Where(s => s.Length > )
                     .Select(s => new { Book = s.ToUpper() });

             var query1 =
                 from s in books
                 where s.Length >
                 orderby s
                 select new { Book = s.ToUpper() };

             dataGridView1.DataSource = query1.ToList();
         }

         private void button6_Click(object sender, EventArgs e)
         {
             var query =
                 from s in SampleData.Books
                 where s.Title.Length >
                 orderby s.Title
                 select new { Book = s.Title, Price = s.Price };

             dataGridView2.DataSource = query.ToList();
         }

         private void button7_Click(object sender, EventArgs e)
         {
             //SelectMany

             var query1 =
                 SampleData.Books
                 .SelectMany(s => s.Authors);
             ObjectDumper.Write(query1);

             var query =
                 from book in SampleData.Books
                 from author in book.Authors
                 select author.FirstName + author.LastName;

             ObjectDumper.Write(query);
         }

         private void button8_Click(object sender, EventArgs e)
         {
             var book =
                 SampleData.Books
                     .Select((s, no) => new { no, s.Title })
                     .OrderBy(s => s.Title);

             //无法翻译为等同的查询表达式语法

             ObjectDumper.Write(book);

         }

         private void button9_Click(object sender, EventArgs e)
         {
             //Distinct操作符
             var query =
                 SampleData.Books
                     .SelectMany(s => s.Authors)
                     .Select(s => s.FirstName + s.LastName);
             ObjectDumper.Write(query);

             //去除重复的author,C#没有和distinct等同的查询表达式
             var query1 =
                 SampleData.Books
                     .SelectMany(s => s.Authors)
                     .Distinct()
                     .Select(s => s.FirstName + s.LastName);
             Console.WriteLine();
             ObjectDumper.Write(query1);

         }

         private void button10_Click(object sender, EventArgs e)
         {
             //排序
             var query =
                 from s in SampleData.Books
                 orderby s.Publisher.Name, s.Price descending, s.Title
                 select new
                 {
                     Publisher=s.Publisher.Name,
                     s.Price,
                     s.Title
                 };
             dataGridView1.DataSource = query.ToList();
             ObjectDumper.Write(query);

             var query1 =
                 SampleData.Books
                 .OrderBy(s => s.Publisher.Name)
                 .ThenByDescending(s => s.Price)
                 .ThenBy(s => s.Title)
                 .Select(s => new
                     {
                         publisher = s.Publisher.Name,
                         s.Price,
                         s.Title
                     });
             Console.WriteLine();
             ObjectDumper.Write(query1);

         }

         private void button11_Click(object sender, EventArgs e)
         {
             //嵌套查询

             var query =
                 from s in SampleData.Publishers
                 select new
                 {
                     item1 = s.Name,
                     item2 =
                         from book in SampleData.Books
                         where book.Publisher.Name == s.Name
                         select book
                 };

             foreach (var m in query)
             {
                 Console.WriteLine(m.item1+":");
                 foreach (var k in m.item2)
                 {
                     Console.WriteLine(k.Title);
                 }
                 Console.WriteLine();
             }

         }

         private void button12_Click(object sender, EventArgs e)
         {
             //分组
             //代码让图书按出版社分组.属于同一出版社的图书将被分到相同的组中.
             //在这个查询中,该分组publisherBooks对象是IGrouping<TKey,T>接口.
             //其中T为集合IEnumerable<Book>

             var query =
                 from s in SampleData.Books
                 group s by s.Publisher into publisherBooks
                 select new
                 {
                     publisher=publisherBooks.Key.Name,
                     books=publisherBooks,
                     booksum=publisherBooks.Count()
                 };
             foreach (var m in query)
             {
                 Console.WriteLine(m.publisher + ":");
                 foreach (var k in m.books)
                 {
                     Console.WriteLine(k.Title);
                 }
                 Console.WriteLine(m.booksum);
                 Console.WriteLine();
             }

         }

         private void button13_Click(object sender, EventArgs e)
         {
             //组连接
             var query =
                 from s in SampleData.Publishers
                 join book in SampleData.Books
                 on s equals book.Publisher into publisherBooks
                 select new
                 {
                     publisher=s.Name,
                     books=publisherBooks
                 };

             foreach (var m in query)
             {
                 Console.WriteLine(m.publisher + ":");
                 foreach (var k in m.books)
                 {
                     Console.WriteLine(k.Title);
                 }
                 Console.WriteLine();
             }

         }

         private void button14_Click(object sender, EventArgs e)
         {
             //内连接,旨在找到两个序列的交集
             //和组连接的差别是,没有使用into关键字将元素分组,而是将图书投影在了出版社对象上
             //注意没有任何书籍的出版社没有显示出来,这是因为在两个待连接序列中均符合条件的组合才会出现在结果序列中.
             var query =
                 from s in SampleData.Publishers
                 join book in SampleData.Books on s equals book.Publisher
                 select new
                 {
                     publisher=s.Name,
                     books=book.Title
                 };

             var query2=
                 SampleData.Publishers
                     .Join(SampleData.Books,     //内部序列
                         s=>s,                   //外部的key选择器
                         book=>book.Publisher,   //内部的key选择器
                         (s,book)=>new           //结果选择器
                         {
                             publisher=s.Name,
                             books=book.Title
                         });

             ObjectDumper.Write(query2);

             foreach (var m in query)
             {
                 Console.WriteLine(m.publisher + ":");
                 Console.WriteLine(m.books);
                 Console.WriteLine();
             }

         }

         private void button15_Click(object sender, EventArgs e)
         {
             //左外连接
             var query =
                 from s in SampleData.Publishers
                 join book in SampleData.Books
                     on s equals book.Publisher into publisherBooks
                 from book in publisherBooks.DefaultIfEmpty()            //为空序列提供默认元素
                 select new
                 {
                     publisher=s.Name,
                     books=book==default(Book)?"(no books)":book.Title
                 };

             ObjectDumper.Write(query);
         }

         private void button16_Click(object sender, EventArgs e)
         {
             //交叉连接, 计算出两个序列中所有元素的积
             //结果序列由一个序列的每个元素和另一个序列中每个元素的完全组合构成
             var query =
                 from s in SampleData.Publishers
                 from book in SampleData.Books
                 select new
                 {
                     correct=(s==book.Publisher),
                     publisher=s.Name,
                     books=book.Title
                 };
             ObjectDumper.Write(query);
         }

         private void button17_Click(object sender, EventArgs e)
         {
             //skip,take
             var list1 = new List<string>();
             for (int i = ; i < ; i++)
                 list1.Add(i.ToString());

             var query =
                 list1
                 .Select(s=>s)
                 .Skip().Take();

             ObjectDumper.Write(query);
         }

     }

 }

本节源代码下载

原创文章,出自"博客园, 猪悟能'S博客" : http://www.cnblogs.com/hackpig/