无涯教程：C#与VB.NET的LINQ离线学习PDF

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无涯教程(LearnFk)的《LinQ教程离线版.pdf》是一份专注于.NET Framework中的 LINQ (Language Integrated Query) 技术的教学资料。LINQ 是微软为C#和Visual Basic .NET编程语言引入的一项创新，旨在将SQL风格的查询语言无缝融入到这两种.NET语言中，使得开发者无需深入了解底层数据库查询语法，也能方便地操作各种数据源，如对象集合、数据库、XML文档等。该教程的核心理念是利用一种自然的查询语法，允许程序员以类似SQL的方式编写查询，例如筛选、排序、分组和聚合等操作。在C#和VB.NET中，通过`System.Linq`命名空间提供的类库和方法，如`from`、`where`、`select`等关键字，可以实现对对象列表的操作，如上述代码所示。举个例子，C#代码展示了如何从一个字符串数组中获取长度小于或等于5的单词。`from word in words where word.Length <= 5 select word`这一行，通过LINQ表达式的形式，筛选出符合条件的元素并返回。然后，遍历这些短单词并打印出来，输出结果是"hello", "LINQ", 和 "world"。在VB.NET版本中，代码结构相似，通过`From`到`Select`的语法块实现了相同的功能。这个例子体现了LINQ的强大之处，它不仅适用于简单的数据过滤，还可以用于更复杂的查询场景，如连接多个数据源、进行异步操作或者在LINQ to SQL和LINQ to XML等不同上下文中执行查询。《无涯教程-LINQ教程离线版》提供了深入理解和应用LINQ的基础知识，帮助.NET开发者提升数据处理效率和代码的可读性。无论是初学者还是进阶者，都能从中获益匪浅，学会如何优雅地操作各种数据结构，提高开发生产力。

using System;

using System.Collections.Generic;

using System.Linq;

namespace Operators {

class JoinTables {

class DepartmentClass {

public int DepartmentId { get; set; }

public string Name { get; set; }

}

class EmployeeClass {

public int EmployeeId { get; set; }

public string EmployeeName { get; set; }

public int DepartmentId { get; set; }

}

static void Main(string[] args) {

List <DepartmentClass> departments = new List <DepartmentClass>();

departments.Add(new DepartmentClass { DepartmentId = 1, Name = "Account" });

departments.Add(new DepartmentClass { DepartmentId = 2, Name = "Sales" });

departments.Add(new DepartmentClass { DepartmentId = 3, Name = "Marketing" });

List <EmployeeClass> employees = new List <EmployeeClass>();

employees.Add(new EmployeeClass { DepartmentId = 1, EmployeeId = 1, EmployeeName = "William" });

employees.Add(new EmployeeClass { DepartmentId = 2, EmployeeId = 2, EmployeeName = "Miley" });

employees.Add(new EmployeeClass { DepartmentId = 1, EmployeeId = 3, EmployeeName = "Benjamin" });

var list = (from e in employees join d in departments on e.DepartmentId equals d.DepartmentId

select new {

EmployeeName = e.EmployeeName,

DepartmentName = d.Name

});

foreach (var e in list) {

Console.WriteLine("Employee Name={0} , Department Name={1}", e.EmployeeName, e.DepartmentName);

}

Console.WriteLine("\nPress any key to continue.");

Console.ReadKey();

}

Module Module1

Sub Main()

Dim account As New Department With {.Name = "Account", .DepartmentId = 1}

Dim sales As New Department With {.Name = "Sales", .DepartmentId = 2}

Dim marketing As New Department With {.Name = "Marketing", .DepartmentId = 3}

Dim departments As New System.Collections.Generic.List(Of Department)(New Department() {account,

sales, marketing})

Dim william As New Employee With {.EmployeeName = "William", .EmployeeId = 1, .DepartmentId = 1}

Dim miley As New Employee With {.EmployeeName = "Miley", .EmployeeId = 2, .DepartmentId = 2}

Dim benjamin As New Employee With {.EmployeeName = "Benjamin", .EmployeeId = 3, .DepartmentId = 1}

Dim employees As New System.Collections.Generic.List(Of Employee)(New Employee() {william, miley,

benjamin})

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