.NET 3.5(5) - LINQ查询操作符之Select、Where、OrderBy、OrderByDescending

浏览数：25 / 时间：2015年06月09日

介绍
    ·Select - Select选择；延迟
    ·Where - Where查询；延迟
    ·OrderBy - 按指定表达式对集合正序排序；延迟
    ·OrderByDescending - 按指定表达式对集合倒序排序；延迟
    ·GroupBy - 分组；延迟
    ·Join - Join查询；延迟
    ·GroupJoin - 分组Join查询；延迟
    ·以上查询操作符所对应的查询语法

示例
Summary.aspx.cs

using System;

using System.Data;

using System.Configuration;

using System.Collections;

using System.Linq;

using System.Web;

using System.Web.Security;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Web.UI.WebControls.WebParts;

using System.Web.UI.HtmlControls;

using System.Xml.Linq;

using System.Collections.Generic;

using DAL;

public partial class LINQ_Summary : System.Web.UI.Page

{

NorthwindDataContext _ctx = new NorthwindDataContext();

string[] _ary = null;

protected void Page_Load(object sender, EventArgs e)

{

_ary = new string[] { "asp.net", "csharp", "xhtml", "css", "javascript",

"wcf", "wpf", "silverlight", "linq", "wf",

"sqlserver", "asp.net ajax", "ssis", "ssas", "ssrs" };

// Select - Select选择；延迟

Summary_Select();

// Where - Where查询；延迟

Summary_Where();

// OrderBy - 按指定表达式对集合正序排序；延迟

// OrderByDescending - 按指定表达式对集合倒序排序；延迟

Summary_OrderBy_OrderByDescending();

// GroupBy - 分组；延迟

Summary_GroupBy();

// Join - Join查询；延迟

Summary_Join();

// GroupJoin - 分组Join查询；延迟

Summary_GroupJoin();

}

Select - Select选择；延迟

/// <summary>

/// Select - Select选择；延迟

/// </summary>

void Summary_Select()

{

// 使用Select查询操作符

var categories = _ctx.Categories.Select(

c => new { CategoryName = "类别名称：" + c.CategoryName });

foreach (var c in categories)

{

result.InnerHtml += c.CategoryName + " ";

}

result.InnerHtml += " ";

// 与上面的Select查询操作符相对应的查询语法

var categories2 = from c in _ctx.Categories

select new { CategoryName = "类别名称：" + c.CategoryName };

foreach (var c in categories2)

{

result.InnerHtml += c.CategoryName + " ";

}

result.InnerHtml += " ";

}

运行结果
类别名称：Beverages
类别名称：Condiments
类别名称：Confections
类别名称：Dairy Products
类别名称：Grains/Cereals
类别名称：Meat/Poultry
类别名称：Produce
类别名称：Seafood

Where - Where查询；延迟

/// <summary>

/// Where - Where查询；延迟

/// </summary>

void Summary_Where()

{

// 使用Where查询操作符

var ary = _ary.Where(a => a.StartsWith("w") && a.EndsWith("f"));

foreach (string s in ary)

{

result.InnerHtml += s + " ";

}

result.InnerHtml += " ";

// 与上面的Where查询操作符相对应的查询语法

var ary2 = from a in _ary

where a.StartsWith("w") && a.EndsWith("f")

select a;

foreach (string s in ary2)

{

result.InnerHtml += s + " ";

}

result.InnerHtml += " ";

}

运行结果
wcf
wpf
wf

OrderBy - 按指定表达式对集合正序排序；延迟
OrderByDescending - 按指定表达式对集合倒序排序；延迟

/// <summary>

/// OrderBy - 按指定表达式对集合正序排序；延迟

/// OrderByDescending - 按指定表达式对集合倒序排序；延迟

/// </summary>

void Summary_OrderBy_OrderByDescending()

{

// 使用OrderBy查询操作符

var ary = (from a in _ary

select a).OrderBy(a => a.Length); // OrderByDescending与OrderBy用法相同

foreach (string s in ary)

{

result.InnerHtml += s + " ";

}

result.InnerHtml += " ";

// 与上面的OrderBy查询操作符相对应的查询语法

var ary2 = from a in _ary

orderby a.Length ascending // orderby xxx descending与orderby xxx ascending用法相同

select a;

foreach (string s in ary2)

{

result.InnerHtml += s + " ";

}

result.InnerHtml += " ";

}

运行结果
wf
css
wcf
wpf
linq
ssis
ssas
ssrs
xhtml
csharp
asp.net
sqlserver
javascript
silverlight
asp.net ajax

GroupBy - 分组；延迟

/// <summary>

/// GroupBy - 分组；延迟

/// </summary>

void Summary_GroupBy()

{

// 使用GroupBy查询操作符

var list = (from a in _ary

select a).GroupBy(a => a.Length).Select(

g => new { Group = g.Key, Member = g });

foreach (var g in list)

{

result.InnerHtml += g.Group + "个字符： ";

foreach (string s in g.Member)

{

result.InnerHtml += "--" + s + " ";

}

result.InnerHtml += " ";

// 与上面的GroupBy查询操作符相对应的查询语法

var list2 = from a in _ary

group a by a.Length into g

select new { Group = g.Key, Member = g };

foreach (var g in list2)

{

result.InnerHtml += g.Group + "个字符： ";

foreach (string s in g.Member)

{

result.InnerHtml += "--" + s + " ";

}

result.InnerHtml += " ";

}

运行结果
7个字符：
--asp.net
6个字符：
--csharp
5个字符：
--xhtml
3个字符：
--css
--wcf
--wpf
10个字符：
--javascript
11个字符：
--silverlight
4个字符：
--linq
--ssis
--ssas
--ssrs
2个字符：
--wf
9个字符：
--sqlserver
12个字符：
--asp.net ajax

Join - Join查询；延迟

/// <summary>

/// Join - Join查询；延迟

/// </summary>

void Summary_Join()

{

// 使用Join查询操作符

var products = _ctx.Products.Join(

_ctx.Categories,

p => p.CategoryID,

c => c.CategoryID,

(p, c) => new { c.CategoryName, p.ProductName }).Take(5);

foreach (var p in products)

{

result.InnerHtml += p.CategoryName + " - " + p.ProductName + " ";

}

result.InnerHtml += " ";

// 与上面的Join查询操作符相对应的查询语法

var products2 = (from p in _ctx.Products

join c in _ctx.Categories

on p.CategoryID equals c.CategoryID

select new { c.CategoryName, p.ProductName }).Take(5);

foreach (var p in products2)

{

result.InnerHtml += p.CategoryName + " - " + p.ProductName + " ";

}

result.InnerHtml += " ";

}

运行结果
Beverages - Chai
Beverages - Chang
Condiments - Aniseed Syrup
Condiments - Chef Anton‘s Cajun Seasoning
Condiments - Chef Anton‘s Gumbo Mix

GroupJoin - 分组Join查询；延迟

/// <summary>

/// GroupJoin - 分组Join查询；延迟

/// </summary>

void Summary_GroupJoin()

{

// 使用GroupJoin查询操作符

var products = _ctx.Categories.GroupJoin(

_ctx.Products,

c => c.CategoryID,

p => p.CategoryID,

(p, g) => new { p.CategoryName, ProductCount = g.Count() });

foreach (var g in products)