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

 

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 + "<br />";
                }
                result.InnerHtml += "<br />";


                // 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 + "<br />";
                }
                result.InnerHtml += "<br />";
        }

 

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 + "<br />";
                }
                result.InnerHtml += "<br />";


                // 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 + "<br />";
                }
                result.InnerHtml += "<br />";
        }

 

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 + "<br />";
                }
                result.InnerHtml += "<br />";


                // 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 + "<br />";
                }
                result.InnerHtml += "<br />";
        }

 

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：<br />";

                        foreach (string s in g.Member)
                        {
                                result.InnerHtml += "--" + s + "<br />";
                        }
                }
                result.InnerHtml += "<br />";


                // 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：<br />";

                        foreach (string s in g.Member)
                        {
                                result.InnerHtml += "--" + s + "<br />";
                        }
                }
                result.InnerHtml += "<br />";
        }

 

 

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 + "<br />";
                }
                result.InnerHtml += "<br />";


                // 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 + "<br />";
                }
                result.InnerHtml += "<br />";
        }

 

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)
                {
                        result.InnerHtml += g.CategoryName + "：" + g.ProductCount + "<br />";

                }
                result.InnerHtml += "<br />";


                // 与上面的GroupJoin查询操作符相对应的查询语法
                var products2 = from c in _ctx.Categories
                                                join p in _ctx.Products on c.CategoryID equals p.CategoryID into g
                                                select new { CategoryName = c.CategoryName, ProductCount = g.Count() };


                foreach (var g in products2)
                {
                        result.InnerHtml += g.CategoryName + "：" + g.ProductCount + "<br />";

                }
                result.InnerHtml += "<br />";
        }

 

运行结果
Beverages：12
Condiments：12
Confections：13
Dairy Products：10
Grains/Cereals：7
Meat/Poultry：6
Produce：5
Seafood：12