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步步为营VS 2008 + .NET 3.5(5) - LINQ查询操作符之Select、Where、OrderBy、OrderByDescending、GroupBy、Join、GroupJoin及其对应的查询语法
作者:
webabcd
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
OK
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