.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