C# LINQ标准查询操作符

内容导读

互联网集市收集整理的这篇技术教程文章主要介绍了C# LINQ标准查询操作符，小编现在分享给大家，供广大互联网技能从业者学习和参考。文章包含9144字，纯文字阅读大概需要14分钟。

内容图文

首先添加数据集合

                 1
                [Serializable]

                 2
                public
                class Racer : IComparable<Racer>, IFormattable
 3    {
 4public Racer()
 5        { }
 6public Racer(string firstName, string lastName, string country, int starts, int wins)
 7           : this(firstName, lastName, country, starts, wins, null, null)
 8        {
 9        }
10public Racer(string firstName, string lastName, string country, int starts, int wins, IEnumerable<int> years, IEnumerable<string> cars)
11        {
12this.FirstName = firstName;
13this.LastName = lastName;
14this.Country = country;
15this.Starts = starts;
16this.Wins = wins;
17this.Years = new List<int>(years);
18this.Cars = new List<string>(cars);
19        }
20publicstring FirstName { get; set; }
21publicstring LastName { get; set; }
22publicstring Country { get; set; }
23publicint Wins { get; set; }
24publicint Starts { get; set; }
25public IEnumerable<string> Cars { get; privateset; }
26public IEnumerable<int> Years { get; privateset; }
2728publicoverridestring ToString()
29        {
30return String.Format("{0} {1}", FirstName, LastName);
31        }
3233publicint CompareTo(Racer other)
34        {
35if (other == null) return -1;
36returnstring.Compare(this.LastName, other.LastName);
37        }
3839publicstring ToString(string format)
40        {
41return ToString(format, null);
42        }
4344publicstring ToString(string format,
45              IFormatProvider formatProvider)
46        {
47switch (format)
48            {
49casenull:
50case"N":
51return ToString();
52case"F":
53return FirstName;
54case"L":
55return LastName;
56case"C":
57return Country;
58case"S":
59return Starts.ToString();
60case"W":
61return Wins.ToString();
62case"A":
63return String.Format("{0} {1}, {2}; starts: {3}, wins: {4}",
64                          FirstName, LastName, Country, Starts, Wins);
65default:
66thrownew FormatException(String.Format("Format {0} not supported", format));
67            }
68        }
69     }

View Code

                 1
                private
                static List<Racer> racers;
 2 3publicstatic IList<Racer> GetChampions()
 4    {
 5if (racers == null)
 6      {
 7         racers = new List<Racer>(40);
 8         racers.Add(new Racer("Nino", "Farina", "Italy", 33, 5, newint[] { 1950 }, newstring[] { "Alfa Romeo" }));
 9         racers.Add(new Racer("Alberto", "Ascari", "Italy", 32, 10, newint[] { 1952, 1953 }, newstring[] { "Ferrari" }));
10         racers.Add(new Racer("Juan Manuel", "Fangio", "Argentina", 51, 24, newint[] { 1951, 1954, 1955, 1956, 1957 }, newstring[] { "Alfa Romeo", "Maserati", "Mercedes", "Ferrari" }));
11         racers.Add(new Racer("Mike", "Hawthorn", "UK", 45, 3, newint[] { 1958 }, newstring[] { "Ferrari" }));
12         racers.Add(new Racer("Phil", "Hill", "USA", 48, 3, newint[] { 1961 }, newstring[] { "Ferrari" }));
13         racers.Add(new Racer("John", "Surtees", "UK", 111, 6, newint[] { 1964 }, newstring[] { "Ferrari" }));
14         racers.Add(new Racer("Jim", "Clark", "UK", 72, 25, newint[] { 1963, 1965 }, newstring[] { "Lotus" }));
15         racers.Add(new Racer("Jack", "Brabham", "Australia", 125, 14, newint[] { 1959, 1960, 1966 }, newstring[] { "Cooper", "Brabham" }));
16         racers.Add(new Racer("Denny", "Hulme", "New Zealand", 112, 8, newint[] { 1967 }, newstring[] { "Brabham" }));
17         racers.Add(new Racer("Graham", "Hill", "UK", 176, 14, newint[] { 1962, 1968 }, newstring[] { "BRM", "Lotus" }));
18         racers.Add(new Racer("Jochen", "Rindt", "Austria", 60, 6, newint[] { 1970 }, newstring[] { "Lotus" }));
19         racers.Add(new Racer("Jackie", "Stewart", "UK", 99, 27, newint[] { 1969, 1971, 1973 }, newstring[] { "Matra", "Tyrrell" }));
20         racers.Add(new Racer("Emerson", "Fittipaldi", "Brazil", 143, 14, newint[] { 1972, 1974 }, newstring[] { "Lotus", "McLaren" }));
21         racers.Add(new Racer("James", "Hunt", "UK", 91, 10, newint[] { 1976 }, newstring[] { "McLaren" }));
22         racers.Add(new Racer("Mario", "Andretti", "USA", 128, 12, newint[] { 1978 }, newstring[] { "Lotus" }));
23         racers.Add(new Racer("Jody", "Scheckter", "South Africa", 112, 10, newint[] { 1979 }, newstring[] { "Ferrari" }));
24         racers.Add(new Racer("Alan", "Jones", "Australia", 115, 12, newint[] { 1980 }, newstring[] { "Williams" }));
25         racers.Add(new Racer("Keke", "Rosberg", "Finland", 114, 5, newint[] { 1982 }, newstring[] { "Williams" }));
26         racers.Add(new Racer("Niki", "Lauda", "Austria", 173, 25, newint[] { 1975, 1977, 1984 }, newstring[] { "Ferrari", "McLaren" }));
27         racers.Add(new Racer("Nelson", "Piquet", "Brazil", 204, 23, newint[] { 1981, 1983, 1987 }, newstring[] { "Brabham", "Williams" }));
28         racers.Add(new Racer("Ayrton", "Senna", "Brazil", 161, 41, newint[] { 1988, 1990, 1991 }, newstring[] { "McLaren" }));
29         racers.Add(new Racer("Nigel", "Mansell", "UK", 187, 31, newint[] { 1992 }, newstring[] { "Williams" }));
30         racers.Add(new Racer("Alain", "Prost", "France", 197, 51, newint[] { 1985, 1986, 1989, 1993 }, newstring[] { "McLaren", "Williams" }));
31         racers.Add(new Racer("Damon", "Hill", "UK", 114, 22, newint[] { 1996 }, newstring[] { "Williams" }));
32         racers.Add(new Racer("Jacques", "Villeneuve", "Canada", 165, 11, newint[] { 1997 }, newstring[] { "Williams" }));
33         racers.Add(new Racer("Mika", "Hakkinen", "Finland", 160, 20, newint[] { 1998, 1999 }, newstring[] { "McLaren" }));
34         racers.Add(new Racer("Michael", "Schumacher", "Germany", 287, 91, newint[] { 1994, 1995, 2000, 2001, 2002, 2003, 2004 }, newstring[] { "Benetton", "Ferrari" }));
35         racers.Add(new Racer("Fernando", "Alonso", "Spain", 177, 27, newint[] { 2005, 2006 }, newstring[] { "Renault" }));
36         racers.Add(new Racer("Kimi", "R?ikk?nen", "Finland", 148, 17, newint[] { 2007 }, newstring[] { "Ferrari" }));
37         racers.Add(new Racer("Lewis", "Hamilton", "UK", 90, 17, newint[] { 2008 }, newstring[] { "McLaren" }));
38         racers.Add(new Racer("Jenson", "Button", "UK", 208, 12, newint[] { 2009 }, newstring[] { "Brawn GP" }));
39         racers.Add(new Racer("Sebastian", "Vettel", "Germany", 81, 21, newint[] { 2010, 2011 }, newstring[] { "Red Bull Racing" }));
40      }
4142return racers;
43     }

View Code

1、where子句

            1
            var racers = from r in Formula1.GetChampions()
2where r.Wins > 15 && (r.Country == "Brazil" || r.Country == "Austria")
3select r;
4var item = Formula1.GetChampions().Where(p => p.Wins > 15 && (p.Country == "Brazil" || p.Country == "Austria")).Select(r => r);

2、根据索引筛选

            1
            var racers = Formula1.GetChampions().
2                     Where((r, index) => r.LastName.StartsWith("A") && index % 2 != 0);

3、类型筛选

            1
            object[] data = { "one", 2, 3, "four", "five", 6 };
2var query = data.OfType<string>();

4、复合的from子句

            1
            var ferrariDrivers = from r in Formula1.GetChampions()
2from c in r.Cars
3where c == "Ferrari"4orderby r.LastName
5select r.FirstName + "" + r.LastName;
6var item = Formula1.GetChampions().SelectMany(r => r.Cars, (r, c) => new { Racer = r, Car = c }).
7                      Where(r => r.Car == "Ferrari").OrderBy(r => r.Racer.LastName).Select(r => r.Racer.FirstName + "" + r.Racer.LastName);

5、排序

            1
            var racers = from r in Formula1.GetChampions()
2where r.Country == "Brazil"3orderby r.Wins descending
4select r;
5var racers2= from r in Formula1.GetChampions()
6orderby r.Country,r.LastName,r.FirstName
7select r;
8var racers3 = Formula1.GetChampions().OrderBy(r => r.Country).ThenBy(r => r.LastName).ThenBy(r => r.FirstName);

6、分组

             1
             2
            var countries = from r in Formula1.GetChampions()
 3                            group r by r.Country into g
 4orderby g.Count() descending, g.Key
 5where g.Count() >= 2 6selectnew { Country = g.Key, Count = g.Count() };
 7 8var item = Formula1.GetChampions().GroupBy(r => r.Country).OrderByDescending(p => p.Count()).
 9                     ThenBy(p => p.Key).Where(p => p.Count() >= 2).Select(p => new { Country = p.Key, Count = p.Count() });
10

7、内链接

             1
            var racers = from r in Formula1.GetChampions()
 2from y in r.Years
 3selectnew 4                         {
 5                              Year = y,
 6                              Name = r.FirstName + "" + r.LastName
 7                         };
 8 9var teams = from t in Formula1.GetContructorChampions()
10from y in t.Years
11selectnew12                        {
13                             Year = y,
14                             Name = t.Name
15                        };

8、左连接

             1
            var racersAndTeams =
 2               (from r in racers
 3                join t in teams on r.Year equals t.Year into rt
 4from t in rt.DefaultIfEmpty()
 5orderby r.Year
 6selectnew 7               {
 8                    Year = r.Year,
 9                    Champion = r.Name,
10                    Constructor = t == null ? "no constructor championship" : t.Name
11                }).Take(10);

9、zip 合并

             1
            var racerNames = from r in Formula1.GetChampions()
 2where r.Country == "Italy" 3orderby r.Wins descending
 4selectnew 5                             {
 6                                  Name = r.FirstName + "" + r.LastName
 7                             };
 8 9var racerNamesAndStarts = from r in Formula1.GetChampions()
10where r.Country == "Italy"11orderby r.Wins descending
12selectnew13                                      {
14                                           LastName = r.LastName,
15                                           Starts = r.Starts
16                                      };
171819var racers = racerNames.Zip(racerNamesAndStarts, (first, second) => first.Name + ", starts: " + second.Starts);

10、聚合函数

             1
            var query = from r in Formula1.GetChampions()
 2                         let numberYears = r.Years.Count()
 3 4where numberYears >= 3 5orderby numberYears descending, r.LastName
 6selectnew 7                        {
 8                             Name = r.FirstName + "" + r.LastName,
 9                             TimesChampion = numberYears
10                        };
1112var countries = (from c in13from r in Formula1.GetChampions()
14                                 group r by r.Country into c
15selectnew16                                 {
17                                      Country = c.Key,
18                                      Wins = (from r1 in c
19select r1.Wins).Sum()
20                                 }
21orderby c.Wins descending, c.Country
22select c).Take(5);

原文：http://www.cnblogs.com/farmer-y/p/5977483.html

内容总结

以上是互联网集市为您收集整理的C# LINQ标准查询操作符全部内容，希望文章能够帮你解决C# LINQ标准查询操作符所遇到的程序开发问题。如果觉得互联网集市技术教程内容还不错，欢迎将互联网集市网站推荐给程序员好友。

内容备注

版权声明：本文内容由互联网用户自发贡献，该文观点与技术仅代表作者本人。本站仅提供信息存储空间服务，不拥有所有权，不承担相关法律责任。如发现本站有涉嫌侵权/违法违规的内容，请发送邮件至 gblab@vip.qq.com 举报，一经查实，本站将立刻删除。

内容手机端

扫描二维码推送至手机访问。

本文链接：https://qyyshop.com/info/1085233.html

来源：【匿名】

【上一篇】C#特性之数据类型【下一篇】assemblyinfo.csC#Assembly类访问程序集信息

更多 ►

【C# LINQ标准查询操作符】教程文章相关的互联网学习教程文章

问题描述：原数据---------需要在原视图数据中，统计出每个Device_Num设备号下面的交易的总额和分别统计出微信支付宝的交易总额。解决：从上图数据没办法使用直接查询出要求的数据。 .1.首先查出满足需要的数据的类型，并进行分组SELECT SUM(Amount) as TotleAmount ,Trade_type ,Device_Num FROM patientbookstatices GROUP BY Device_Num ,Trade_type；得到数据:还是无法查出按要求的数据，2.我们以上图数据作...

C#程序中使用LINQ to XML来查询XML格式数据的实例

LINQ to XML 是一种启用了 LINQ 的内存 XML 编程接口，使用它，可以在 .NET Framework 编程语言中处理 XML。它将 XML 文档置于内存中，这一点很像文档对象模型 (DOM)。您可以查询和修改 XML 文档，修改之后，可以将其另存为文件，也可以将其序列化然后通过网络发送。但是，LINQ to XML 与 DOM 不同：它提供一种新的对象模型，这是一种更轻量的模型，使用也更方便，这种模型利用了 VisualC# 2008 在语言方面的改进。LINQ to XML ...

c# MongoDB分页辅助类，支持多条件查询【代码】

创建一个获取MongoDB数据库实例的类publicclass Db{privatestatic IMongoDatabase db = null;privatestaticreadonlyobject lockHelper = newobject();private Db() { }publicstatic IMongoDatabase GetDb(string connStr, string dbName){if (db == null){lock (lockHelper){if (db == null){var client = new MongoClient(connStr);db = client.GetDatabase(dbName);}}}return db;}}创建一个操作MongDB的辅助类publicclass MongoD...

C#实现按键弹出查询窗口

protected override bool ProcessCmdKey(ref Message msg, Keys keyData) { if (keyData == Keys.F2) { this.OnKeyPress(new KeyPressEventArgs(‘r‘)); return true; } else return base.ProcessCmdKey(ref msg, keyData); }原文：https://www.cnblogs.com/Evan-fanfan/p/9286464.html

C# LINQ查询表达式用法对应Lambda表达式【代码】【图】

C#编程语言非常优美，我个人还是非常赞同的。特别是在学习一段时间C#后发现确实在它的语法和美观度来说确实要比其它编程语言强一些（也可能是由于VS编译器的加持）用起来非常舒服，而且对于C#我觉得他最优美之处不仅仅是语法糖方面还有就是体现在LINQ和Lambda表达式。本篇文简单介绍一下关于C#当中LINQ表达式和其对应的Lambda表达式的用法，关于这两部分内容的相关参考资料：人民邮电出版社《C#程序设计及应用教程》（第3版）博客园...

C#实现航班查询及预订

using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Linq;using System.Text;using System.Threading.Tasks;using System.Windows.Forms;using System.Data.SqlClient;namespace FrmHangBanUser{ public partial class FrmUser : Form { //1.连接字符串 string connString = "Data Source = .;Initial Catalog=Ticket;User ID ...

c#读取快递100查询返回的JSON信息【代码】

{"message":"ok","nu":"1105016801203","companytype":"ems","ischeck":"1","com":"ems","updatetime":"2014-08-01 10:17:31","status":"200","condition":"F00","codenumber":"1105016801203","data":[{"time":"2014-07-30 16:47:00","location":"","context":"赤峰市邮政速递物流分公司新华路揽投部妥投本人收签收","ftime":"2014-07-30 16:47:00"},{"time":"2014-07-30 15:18:00","location":"","context":"赤峰市邮政速递物流...

C#快递单号查询源码

源码本人测试过，没有啥问题，能查询快递单号，支持的快递还挺多，圆通快递、申通快递、韵达快递的都支持单号查询的，程序是通过向爱快递(www.aikuaidi.cn)接口传输参数来查询快递单号，我直接把代码帖出来，很好的解决我单个开发的麻烦。?1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283848586878889909192939...

C# AD(Active Directory)域信息同步，组织单位、用户等信息查询【代码】【图】

示例准备打开上一篇文章配置好的AD域控制器开始菜单-->管理工具-->Active Directory 用户和计算机新建组织单位和用户　新建层次关系如下：知识了解　　我们要用C#访问Active Directory非常容易，主要用到轻量目录访问协议 (LDAP)System.DirectoryServices命名空间下的两个组件类DirectoryEntry和DirectorySeacher 读取AD域信息示例　示例在Framework 3.5下用Winform程序编写　主要结合常见需求读取组织单位(OU)及用户(User)...

c# 经验谈：巧用Expression表达式解决类似于sql中 select in 的查询【代码】【图】

我们在项目经常会碰到一些特殊需求例如下拉框是复选的，查询条件是根据下拉框中复选项进行拼接看到此图后大家肯定会说，这很简单嘛将所有的选项拼成“‘1-3‘,‘5-9‘” 然后放到 in 的字句后面，一查就出来了。这样做的确在逻辑上没有问题，可是大家有没有想过这个问题，过度的和业务耦合虽然能够解决现在的需求但是却牺牲了代码优雅和可维护性其实本文的目的是想利用Expression表达式在linq查询中实现一个优雅的解决方案，同...

c#程序中使用"like“查询access数据库查询为空的问题

今天，在开发的过程中发现了一个特别奇怪的问题：access中like查询时候，在Access数据库中执行，发现可以查询出结果，这是在数据库上执行，select * from KPProj where KpName like ‘*测试*‘，但是同样的语句在c#程序中却查询为空，这是什么情况呢？这个问题真让人纠结，通过以前的开发经验，access中like需要用*号，但是sqlserver oracle数据库中要用标准的%，为什么此时就不行呢？经过搜索资料，最后发现是连接access驱动程序的...

NHibernate3剖析：Query篇之NHibernate.Linq增强查询【代码】【图】

系列引入 NHibernate3.0剖析系列分别从Configuration篇、Mapping篇、Query篇、Session策略篇、应用篇等方面全面揭示NHibernate3.0新特性和应用及其各种应用程序的集成，基于NHibernte3.0版本。如果你还不熟悉NHibernate，可以快速阅读NHibernate之旅系列文章导航系列入门，如果你已经在用NHibernate了，那么请跟上NHibernate3.0剖析系列吧。NHibernate专题：http://kb.cnblogs.com/zt/nhibernate/NHibernate官方站点：http://nhfor...

C# 与 Oracle 中 BINARY_DOUBLE数据类型查询

Oracle 10g新增 BINARY_DOUBLE 数据类型，而.NET暂不支持这个类型，查询时需要转换为 NUMBER。 eg： "SELECT RAWTOHEX(OID) AS OID,RAWTOHEX(FLAVOROID) AS FLAVOROID,BISMATRIX," + "CAST(SERVERTOCLIENT0 AS NUMBER(38,15)) AS SERVERTOCLIENT0," + "CAST(SERVERTOCLIENT1 AS NUMBER(38,15)) AS SERVERTOCLIENT1 from table" 原文：http://www.cnblogs.com/nidongde/p/5195787.html