c# Linq to sql 基本查询例子

c# Linq to sql 基本查询例子

分类： .net 2010-11-18 10:06 801人阅读 评论(1) 收藏 举报

准备工作：1.使用微软的例子数据库-Northwind,没有的可以到微软挂官网去下,附件到sql server2005数据库中

2.使用微软O/R设计器，将Northwind映射到项目中，以下实例在此环境下进行,使用vs2008

以下为代码:

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using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using DBClass;//此处为O/R映射Northwind

using System.Data.Linq;

using System.Data.Linq.SqlClient;

namespace Linq_to_Sql_Demo1

{

class Program

{

static void Main(string[] args)

{

LinqForLike();

}

#region linq中select语句的使用

public static void SqlFroSelectOne()

{

NorthwindDataContext db = new NorthwindDataContext();

var q = from c in db.Customers where c.City == "London" select new { c.CompanyName, c.City };

//上下两句表达意思是一样的，上面为标准查询语句，下面为级连表达式

// var q = db.Customers.Where(c => c.City == "London").Select(c => c.ContactName);

/* 手动填写数据库对象后的方法

DataContext dc = new DataContext("server=.//sql2005;database=Northwind;uid=sa;pwd=king_860119");

var q = from c in dc.GetTable<Customers>() where c.City == "London" select c.CompanyName;

*/

foreach (var c in q)

{

Console.WriteLine(c);

}

Console.ReadLine();

}

#endregion

#region linq中select语句的使用2

public static void SqlFroSelectTwo()

{

NorthwindDataContext dc = new NorthwindDataContext();

var q=from s in dc.Customers select new{城市名称=s.City};

//在这里相当于声明一个匿名类q,q中存在属性“城市名称”,而其中S为一条条的dc.Customers对象

//其中“城市名称”这个属性当当与对S.city的重命名一样

foreach(var a in q)

{

Console.WriteLine(a);

}

Console.Read();

}

#endregion

#region linq中select语句的使用3

public static void SqlFroSelectThree()

{

NorthwindDataContext dc = new NorthwindDataContext();

var q=from s in dc.Products select new {s.ProductName,我的条件=s.UnitsInStock-s.UnitsOnOrder<0?"out":"in"};

foreach(var a in q)

{

Console.WriteLine(a);

}

Console.Read();

}

#endregion

#region linq中where语句的使用1

public static void SqlFroWhereOne()

{

NorthwindDataContext db = new NorthwindDataContext();

var q =

from p in db.Products

where p.UnitPrice > 10m || p.Discontinued

select p;

foreach (var a in q)

{

Console.WriteLine(a.Categories.CategoryID);

}

Console.Read();

}

#endregion

#region linq中order语句的使用1

public static void SqlFroOrderOne()

{

NorthwindDataContext db = new NorthwindDataContext();

var q = from s in db.Employees orderby s.EmployeeID descending select new { s.EmployeeID,s.FirstName,s.LastName};

//orderby子句在select子句前面，与where等子句位置无要求

foreach (var s in q)

{

Console.WriteLine(s.ToString());

}

Console.Read();

}

#endregion

#region Linq中GroupBy语句的使用1

public static void SqlFroGroupByOne()

{

NorthwindDataContext db = new NorthwindDataContext();

var q = from p in db.Products group p by p.CategoryID into g select g;

foreach (var gp in q)

{

if (gp.Key == 7)

{

foreach (var p in gp)

{

//do something

}

}

}

Console.ReadKey();

}

#endregion

#region Linq中GroupBy语句的使用2

public static void SqlForGroupByTwo()

{

NorthwindDataContext db = new NorthwindDataContext();

var q = from p in db.Products group p by p.CategoryID into g select new { CategoryID = g.Key, g };

foreach (var gp in q)

{

//do something

}

}

#endregion

#region Linq中GroupBy语句的使用30-聚合函数的使用

public static void SqlForGroupByThree()

{

NorthwindDataContext db = new NorthwindDataContext();

var q = from p in db.Products group p by p.CategoryID into g select new { g.Key, TotalPrice = g.Sum(p => p.UnitPrice) };

foreach (var a in q)

{

Console.WriteLine(a);

}

Console.Read();

}

#endregion

#region Linq中Join语句的使用1

public static void LinqForJoinOne()

{

NorthwindDataContext db = new NorthwindDataContext();

var q = from p in db.Customers join o in db.Orders on p.CustomerID equals o.CustomerID select new { p.CustomerID, o.EmployeeID };

//下面注释的语句为此句的lambda的写法

// var q = db.Customers.Join(db.Orders, p => p.CustomerID, o => o.CustomerID, (p, o) => new { p.CustomerID, o.EmployeeID });

foreach (var s in q)

{

Console.WriteLine(s);

}

Console.Read();

}

#endregion

#region Linq中In语句的使用

public static void LinqForInOne()

{

NorthwindDataContext db = new NorthwindDataContext();

string[] customerID_Set = new string[] { "AROUT", "BOLID", "FISSA" };

var q = from s in db.Orders where customerID_Set.Contains(s.CustomerID) select s.EmployeeID;

//相当于sql中的in，意思就是从这个in的集合中取出，如果not in 就在集合的前面加上！

foreach (var a in q)

{

Console.WriteLine(a);

}

Console.Read();

}

#endregion

#region Linq中Like语句的使用

public static void LinqForLike()

{

NorthwindDataContext db = new NorthwindDataContext();

//中间部分包含And的

var q = from s in db.Customers where s.ContactName.Contains("And") select s.ContactName;

//开头部分包含A的

var p = from s in db.Customers where s.ContactName.StartsWith("A") select s.ContactName;

//结束部分包含g的

var a = from s in db.Customers where s.ContactName.EndsWith("g") select s.ContactName;

//另外的一种写法，需要命名空间System.Data.Linq.SqlClient

var c = from s in db.Customers where SqlMethods.Like(s.ContactName, "%g") select s.ContactName;

foreach (var b in c)

{

Console.WriteLine(b);

}

Console.Read();

}

#endregion

}

}

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#region linq中insert语句的使用

public static void LinqForInsert()

{

NorthwindDataContext db = new NorthwindDataContext();

var rgdata = new Region { RegionID = 5, RegionDescription = "test" };

try

{

db.Region.InsertOnSubmit(rgdata);//插入数据

db.SubmitChanges();//提交更改

}

catch (Exception err)

{

Console.WriteLine(err.Message);

}

Console.Read();

}

#endregion

#region Linq中update语句的使用

public static void LinqForUpdata()

{

NorthwindDataContext db = new NorthwindDataContext();

var o = from c in db.Region where c.RegionID == 5 select c;

foreach (var item in o)

{

if(item.RegionID==5)

item.RegionDescription = "test改过了";

}

db.SubmitChanges();

}

#endregion

#region Linq中del语句的使用

public static void LinqForDel()

{

NorthwindDataContext db = new NorthwindDataContext();

var q = from c in db.Region where c.RegionID == 5 select c;

foreach (var item in q)

{

db.Region.DeleteOnSubmit(item);

}

db.SubmitChanges();

}

#endregion

#region linq中insert语句的使用
public static void LinqForInsert()
{
NorthwindDataContext db = new NorthwindDataContext();

var rgdata = new Region { RegionID = 5, RegionDescription = "test" };

try
{
db.Region.InsertOnSubmit(rgdata);//插入数据
db.SubmitChanges();//提交更改
}
catch (Exception err)
{
Console.WriteLine(err.Message);
}
Console.Read();
}
#endregion

#region Linq中update语句的使用
public static void LinqForUpdata()
{
NorthwindDataContext db = new NorthwindDataContext();

var o = from c in db.Region where c.RegionID == 5 select c;

foreach (var item in o)
{
if(item.RegionID==5)
item.RegionDescription = "test改过了";
}

db.SubmitChanges();

}
#endregion

#region Linq中del语句的使用
public static void LinqForDel()
{
NorthwindDataContext db = new NorthwindDataContext();

var q = from c in db.Region where c.RegionID == 5 select c;

foreach (var item in q)
{
db.Region.DeleteOnSubmit(item);
}
db.SubmitChanges();
}
#endregion