LINQ - SQL

LINQ to SQL 为将关系数据作为对象进行管理提供了一种基础结构（运行时）。它是 .NET Framework 3.5 版的一个组件，能够将对象模型的语言集成查询转换为 SQL。然后，这些查询被发送到数据库以供执行。从数据库获取结果后，LINQ to SQL 再次将它们转换为对象。

LINQ To SQL 简介

对于大多数 ASP.NET 开发人员来说，LINQ to SQL（也称为 DLINQ）是语言集成查询中令人兴奋的一部分，因为它允许使用常见的 LINQ 表达式查询 SQL 服务器数据库中的数据。它还允许更新、删除和插入数据，但它唯一的缺点是它仅限于 SQL 服务器数据库。但是，LINQ to SQL 相对于 ADO.NET 有很多好处，例如降低了复杂性、减少了几行代码等等。

下面是显示 LINQ to SQL 执行架构的图表。

如何使用 LINQ to SQL？

步骤 1 − 与数据库服务器建立新的"数据连接"。查看 &arrar; 服务器资源管理器 &arrar; 数据连接 &arrar; 添加连接

步骤 2 −添加 LINQ To SQL 类文件

步骤 3 − 从数据库中选择表并将其拖放到新的 LINQ to SQL 类文件中。

步骤 4 − 将表添加到类文件。

使用 LINQ to SQL 进行查询

使用 LINQ to SQL 执行查询的规则与标准 LINQ 查询的规则类似，即查询可以延迟执行或立即执行。有各种组件在使用 LINQ to SQL 执行查询时发挥作用，这些组件如下。

LINQ to SQL API − 代表应用程序请求查询执行并将其发送到 LINQ to SQL 提供程序。
LINQ to SQL 提供程序 − 将查询转换为 Transact SQL (T-SQL) 并将新查询发送到 ADO 提供程序进行执行。
ADO 提供程序 −执行查询后，将结果以 DataReader 的形式发送到 LINQ to SQL 提供程序，后者又将其转换为用户对象的形式。

需要注意的是，在执行 LINQ to SQL 查询之前，必须通过 DataContext 类连接到数据源。

使用 LINQ To SQL 插入、更新和删除

添加或插入

using System;
using System.Linq;

namespace LINQtoSQL {
   class LinqToSQLCRUD {
      static void Main(string[] args) {
      
         string connectString = System.Configuration.ConfigurationManager.ConnectionStrings["LinqToSQLDBConnectionString"].ToString();

         LinqToSQLDataContext db = new LinqToSQLDataContext(connectString);           

         //Create new Employee
		 
         Employee newEmployee = new Employee();
         newEmployee.Name = "Michael";
         newEmployee.Email = "yourname@companyname.com";
         newEmployee.ContactNo = "343434343";
         newEmployee.DepartmentId = 3;
         newEmployee.Address = "Michael - USA";

         //Add new Employee to database
         db.Employees.InsertOnSubmit(newEmployee);

         //Save changes to Database.
         db.SubmitChanges();

         //Get new Inserted Employee            
         Employee insertedEmployee = db.Employees.FirstOrDefault(e ⇒e.Name.Equals("Michael"));

         Console.WriteLine("Employee Id = {0} , Name = {1}, Email = {2}, ContactNo = {3}, Address = {4}",
                          insertedEmployee.EmployeeId, insertedEmployee.Name, insertedEmployee.Email, 
                          insertedEmployee.ContactNo, insertedEmployee.Address);

         Console.WriteLine("
Press any key to continue.");
         Console.ReadKey();
      }
   }
}

Module Module1

   Sub Main()
   
      Dim connectString As String = System.Configuration.ConfigurationManager.ConnectionStrings("LinqToSQLDBConnectionString").ToString()

      Dim db As New LinqToSQLDataContext(connectString)

      Dim newEmployee As New Employee()
	  
      newEmployee.Name = "Michael"
      newEmployee.Email = "yourname@companyname.com"
      newEmployee.ContactNo = "343434343"
      newEmployee.DepartmentId = 3
      newEmployee.Address = "Michael - USA"
     
      db.Employees.InsertOnSubmit(newEmployee)
     
      db.SubmitChanges()
     
      Dim insertedEmployee As Employee = db.Employees.FirstOrDefault(Function(e) e.Name.Equals("Michael"))

      Console.WriteLine("Employee Id = {0} , Name = {1}, Email = {2}, ContactNo = {3}, 
         Address = {4}", insertedEmployee.EmployeeId, insertedEmployee.Name,
         insertedEmployee.Email, insertedEmployee.ContactNo, insertedEmployee.Address)

      Console.WriteLine(vbLf & "Press any key to continue.")
      Console.ReadKey()
	 
   End Sub
  
End Module

当编译并运行上述 C# 或 VB 代码时，会产生以下结果 −

Emplyee ID = 4, Name = Michael, Email = yourname@companyname.com, ContactNo = 
343434343, Address = Michael - USA

Press any key to continue.

Update

using System;
using System.Linq;

namespace LINQtoSQL {
   class LinqToSQLCRUD {
      static void Main(string[] args) {
      
         string connectString = System.Configuration.ConfigurationManager.ConnectionStrings["LinqToSQLDBConnectionString"].ToString();

         LinqToSQLDataContext db = new LinqToSQLDataContext(connectString);

         //Get Employee for update
         Employee employee = db.Employees.FirstOrDefault(e =>e.Name.Equals("Michael"));

         employee.Name = "George Michael";
         employee.Email = "yourname@companyname.com";
         employee.ContactNo = "99999999";
         employee.DepartmentId = 2;
         employee.Address = "Michael George - UK";

         //Save changes to Database.
         db.SubmitChanges();

         //Get Updated Employee            
         Employee updatedEmployee = db.Employees.FirstOrDefault(e ⇒e.Name.Equals("George Michael"));

         Console.WriteLine("Employee Id = {0} , Name = {1}, Email = {2}, ContactNo = {3}, Address = {4}",
                          updatedEmployee.EmployeeId, updatedEmployee.Name, updatedEmployee.Email, 
                          updatedEmployee.ContactNo, updatedEmployee.Address);

         Console.WriteLine("
Press any key to continue.");
         Console.ReadKey();
      }
   }
}

Module Module1

   Sub Main()
  
      Dim connectString As String = System.Configuration.ConfigurationManager.ConnectionStrings("LinqToSQLDBConnectionString").ToString()

      Dim db As New LinqToSQLDataContext(connectString)

      Dim employee As Employee = db.Employees.FirstOrDefault(Function(e) e.Name.Equals("Michael"))

      employee.Name = "George Michael"
      employee.Email = "yourname@companyname.com"
      employee.ContactNo = "99999999"
      employee.DepartmentId = 2
      employee.Address = "Michael George - UK"

      db.SubmitChanges()
          
      Dim updatedEmployee As Employee = db.Employees.FirstOrDefault(Function(e) e.Name.Equals("George Michael"))

      Console.WriteLine("Employee Id = {0} , Name = {1}, Email = {2}, ContactNo = {3},
         Address = {4}", updatedEmployee.EmployeeId, updatedEmployee.Name, 
         updatedEmployee.Email, updatedEmployee.ContactNo, updatedEmployee.Address)

      Console.WriteLine(vbLf & "Press any key to continue.")
      Console.ReadKey()
	  
   End Sub
   
End Module

当编译并运行上述 C# 或 VB 代码时，会产生以下结果 −

Emplyee ID = 4, Name = George Michael, Email = yourname@companyname.com, ContactNo = 
999999999, Address = Michael George - UK

Press any key to continue.

Delete

using System;
using System.Linq;

namespace LINQtoSQL {
   class LinqToSQLCRUD {
      static void Main(string[] args) {
      
         string connectString = System.Configuration.ConfigurationManager.ConnectionStrings["LinqToSQLDBConnectionString"].ToString();

         LinqToSQLDataContext db = newLinqToSQLDataContext(connectString);

         //Get Employee to Delete
         Employee deleteEmployee = db.Employees.FirstOrDefault(e ⇒e.Name.Equals("George Michael"));

         //Delete Employee
         db.Employees.DeleteOnSubmit(deleteEmployee);

         //Save changes to Database.
         db.SubmitChanges();

         //Get All Employee from Database
         var employeeList = db.Employees;
         foreach (Employee employee in employeeList) {
            Console.WriteLine("Employee Id = {0} , Name = {1}, Email = {2}, ContactNo = {3}",
               employee.EmployeeId, employee.Name, employee.Email, employee.ContactNo);
         }            

         Console.WriteLine("
Press any key to continue.");
         Console.ReadKey();
      }
   }
}

Module Module1

   Sub Main()
   
      Dim connectString As String = System.Configuration.ConfigurationManager.ConnectionStrings("LinqToSQLDBConnectionString").ToString()

      Dim db As New LinqToSQLDataContext(connectString)

      Dim deleteEmployee As Employee = db.Employees.FirstOrDefault(Function(e) e.Name.Equals("George Michael"))

      db.Employees.DeleteOnSubmit(deleteEmployee)

      db.SubmitChanges()

      Dim employeeList = db.Employees
	  
      For Each employee As Employee In employeeList
         Console.WriteLine("Employee Id = {0} , Name = {1}, Email = {2}, ContactNo = {3}",
            employee.EmployeeId, employee.Name, employee.Email, employee.ContactNo)
      Next 

      Console.WriteLine(vbLf & "Press any key to continue.")
      Console.ReadKey()
   End Sub
   
End Module

当编译并运行上述 C# 或 VB 代码时，会产生以下结果 −

Emplyee ID = 1, Name = William, Email = abc@gy.co, ContactNo = 999999999
Emplyee ID = 2, Name = Miley, Email = amp@esds.sds, ContactNo = 999999999
Emplyee ID = 3, Name = Benjamin, Email = asdsad@asdsa.dsd, ContactNo = 

Press any key to continue.

LINQ 教程

LINQ 其他

LINQ - SQL

LINQ To SQL 简介

如何使用 LINQ to SQL？

使用 LINQ to SQL 进行查询

使用 LINQ To SQL 插入、更新和删除

添加或插入

Update

Delete

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