Linq 简明教程

using System;
using System.Linq;

class Program {
   static void Main() {

      string[] words = {"hello", "wonderful", "LINQ", "beautiful", "world"};

      //Get only short words
      var shortWords = from word in words where word.Length <= 5 select word;

      //Print each word out
      foreach (var word in shortWords) {
         Console.WriteLine(word);
      }

      Console.ReadLine();
   }
}

Module Module1
   Sub Main()
      Dim words As String() = {"hello", "wonderful", "LINQ", "beautiful", "world"}

      ' Get only short words
      Dim shortWords = From word In words _ Where word.Length <= 5 _ Select word

      ' Print each word out.

      For Each word In shortWords
         Console.WriteLine(word)
      Next

      Console.ReadLine()
   End Sub
End Module

hello
LINQ
world

var longWords = words.Where( w ⇒ w.length > 10);
Dim longWords = words.Where(Function(w) w.length > 10)

var longwords = from w in words where w.length > 10;
Dim longwords = from w in words where w.length > 10

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Operators {
   class LINQQueryExpressions {
      static void Main() {

         // Specify the data source.
         int[] scores = new int[] { 97, 92, 81, 60 };

         // Define the query expression.
         IEnumerable<int> scoreQuery = from score in scores where score > 80 select score;

         // Execute the query.

         foreach (int i in scoreQuery) {
            Console.Write(i + " ");
         }

         Console.ReadLine();
      }
   }
}

97 92 81

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("\nPress 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

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

Press any key to continue.

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("\nPress 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

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

Press any key to continue.

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("\nPress 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

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.

using System;
using System.Collections.Generic;
using System.Linq;

namespace LINQtoObjects {
   class Department {
      public int DepartmentId { get; set; }
      public string Name { get; set; }
   }

   class LinqToObjects {
      static void Main(string[] args) {

         List<Department> departments = new List<Department>();

         departments.Add(new Department { DepartmentId = 1, Name = "Account" });
         departments.Add(new Department { DepartmentId = 2, Name = "Sales" });
         departments.Add(new Department { DepartmentId = 3, Name = "Marketing" });

         var departmentList = from d in departments
                              select d;

         foreach (var dept in departmentList) {
            Console.WriteLine("Department Id = {0} , Department Name = {1}",
               dept.DepartmentId, dept.Name);
         }

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

Imports System.Collections.Generic
Imports System.Linq

Module Module1

   Sub Main(ByVal args As String())

      Dim account As New Department With {.Name = "Account", .DepartmentId = 1}
      Dim sales As New Department With {.Name = "Sales", .DepartmentId = 2}
      Dim marketing As New Department With {.Name = "Marketing", .DepartmentId = 3}

      Dim departments As New System.Collections.Generic.List(Of Department)(New Department() {account, sales, marketing})

      Dim departmentList = From d In departments

      For Each dept In departmentList
         Console.WriteLine("Department Id = {0} , Department Name = {1}", dept.DepartmentId, dept.Name)
      Next

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

   Class Department
      Public Property Name As String
      Public Property DepartmentId As Integer
   End Class

End Module

Department Id = 1, Department Name = Account
Department Id = 2, Department Name = Sales
Department Id = 3, Department Name = Marketing

Press any key to continue.

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace LINQtoDataset {
   class Program {
      static void Main(string[] args) {

         string connectString = System.Configuration.ConfigurationManager.ConnectionStrings["LinqToSQLDBConnectionString"].ToString();

         string sqlSelect = "SELECT * FROM Department;" + "SELECT * FROM Employee;";

         // Create the data adapter to retrieve data from the database
         SqlDataAdapter da = new SqlDataAdapter(sqlSelect, connectString);

         // Create table mappings
         da.TableMappings.Add("Table", "Department");
         da.TableMappings.Add("Table1", "Employee");

         // Create and fill the DataSet
         DataSet ds = new DataSet();
         da.Fill(ds);

         DataRelation dr = ds.Relations.Add("FK_Employee_Department",
                           ds.Tables["Department"].Columns["DepartmentId"],
                           ds.Tables["Employee"].Columns["DepartmentId"]);

         DataTable department = ds.Tables["Department"];
         DataTable employee = ds.Tables["Employee"];

         var query = from d in department.AsEnumerable()
                     join e in employee.AsEnumerable()
                     on d.Field<int>("DepartmentId") equals
                     e.Field<int>("DepartmentId")
                     select new {
                        EmployeeId = e.Field<int>("EmployeeId"),
                        Name = e.Field<string>("Name"),
                        DepartmentId = d.Field<int>("DepartmentId"),
                        DepartmentName = d.Field<string>("Name")
                     };

         foreach (var q in query) {
            Console.WriteLine("Employee Id = {0} , Name = {1} , Department Name = {2}",
               q.EmployeeId, q.Name, q.DepartmentName);
         }

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

Imports System.Data.SqlClient
Imports System.Linq

Module LinqToDataSet

   Sub Main()

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

      Dim sqlSelect As String = "SELECT * FROM Department;" + "SELECT * FROM Employee;"
      Dim sqlCnn As SqlConnection = New SqlConnection(connectString)
      sqlCnn.Open()

      Dim da As New SqlDataAdapter
      da.SelectCommand = New SqlCommand(sqlSelect, sqlCnn)

      da.TableMappings.Add("Table", "Department")
      da.TableMappings.Add("Table1", "Employee")

      Dim ds As New DataSet()
      da.Fill(ds)

      Dim dr As DataRelation = ds.Relations.Add("FK_Employee_Department", ds.Tables("Department").Columns("DepartmentId"), ds.Tables("Employee").Columns("DepartmentId"))

      Dim department As DataTable = ds.Tables("Department")
      Dim employee As DataTable = ds.Tables("Employee")

      Dim query = From d In department.AsEnumerable()
                  Join e In employee.AsEnumerable() On d.Field(Of Integer)("DepartmentId") Equals
                  e.Field(Of Integer)("DepartmentId")
                  Select New Person With { _
                        .EmployeeId = e.Field(Of Integer)("EmployeeId"),
                        .EmployeeName = e.Field(Of String)("Name"),
                        .DepartmentId = d.Field(Of Integer)("DepartmentId"),
                        .DepartmentName = d.Field(Of String)("Name")
                  }

      For Each e In query
         Console.WriteLine("Employee Id = {0} , Name = {1} , Department Name = {2}", e.EmployeeId, e.EmployeeName, e.DepartmentName)
      Next

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

   End Sub

   Class Person
      Public Property EmployeeId As Integer
      Public Property EmployeeName As String
      Public Property DepartmentId As Integer
      Public Property DepartmentName As String
   End Class

End Module

Employee Id = 1, Name = William, Department Name = Account
Employee Id = 2, Name = Benjamin, Department Name = Account
Employee Id = 3, Name = Miley, Department Name = Sales

Press any key to continue.

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace LinqToDataset {
   class SingleTable {
      static void Main(string[] args) {

         string connectString = System.Configuration.ConfigurationManager.ConnectionStrings["LinqToSQLDBConnectionString"].ToString();

         string sqlSelect = "SELECT * FROM Department;";

         // Create the data adapter to retrieve data from the database
         SqlDataAdapter da = new SqlDataAdapter(sqlSelect, connectString);

         // Create table mappings
         da.TableMappings.Add("Table", "Department");

         // Create and fill the DataSet
         DataSet ds = new DataSet();
         da.Fill(ds);

         DataTable department = ds.Tables["Department"];

         var query = from d in department.AsEnumerable()
         select new {
            DepartmentId = d.Field<int>("DepartmentId"),
            DepartmentName = d.Field<string>("Name")
         };

         foreach (var q in query) {
            Console.WriteLine("Department Id = {0} , Name = {1}",
               q.DepartmentId, q.DepartmentName);
         }

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

Imports System.Data.SqlClient
Imports System.Linq

Module LinqToDataSet

   Sub Main()

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

      Dim sqlSelect As String = "SELECT * FROM Department;"
      Dim sqlCnn As SqlConnection = New SqlConnection(connectString)
      sqlCnn.Open()

      Dim da As New SqlDataAdapter
      da.SelectCommand = New SqlCommand(sqlSelect, sqlCnn)

      da.TableMappings.Add("Table", "Department")
      Dim ds As New DataSet()
      da.Fill(ds)

      Dim department As DataTable = ds.Tables("Department")

      Dim query = From d In department.AsEnumerable()
      Select New DepartmentDetail With {
         .DepartmentId = d.Field(Of Integer)("DepartmentId"),
            .DepartmentName = d.Field(Of String)("Name")
      }

      For Each e In query
         Console.WriteLine("Department Id = {0} , Name = {1}", e.DepartmentId, e.DepartmentName)
      Next

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

   Public Class DepartmentDetail
      Public Property DepartmentId As Integer
      Public Property DepartmentName As String
   End Class

End Module

Department Id = 1, Name = Account
Department Id = 2, Name = Sales
Department Id = 3, Name = Pre-Sales
Department Id = 4, Name = Marketing

Press any key to continue.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Xml.Linq;

namespace LINQtoXML {
   class ExampleOfXML {
      static void Main(string[] args) {

         string myXML = @"<Departments>
                       <Department>Account</Department>
                       <Department>Sales</Department>
                       <Department>Pre-Sales</Department>
                       <Department>Marketing</Department>
                       </Departments>";

         XDocument xdoc = new XDocument();
         xdoc = XDocument.Parse(myXML);

         var result = xdoc.Element("Departments").Descendants();

         foreach (XElement item in result) {
            Console.WriteLine("Department Name - " + item.Value);
         }

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

Imports System.Collections.Generic
Imports System.Linq
Imports System.Xml.Linq

Module Module1

   Sub Main(ByVal args As String())

      Dim myXML As String = "<Departments>" & vbCr & vbLf &
                           "<Department>Account</Department>" & vbCr & vbLf &
                           "<Department>Sales</Department>" & vbCr & vbLf &
                           "<Department>Pre-Sales</Department>" & vbCr & vbLf &
                           "<Department>Marketing</Department>" & vbCr & vbLf &
                           "</Departments>"

      Dim xdoc As New XDocument()
      xdoc = XDocument.Parse(myXML)

      Dim result = xdoc.Element("Departments").Descendants()

      For Each item As XElement In result
         Console.WriteLine("Department Name - " + item.Value)
      Next

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

   End Sub

End Module

Department Name - Account
Department Name - Sales
Department Name - Pre-Sales
Department Name - Marketing

Press any key to continue.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Xml.Linq;

namespace LINQtoXML {
   class ExampleOfXML {
      static void Main(string[] args) {

         string myXML = @"<Departments>
                       <Department>Account</Department>
                       <Department>Sales</Department>
                       <Department>Pre-Sales</Department>
                       <Department>Marketing</Department>
                       </Departments>";

         XDocument xdoc = new XDocument();
         xdoc = XDocument.Parse(myXML);

         //Add new Element
         xdoc.Element("Departments").Add(new XElement("Department", "Finance"));

         //Add new Element at First
         xdoc.Element("Departments").AddFirst(new XElement("Department", "Support"));

         var result = xdoc.Element("Departments").Descendants();

         foreach (XElement item in result) {
            Console.WriteLine("Department Name - " + item.Value);
         }

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

Imports System.Collections.Generic
Imports System.Linq
Imports System.Xml.Linq

Module Module1

   Sub Main(ByVal args As String())

      Dim myXML As String = "<Departments>" & vbCr & vbLf &
     	                   "<Department>Account</Department>" & vbCr & vbLf &
     	                   "<Department>Sales</Department>" & vbCr & vbLf &
     	                   "<Department>Pre-Sales</Department>" & vbCr & vbLf &
     	                   "<Department>Marketing</Department>" & vbCr & vbLf &
     	                   "</Departments>"

      Dim xdoc As New XDocument()
      xdoc = XDocument.Parse(myXML)

      xdoc.Element("Departments").Add(New XElement("Department", "Finance"))

      xdoc.Element("Departments").AddFirst(New XElement("Department", "Support"))

      Dim result = xdoc.Element("Departments").Descendants()

      For Each item As XElement In result
         Console.WriteLine("Department Name - " + item.Value)
      Next

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

   End Sub

End Module

Department Name - Support
Department Name - Account
Department Name - Sales
Department Name - Pre-Sales
Department Name - Marketing
Department Name - Finance

Press any key to continue.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Xml.Linq;

namespace LINQtoXML {
   class ExampleOfXML {
      static void Main(string[] args) {

         string myXML = @"<Departments>
                       <Department>Support</Department>
                       <Department>Account</Department>
                       <Department>Sales</Department>
                       <Department>Pre-Sales</Department>
                       <Department>Marketing</Department>
                       <Department>Finance</Department>
                       </Departments>";

         XDocument xdoc = new XDocument();
         xdoc = XDocument.Parse(myXML);

         //Remove Sales Department
         xdoc.Descendants().Where(s =>s.Value == "Sales").Remove();

         var result = xdoc.Element("Departments").Descendants();

         foreach (XElement item in result) {
            Console.WriteLine("Department Name - " + item.Value);
         }

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

Imports System.Collections.Generic
Imports System.Linq
Imports System.Xml.Linq

Module Module1

   Sub Main(args As String())

      Dim myXML As String = "<Departments>" & vbCr & vbLf &
     	                   "<Department>Support</Department>" & vbCr & vbLf &
     	                   "<Department>Account</Department>" & vbCr & vbLf &
     	                   "<Department>Sales</Department>" & vbCr & vbLf &
     	                   "<Department>Pre-Sales</Department>" & vbCr & vbLf &
     	                   "<Department>Marketing</Department>" & vbCr & vbLf &
     	                   "<Department>Finance</Department>" & vbCr & vbLf &
                           "</Departments>"

      Dim xdoc As New XDocument()
      xdoc = XDocument.Parse(myXML)

      xdoc.Descendants().Where(Function(s) s.Value = "Sales").Remove()

      Dim result = xdoc.Element("Departments").Descendants()

      For Each item As XElement In result
         Console.WriteLine("Department Name - " + item.Value)
      Next

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

   End Sub

End Module

Department Name - Support
Department Name - Account
Department Name - Pre-Sales
Department Name - Marketing
Department Name - Finance

Press any key to continue.

//Get the average of the odd Fibonacci numbers in the series...

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace lambdaexample {
   class Program {
      static void Main(string[] args) {

         int[] fibNum = { 1, 1, 2, 3, 5, 8, 13, 21, 34 };
         double averageValue = fibNum.Where(num ⇒ num % 2 == 1).Average();
         Console.WriteLine(averageValue);
         Console.ReadLine();
      }
   }
}

Module Module1

   Sub Main()

      Dim fibNum As Integer() = {1, 1, 2, 3, 5, 8, 13, 21, 34}
      Dim averageValue As Double = fibNum.Where(Function(num) num Mod 2 = 1).Average()

      Console.WriteLine(averageValue)
      Console.ReadLine()

   End Sub

End Module

7.33333333333333

using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Linq.Expressions;

namespace lambdaexample {
   class Program {
      static void Main(string[] args) {
         int[] source = new[] { 3, 8, 4, 6, 1, 7, 9, 2, 4, 8 };

         foreach (int i in source.Where(x ⇒
            {
               if (x <= 3)
                  return true;
               else if (x >= 7)
                  return true;
               return false;
            }
         ))
        Console.WriteLine(i);
        Console.ReadLine();
      }
   }
}

3
8
1
7
9
2
8