Teilen über

Exemplarische Vorgehensweise: Verwenden von BatchBlock und BatchedJoinBlock zur Verbesserung der Effizienz

Die TPL-Datenflussbibliothek stellt die System.Threading.Tasks.Dataflow.BatchBlock<T> und System.Threading.Tasks.Dataflow.BatchedJoinBlock<T1,T2> klassen bereit, sodass Sie Daten aus einer oder mehreren Quellen empfangen und puffern und dann diese gepufferten Daten als eine Sammlung verteilen können. Dieser Batchverarbeitungsmechanismus ist nützlich, wenn Sie Daten aus einer oder mehreren Quellen sammeln und dann mehrere Datenelemente als Batch verarbeiten. Betrachten Sie beispielsweise eine Anwendung, die Datenflüsse verwendet, um Datensätze in eine Datenbank einzufügen. Dieser Vorgang kann effizienter sein, wenn mehrere Elemente gleichzeitig eingefügt werden, anstatt jeweils einzeln. In diesem Dokument wird beschrieben, wie Sie die BatchBlock<T> Klasse verwenden, um die Effizienz solcher Datenbankeinfügungsvorgänge zu verbessern. Außerdem wird beschrieben, wie die BatchedJoinBlock<T1,T2> Klasse verwendet wird, um sowohl die Ergebnisse als auch alle Ausnahmen zu erfassen, die auftreten, wenn das Programm aus einer Datenbank liest.

Hinweis

Die TPL-Datenflussbibliothek (der System.Threading.Tasks.Dataflow Namespace) ist in .NET 6 und höheren Versionen enthalten. Für .NET Framework- und .NET Standard-Projekte müssen Sie das 📦 NuGet-Paket "System.Threading.Tasks.Dataflow" installieren.

Voraussetzungen

  1. Lesen Sie den Abschnitt "Verknüpfungsblöcke" im Dataflow-Dokument , bevor Sie mit dieser exemplarischen Vorgehensweise beginnen.

  2. Stellen Sie sicher, dass Sie über eine Kopie der Northwind-Datenbank Northwind.sdf verfügen, die auf Ihrem Computer verfügbar ist.

    Von Bedeutung

    In einigen Versionen von Windows können Sie keine Verbindung mit Northwind.sdf herstellen, wenn Visual Studio im Nicht-Administratormodus ausgeführt wird. Um eine Verbindung mit Northwind.sdf herzustellen, starten Sie Visual Studio oder eine Entwickler-Eingabeaufforderung für Visual Studio im Modus "Als Administrator ausführen ".

Erstellen der Konsolenanwendung

  1. Erstellen Sie in Visual Studio ein Visual C#- oder Visual Basic-Konsolenanwendungsprojekt . In diesem Dokument wird das Projekt benannt DataflowBatchDatabase.

  2. Stellen Sie sicher, dass Form1.cs (Form1.vb für Visual Basic) die folgenden using (Imports in Visual Basic)-Anweisungen enthält.

    using System;
using System.Collections.Generic;
using System.Data.SqlClient;
using System.Diagnostics;
using System.IO;
using System.Threading.Tasks.Dataflow;

    Imports System.Collections.Generic
Imports System.Data.SqlClient
Imports System.Data.SqlServerCe
Imports System.Diagnostics
Imports System.IO
Imports System.Threading.Tasks.Dataflow

  3. Fügen Sie der Klasse Program die folgenden Datenmitglieder hinzu.

    // The number of employees to add to the database.
// TODO: Change this value to experiment with different numbers of
// employees to insert into the database.
static readonly int insertCount = 256;

// The size of a single batch of employees to add to the database.
// TODO: Change this value to experiment with different batch sizes.
static readonly int insertBatchSize = 96;

// The source database file.
// TODO: Change this value if Northwind.sdf is at a different location
// on your computer.
static readonly string sourceDatabase =
   @"C:\...\Northwind.sdf";

// TODO: Change this value if you require a different temporary location.
static readonly string scratchDatabase =
   @"C:\Temp\Northwind.sdf";

    ' The number of employees to add to the database.
' TODO: Change this value to experiment with different numbers of 
' employees to insert into the database.
Private Shared ReadOnly insertCount As Integer = 256

' The size of a single batch of employees to add to the database.
' TODO: Change this value to experiment with different batch sizes.
Private Shared ReadOnly insertBatchSize As Integer = 96

' The source database file.
' TODO: Change this value if Northwind.sdf is at a different location
' on your computer.
Private Shared ReadOnly sourceDatabase As String = "C:\Program Files\Microsoft SQL Server Compact Edition\v3.5\Samples\Northwind.sdf"

' TODO: Change this value if you require a different temporary location.
Private Shared ReadOnly scratchDatabase As String = "C:\Temp\Northwind.sdf"

Definieren der Mitarbeiterklasse

Fügen Sie der Program Klasse die Employee Klasse hinzu.

// Describes an employee. Each property maps to a
// column in the Employees table in the Northwind database.
// For brevity, the Employee class does not contain
// all columns from the Employees table.
class Employee
{
   public int EmployeeID { get; set; }
   public string LastName { get; set; }
   public string FirstName { get; set; }

   // A random number generator that helps tp generate
   // Employee property values.
   static Random rand = new Random(42);

   // Possible random first names.
   static readonly string[] firstNames = { "Tom", "Mike", "Ruth", "Bob", "John" };
   // Possible random last names.
   static readonly string[] lastNames = { "Jones", "Smith", "Johnson", "Walker" };

   // Creates an Employee object that contains random
   // property values.
   public static Employee Random()
   {
      return new Employee
      {
         EmployeeID = -1,
         LastName = lastNames[rand.Next() % lastNames.Length],
         FirstName = firstNames[rand.Next() % firstNames.Length]
      };
   }
}

' Describes an employee. Each property maps to a 
' column in the Employees table in the Northwind database.
' For brevity, the Employee class does not contain
' all columns from the Employees table.
Private Class Employee
    Public Property EmployeeID() As Integer
    Public Property LastName() As String
    Public Property FirstName() As String

    ' A random number generator that helps tp generate
    ' Employee property values.
    Private Shared rand As New Random(42)

    ' Possible random first names.
    Private Shared ReadOnly firstNames() As String = {"Tom", "Mike", "Ruth", "Bob", "John"}
    ' Possible random last names.
    Private Shared ReadOnly lastNames() As String = {"Jones", "Smith", "Johnson", "Walker"}

    ' Creates an Employee object that contains random 
    ' property values.
    Public Shared Function Random() As Employee
        Return New Employee With {.EmployeeID = -1, .LastName = lastNames(rand.Next() Mod lastNames.Length), .FirstName = firstNames(rand.Next() Mod firstNames.Length)}
    End Function
End Class

Die Employee Klasse enthält drei Eigenschaften, EmployeeID, LastNameund FirstName. Diese Eigenschaften entsprechen den Employee ID, Last Nameund First Name Spalten in der Employees Tabelle in der Northwind-Datenbank. Für diese Demonstration definiert die Employee Klasse auch die Random Methode, die ein Employee Objekt erstellt, das Zufallswerte für seine Eigenschaften enthält.

Definieren von Mitarbeiterdatenbankvorgängen

Fügen Sie der Klasse die ProgramInsertEmployees, GetEmployeeCountund GetEmployeeID Methoden hinzu.

// Adds new employee records to the database.
static void InsertEmployees(Employee[] employees, string connectionString)
{
   using (SqlConnection connection =
      new SqlConnection(connectionString))
   {
      try
      {
         // Create the SQL command.
         SqlCommand command = new SqlCommand(
            "INSERT INTO Employees ([Last Name], [First Name])" +
            "VALUES (@lastName, @firstName)",
            connection);

         connection.Open();
         for (int i = 0; i < employees.Length; i++)
         {
            // Set parameters.
            command.Parameters.Clear();
            command.Parameters.Add("@lastName", employees[i].LastName);
            command.Parameters.Add("@firstName", employees[i].FirstName);

            // Execute the command.
            command.ExecuteNonQuery();
         }
      }
      finally
      {
         connection.Close();
      }
   }
}

// Retrieves the number of entries in the Employees table in
// the Northwind database.
static int GetEmployeeCount(string connectionString)
{
   int result = 0;
   using (SqlConnection sqlConnection =
      new SqlConnection(connectionString))
   {
      SqlCommand sqlCommand = new SqlCommand(
         "SELECT COUNT(*) FROM Employees", sqlConnection);

      sqlConnection.Open();
      try
      {
         result = (int)sqlCommand.ExecuteScalar();
      }
      finally
      {
         sqlConnection.Close();
      }
   }
   return result;
}

// Retrieves the ID of the first employee that has the provided name.
static int GetEmployeeID(string lastName, string firstName,
   string connectionString)
{
   using (SqlConnection connection =
      new SqlConnection(connectionString))
   {
      SqlCommand command = new SqlCommand(
         string.Format(
            "SELECT [Employee ID] FROM Employees " +
            "WHERE [Last Name] = '{0}' AND [First Name] = '{1}'",
            lastName, firstName),
         connection);

      connection.Open();
      try
      {
         return (int)command.ExecuteScalar();
      }
      finally
      {
         connection.Close();
      }
   }
}

' Adds new employee records to the database.
Private Shared Sub InsertEmployees(ByVal employees() As Employee, ByVal connectionString As String)
    Using connection As New SqlConnection(connectionString)
        Try
            ' Create the SQL command.
            Dim command As New SqlCommand("INSERT INTO Employees ([Last Name], [First Name])" & "VALUES (@lastName, @firstName)", connection)

            connection.Open()
            For i As Integer = 0 To employees.Length - 1
                ' Set parameters.
                command.Parameters.Clear()
                command.Parameters.Add("@lastName", employees(i).LastName)
                command.Parameters.Add("@firstName", employees(i).FirstName)

                ' Execute the command.
                command.ExecuteNonQuery()
            Next i
        Finally
            connection.Close()
        End Try
    End Using
End Sub

' Retrieves the number of entries in the Employees table in 
' the Northwind database.
Private Shared Function GetEmployeeCount(ByVal connectionString As String) As Integer
    Dim result As Integer = 0
    Using sqlConnection As New SqlConnection(connectionString)
        Dim sqlCommand As New SqlCommand("SELECT COUNT(*) FROM Employees", sqlConnection)

        sqlConnection.Open()
        Try
            result = CInt(Fix(sqlCommand.ExecuteScalar()))
        Finally
            sqlConnection.Close()
        End Try
    End Using
    Return result
End Function

' Retrieves the ID of the first employee that has the provided name.
Private Shared Function GetEmployeeID(ByVal lastName As String, ByVal firstName As String, ByVal connectionString As String) As Integer
    Using connection As New SqlConnection(connectionString)
        Dim command As New SqlCommand(String.Format("SELECT [Employee ID] FROM Employees " & "WHERE [Last Name] = '{0}' AND [First Name] = '{1}'", lastName, firstName), connection)

        connection.Open()
        Try
            Return CInt(Fix(command.ExecuteScalar()))
        Finally
            connection.Close()
        End Try
    End Using
End Function

Die InsertEmployees Methode fügt der Datenbank neue Mitarbeiterdatensätze hinzu. Die GetEmployeeCount Methode ruft die Anzahl der Einträge in der Employees Tabelle ab. Die GetEmployeeID Methode ruft den Bezeichner des ersten Mitarbeiters ab, der den angegebenen Namen hat. Jede dieser Methoden verwendet eine Verbindungszeichenfolge mit der Northwind-Datenbank.

Hinzufügen von Mitarbeiterdaten zur Datenbank ohne Pufferung

Fügen Sie der Program Klasse die AddEmployees und PostRandomEmployees Method hinzu.

// Posts random Employee data to the provided target block.
static void PostRandomEmployees(ITargetBlock<Employee> target, int count)
{
   Console.WriteLine($"Adding {count} entries to Employee table...");

   for (int i = 0; i < count; i++)
   {
      target.Post(Employee.Random());
   }
}

// Adds random employee data to the database by using dataflow.
static void AddEmployees(string connectionString, int count)
{
   // Create an ActionBlock<Employee> object that adds a single
   // employee entry to the database.
   var insertEmployee = new ActionBlock<Employee>(e =>
      InsertEmployees(new Employee[] { e }, connectionString));

   // Post several random Employee objects to the dataflow block.
   PostRandomEmployees(insertEmployee, count);

   // Set the dataflow block to the completed state and wait for
   // all insert operations to complete.
   insertEmployee.Complete();
   insertEmployee.Completion.Wait();
}

' Posts random Employee data to the provided target block.
Private Shared Sub PostRandomEmployees(ByVal target As ITargetBlock(Of Employee), ByVal count As Integer)
    Console.WriteLine("Adding {0} entries to Employee table...", count)

    For i As Integer = 0 To count - 1
        target.Post(Employee.Random())
    Next i
End Sub

' Adds random employee data to the database by using dataflow.
Private Shared Sub AddEmployees(ByVal connectionString As String, ByVal count As Integer)
    ' Create an ActionBlock<Employee> object that adds a single
    ' employee entry to the database.
    Dim insertEmployee = New ActionBlock(Of Employee)(Sub(e) InsertEmployees(New Employee() {e}, connectionString))

    ' Post several random Employee objects to the dataflow block.
    PostRandomEmployees(insertEmployee, count)

    ' Set the dataflow block to the completed state and wait for 
    ' all insert operations to complete.
    insertEmployee.Complete()
    insertEmployee.Completion.Wait()
End Sub

Die AddEmployees Methode fügt der Datenbank zufällige Mitarbeiterdaten mithilfe von Dataflow hinzu. Es erstellt ein ActionBlock<TInput> Objekt, das die InsertEmployees Methode aufruft, um der Datenbank einen Mitarbeitereintrag hinzuzufügen. Die AddEmployees Methode ruft dann die PostRandomEmployees Methode auf, um mehrere Employee Objekte an das ActionBlock<TInput> Objekt zu posten. Die AddEmployees Methode wartet dann, bis alle Einfügevorgänge abgeschlossen sind.

Verwenden der Pufferung zum Hinzufügen von Mitarbeiterdaten zur Datenbank

Fügen Sie der Program-Klasse die AddEmployeesBatched-Methode hinzu.

// Adds random employee data to the database by using dataflow.
// This method is similar to AddEmployees except that it uses batching
// to add multiple employees to the database at a time.
static void AddEmployeesBatched(string connectionString, int batchSize,
   int count)
{
   // Create a BatchBlock<Employee> that holds several Employee objects and
   // then propagates them out as an array.
   var batchEmployees = new BatchBlock<Employee>(batchSize);

   // Create an ActionBlock<Employee[]> object that adds multiple
   // employee entries to the database.
   var insertEmployees = new ActionBlock<Employee[]>(a =>
      InsertEmployees(a, connectionString));

   // Link the batch block to the action block.
   batchEmployees.LinkTo(insertEmployees);

   // When the batch block completes, set the action block also to complete.
   batchEmployees.Completion.ContinueWith(delegate { insertEmployees.Complete(); });

   // Post several random Employee objects to the batch block.
   PostRandomEmployees(batchEmployees, count);

   // Set the batch block to the completed state and wait for
   // all insert operations to complete.
   batchEmployees.Complete();
   insertEmployees.Completion.Wait();
}

' Adds random employee data to the database by using dataflow.
' This method is similar to AddEmployees except that it uses batching
' to add multiple employees to the database at a time.
Private Shared Sub AddEmployeesBatched(ByVal connectionString As String, ByVal batchSize As Integer, ByVal count As Integer)
    ' Create a BatchBlock<Employee> that holds several Employee objects and
    ' then propagates them out as an array.
    Dim batchEmployees = New BatchBlock(Of Employee)(batchSize)

    ' Create an ActionBlock<Employee[]> object that adds multiple
    ' employee entries to the database.
    Dim insertEmployees = New ActionBlock(Of Employee())(Sub(a) Program.InsertEmployees(a, connectionString))

    ' Link the batch block to the action block.
    batchEmployees.LinkTo(insertEmployees)

    ' When the batch block completes, set the action block also to complete.
    batchEmployees.Completion.ContinueWith(Sub() insertEmployees.Complete())

    ' Post several random Employee objects to the batch block.
    PostRandomEmployees(batchEmployees, count)

    ' Set the batch block to the completed state and wait for 
    ' all insert operations to complete.
    batchEmployees.Complete()
    insertEmployees.Completion.Wait()
End Sub

Diese Methode ähnelt AddEmployees, mit der Ausnahme, dass sie auch die BatchBlock<T> Klasse verwendet, um mehrere Employee Objekte zu puffern, bevor sie diese Objekte an das ActionBlock<TInput> Objekt sendet. Da die BatchBlock<T> Klasse mehrere Elemente als Auflistung verteilt, wird das ActionBlock<TInput> Objekt geändert, um auf ein Array von Employee Objekten zu reagieren. Wie bei der AddEmployees-Methode ruft die AddEmployeesBatched-Methode die PostRandomEmployees-Methode auf, um mehrere Employee-Objekte zu posten; allerdings werden diese Objekte an das BatchBlock<T>-Objekt gepostet. Die AddEmployeesBatched Methode wartet auch, bis alle Einfügevorgänge abgeschlossen sind.

Verwenden von Buffered Join zum Lesen von Mitarbeiterdaten aus der Datenbank

Fügen Sie der Program Klasse die GetRandomEmployees Methode hinzu.

// Displays information about several random employees to the console.
static void GetRandomEmployees(string connectionString, int batchSize,
   int count)
{
   // Create a BatchedJoinBlock<Employee, Exception> object that holds
   // both employee and exception data.
   var selectEmployees = new BatchedJoinBlock<Employee, Exception>(batchSize);

   // Holds the total number of exceptions that occurred.
   int totalErrors = 0;

   // Create an action block that prints employee and error information
   // to the console.
   var printEmployees =
      new ActionBlock<Tuple<IList<Employee>, IList<Exception>>>(data =>
      {
         // Print information about the employees in this batch.
         Console.WriteLine("Received a batch...");
         foreach (Employee e in data.Item1)
         {
            Console.WriteLine($"Last={e.LastName} First={e.FirstName} ID={e.EmployeeID}");
         }

         // Print the error count for this batch.
         Console.WriteLine($"There were {data.Item2.Count} errors in this batch...");

         // Update total error count.
         totalErrors += data.Item2.Count;
      });

   // Link the batched join block to the action block.
   selectEmployees.LinkTo(printEmployees);

   // When the batched join block completes, set the action block also to complete.
   selectEmployees.Completion.ContinueWith(delegate { printEmployees.Complete(); });

   // Try to retrieve the ID for several random employees.
   Console.WriteLine("Selecting random entries from Employees table...");
   for (int i = 0; i < count; i++)
   {
      try
      {
         // Create a random employee.
         Employee e = Employee.Random();

         // Try to retrieve the ID for the employee from the database.
         e.EmployeeID = GetEmployeeID(e.LastName, e.FirstName, connectionString);

         // Post the Employee object to the Employee target of
         // the batched join block.
         selectEmployees.Target1.Post(e);
      }
      catch (NullReferenceException e)
      {
         // GetEmployeeID throws NullReferenceException when there is
         // no such employee with the given name. When this happens,
         // post the Exception object to the Exception target of
         // the batched join block.
         selectEmployees.Target2.Post(e);
      }
   }

   // Set the batched join block to the completed state and wait for
   // all retrieval operations to complete.
   selectEmployees.Complete();
   printEmployees.Completion.Wait();

   // Print the total error count.
   Console.WriteLine($"Finished. There were {totalErrors} total errors.");
}

' Displays information about several random employees to the console.
Private Shared Sub GetRandomEmployees(ByVal connectionString As String, ByVal batchSize As Integer, ByVal count As Integer)
    ' Create a BatchedJoinBlock<Employee, Exception> object that holds
    ' both employee and exception data.
    Dim selectEmployees = New BatchedJoinBlock(Of Employee, Exception)(batchSize)

    ' Holds the total number of exceptions that occurred.
    Dim totalErrors As Integer = 0

    ' Create an action block that prints employee and error information
    ' to the console.
    Dim printEmployees = New ActionBlock(Of Tuple(Of IList(Of Employee), IList(Of Exception)))(Sub(data)
                                                                                                   ' Print information about the employees in this batch.
                                                                                                   ' Print the error count for this batch.
                                                                                                   ' Update total error count.
                                                                                                   Console.WriteLine("Received a batch...")
                                                                                                   For Each e As Employee In data.Item1
                                                                                                       Console.WriteLine("Last={0} First={1} ID={2}", e.LastName, e.FirstName, e.EmployeeID)
                                                                                                   Next e
                                                                                                   Console.WriteLine("There were {0} errors in this batch...", data.Item2.Count)
                                                                                                   totalErrors += data.Item2.Count
                                                                                               End Sub)

    ' Link the batched join block to the action block.
    selectEmployees.LinkTo(printEmployees)

    ' When the batched join block completes, set the action block also to complete.
    selectEmployees.Completion.ContinueWith(Sub() printEmployees.Complete())

    ' Try to retrieve the ID for several random employees.
    Console.WriteLine("Selecting random entries from Employees table...")
    For i As Integer = 0 To count - 1
        Try
            ' Create a random employee.
            Dim e As Employee = Employee.Random()

            ' Try to retrieve the ID for the employee from the database.
            e.EmployeeID = GetEmployeeID(e.LastName, e.FirstName, connectionString)

            ' Post the Employee object to the Employee target of 
            ' the batched join block.
            selectEmployees.Target1.Post(e)
        Catch e As NullReferenceException
            ' GetEmployeeID throws NullReferenceException when there is 
            ' no such employee with the given name. When this happens,
            ' post the Exception object to the Exception target of
            ' the batched join block.
            selectEmployees.Target2.Post(e)
        End Try
    Next i

    ' Set the batched join block to the completed state and wait for 
    ' all retrieval operations to complete.
    selectEmployees.Complete()
    printEmployees.Completion.Wait()

    ' Print the total error count.
    Console.WriteLine("Finished. There were {0} total errors.", totalErrors)
End Sub

Diese Methode gibt Informationen über zufällige Mitarbeiter auf der Konsole aus. Es erstellt mehrere zufällige Employee Objekte und ruft die GetEmployeeID Methode auf, um den eindeutigen Bezeichner für jedes Objekt abzurufen. Da die GetEmployeeID Methode eine Ausnahme auslöst, wenn kein übereinstimmende Mitarbeiter mit den angegebenen Vor- und Nachnamen vorhanden ist, verwendet die GetRandomEmployees Methode die BatchedJoinBlock<T1,T2> Klasse, um Objekte für erfolgreiche Aufrufe und Employee Objekte für Aufrufe zu GetEmployeeID speichernSystem.Exception, die fehlschlagen. Das ActionBlock<TInput> Objekt in diesem Beispiel fungiert für ein Tuple<T1,T2> Objekt, das eine Liste von Employee Objekten und eine Liste von Exception Objekten enthält. Das BatchedJoinBlock<T1,T2> Objekt verteilt diese Daten, wenn die Summe der empfangenen Employee und Exception Objekte der Batchgröße entspricht.

Vollständiges Beispiel

Das folgende Beispiel zeigt den vollständigen Code. Die Main Methode vergleicht die Zeit, die zum Ausführen von Batch-Datenbankeinfügungen erforderlich ist, im Vergleich zur Zeit zum Ausführen von Nicht-Batch-Datenbankeinfügungen. Außerdem wird die Verwendung der gepufferten Verknüpfung zum Lesen von Mitarbeiterdaten aus der Datenbank und zum Melden von Fehlern veranschaulicht.

using System;
using System.Collections.Generic;
using System.Data.SqlClient;
using System.Diagnostics;
using System.IO;
using System.Threading.Tasks.Dataflow;

// Demonstrates how to use batched dataflow blocks to improve
// the performance of database operations.
namespace DataflowBatchDatabase
{
   class Program
   {
      // The number of employees to add to the database.
      // TODO: Change this value to experiment with different numbers of
      // employees to insert into the database.
      static readonly int insertCount = 256;

      // The size of a single batch of employees to add to the database.
      // TODO: Change this value to experiment with different batch sizes.
      static readonly int insertBatchSize = 96;

      // The source database file.
      // TODO: Change this value if Northwind.sdf is at a different location
      // on your computer.
      static readonly string sourceDatabase =
         @"C:\...\Northwind.sdf";

      // TODO: Change this value if you require a different temporary location.
      static readonly string scratchDatabase =
         @"C:\Temp\Northwind.sdf";

      // Describes an employee. Each property maps to a
      // column in the Employees table in the Northwind database.
      // For brevity, the Employee class does not contain
      // all columns from the Employees table.
      class Employee
      {
         public int EmployeeID { get; set; }
         public string LastName { get; set; }
         public string FirstName { get; set; }

         // A random number generator that helps tp generate
         // Employee property values.
         static Random rand = new Random(42);

         // Possible random first names.
         static readonly string[] firstNames = { "Tom", "Mike", "Ruth", "Bob", "John" };
         // Possible random last names.
         static readonly string[] lastNames = { "Jones", "Smith", "Johnson", "Walker" };

         // Creates an Employee object that contains random
         // property values.
         public static Employee Random()
         {
            return new Employee
            {
               EmployeeID = -1,
               LastName = lastNames[rand.Next() % lastNames.Length],
               FirstName = firstNames[rand.Next() % firstNames.Length]
            };
         }
      }

      // Adds new employee records to the database.
      static void InsertEmployees(Employee[] employees, string connectionString)
      {
         using (SqlConnection connection =
            new SqlConnection(connectionString))
         {
            try
            {
               // Create the SQL command.
               SqlCommand command = new SqlCommand(
                  "INSERT INTO Employees ([Last Name], [First Name])" +
                  "VALUES (@lastName, @firstName)",
                  connection);

               connection.Open();
               for (int i = 0; i < employees.Length; i++)
               {
                  // Set parameters.
                  command.Parameters.Clear();
                  command.Parameters.Add("@lastName", employees[i].LastName);
                  command.Parameters.Add("@firstName", employees[i].FirstName);

                  // Execute the command.
                  command.ExecuteNonQuery();
               }
            }
            finally
            {
               connection.Close();
            }
         }
      }

      // Retrieves the number of entries in the Employees table in
      // the Northwind database.
      static int GetEmployeeCount(string connectionString)
      {
         int result = 0;
         using (SqlConnection sqlConnection =
            new SqlConnection(connectionString))
         {
            SqlCommand sqlCommand = new SqlCommand(
               "SELECT COUNT(*) FROM Employees", sqlConnection);

            sqlConnection.Open();
            try
            {
               result = (int)sqlCommand.ExecuteScalar();
            }
            finally
            {
               sqlConnection.Close();
            }
         }
         return result;
      }

      // Retrieves the ID of the first employee that has the provided name.
      static int GetEmployeeID(string lastName, string firstName,
         string connectionString)
      {
         using (SqlConnection connection =
            new SqlConnection(connectionString))
         {
            SqlCommand command = new SqlCommand(
               string.Format(
                  "SELECT [Employee ID] FROM Employees " +
                  "WHERE [Last Name] = '{0}' AND [First Name] = '{1}'",
                  lastName, firstName),
               connection);

            connection.Open();
            try
            {
               return (int)command.ExecuteScalar();
            }
            finally
            {
               connection.Close();
            }
         }
      }

      // Posts random Employee data to the provided target block.
      static void PostRandomEmployees(ITargetBlock<Employee> target, int count)
      {
         Console.WriteLine($"Adding {count} entries to Employee table...");

         for (int i = 0; i < count; i++)
         {
            target.Post(Employee.Random());
         }
      }

      // Adds random employee data to the database by using dataflow.
      static void AddEmployees(string connectionString, int count)
      {
         // Create an ActionBlock<Employee> object that adds a single
         // employee entry to the database.
         var insertEmployee = new ActionBlock<Employee>(e =>
            InsertEmployees(new Employee[] { e }, connectionString));

         // Post several random Employee objects to the dataflow block.
         PostRandomEmployees(insertEmployee, count);

         // Set the dataflow block to the completed state and wait for
         // all insert operations to complete.
         insertEmployee.Complete();
         insertEmployee.Completion.Wait();
      }

      // Adds random employee data to the database by using dataflow.
      // This method is similar to AddEmployees except that it uses batching
      // to add multiple employees to the database at a time.
      static void AddEmployeesBatched(string connectionString, int batchSize,
         int count)
      {
         // Create a BatchBlock<Employee> that holds several Employee objects and
         // then propagates them out as an array.
         var batchEmployees = new BatchBlock<Employee>(batchSize);

         // Create an ActionBlock<Employee[]> object that adds multiple
         // employee entries to the database.
         var insertEmployees = new ActionBlock<Employee[]>(a =>
            InsertEmployees(a, connectionString));

         // Link the batch block to the action block.
         batchEmployees.LinkTo(insertEmployees);

         // When the batch block completes, set the action block also to complete.
         batchEmployees.Completion.ContinueWith(delegate { insertEmployees.Complete(); });

         // Post several random Employee objects to the batch block.
         PostRandomEmployees(batchEmployees, count);

         // Set the batch block to the completed state and wait for
         // all insert operations to complete.
         batchEmployees.Complete();
         insertEmployees.Completion.Wait();
      }

      // Displays information about several random employees to the console.
      static void GetRandomEmployees(string connectionString, int batchSize,
         int count)
      {
         // Create a BatchedJoinBlock<Employee, Exception> object that holds
         // both employee and exception data.
         var selectEmployees = new BatchedJoinBlock<Employee, Exception>(batchSize);

         // Holds the total number of exceptions that occurred.
         int totalErrors = 0;

         // Create an action block that prints employee and error information
         // to the console.
         var printEmployees =
            new ActionBlock<Tuple<IList<Employee>, IList<Exception>>>(data =>
            {
               // Print information about the employees in this batch.
               Console.WriteLine("Received a batch...");
               foreach (Employee e in data.Item1)
               {
                  Console.WriteLine($"Last={e.LastName} First={e.FirstName} ID={e.EmployeeID}");
               }

               // Print the error count for this batch.
               Console.WriteLine($"There were {data.Item2.Count} errors in this batch...");

               // Update total error count.
               totalErrors += data.Item2.Count;
            });

         // Link the batched join block to the action block.
         selectEmployees.LinkTo(printEmployees);

         // When the batched join block completes, set the action block also to complete.
         selectEmployees.Completion.ContinueWith(delegate { printEmployees.Complete(); });

         // Try to retrieve the ID for several random employees.
         Console.WriteLine("Selecting random entries from Employees table...");
         for (int i = 0; i < count; i++)
         {
            try
            {
               // Create a random employee.
               Employee e = Employee.Random();

               // Try to retrieve the ID for the employee from the database.
               e.EmployeeID = GetEmployeeID(e.LastName, e.FirstName, connectionString);

               // Post the Employee object to the Employee target of
               // the batched join block.
               selectEmployees.Target1.Post(e);
            }
            catch (NullReferenceException e)
            {
               // GetEmployeeID throws NullReferenceException when there is
               // no such employee with the given name. When this happens,
               // post the Exception object to the Exception target of
               // the batched join block.
               selectEmployees.Target2.Post(e);
            }
         }

         // Set the batched join block to the completed state and wait for
         // all retrieval operations to complete.
         selectEmployees.Complete();
         printEmployees.Completion.Wait();

         // Print the total error count.
         Console.WriteLine($"Finished. There were {totalErrors} total errors.");
      }

      static void Main(string[] args)
      {
         // Create a connection string for accessing the database.
         // The connection string refers to the temporary database location.
         string connectionString = "...";

         // Create a Stopwatch object to time database insert operations.
         Stopwatch stopwatch = new Stopwatch();

         // Start with a clean database file by copying the source database to
         // the temporary location.
         File.Copy(sourceDatabase, scratchDatabase, true);

         // Demonstrate multiple insert operations without batching.
         Console.WriteLine("Demonstrating non-batched database insert operations...");
         Console.WriteLine($"Original size of Employee table: {GetEmployeeCount(connectionString)}.");
         stopwatch.Start();
         AddEmployees(connectionString, insertCount);
         stopwatch.Stop();
         Console.WriteLine("New size of Employee table: {0}; elapsed insert time: {1} ms.",
            GetEmployeeCount(connectionString), stopwatch.ElapsedMilliseconds);

         Console.WriteLine();

         // Start again with a clean database file.
         File.Copy(sourceDatabase, scratchDatabase, true);

         // Demonstrate multiple insert operations, this time with batching.
         Console.WriteLine("Demonstrating batched database insert operations...");
         Console.WriteLine($"Original size of Employee table: {GetEmployeeCount(connectionString)}.");
         stopwatch.Restart();
         AddEmployeesBatched(connectionString, insertBatchSize, insertCount);
         stopwatch.Stop();
         Console.WriteLine("New size of Employee table: {0}; elapsed insert time: {1} ms.",
            GetEmployeeCount(connectionString), stopwatch.ElapsedMilliseconds);

         Console.WriteLine();

         // Start again with a clean database file.
         File.Copy(sourceDatabase, scratchDatabase, true);

         // Demonstrate multiple retrieval operations with error reporting.
         Console.WriteLine("Demonstrating batched join database select operations...");
         // Add a small number of employees to the database.
         AddEmployeesBatched(connectionString, insertBatchSize, 16);
         // Query for random employees.
         GetRandomEmployees(connectionString, insertBatchSize, 10);
      }
   }
}
/* Sample output:
Demonstrating non-batched database insert operations...
Original size of Employee table: 15.
Adding 256 entries to Employee table...
New size of Employee table: 271; elapsed insert time: 11035 ms.

Demonstrating batched database insert operations...
Original size of Employee table: 15.
Adding 256 entries to Employee table...
New size of Employee table: 271; elapsed insert time: 197 ms.

Demonstrating batched join database insert operations...
Adding 16 entries to Employee table...
Selecting items from Employee table...
Received a batch...
Last=Jones First=Tom ID=21
Last=Jones First=John ID=24
Last=Smith First=Tom ID=26
Last=Jones First=Tom ID=21
There were 4 errors in this batch...
Received a batch...
Last=Smith First=Tom ID=26
Last=Jones First=Mike ID=28
There were 0 errors in this batch...
Finished. There were 4 total errors.
*/

Imports System.Collections.Generic
Imports System.Data.SqlClient
Imports System.Data.SqlServerCe
Imports System.Diagnostics
Imports System.IO
Imports System.Threading.Tasks.Dataflow


' Demonstrates how to use batched dataflow blocks to improve
' the performance of database operations.
Namespace DataflowBatchDatabase
    Friend Class Program
        ' The number of employees to add to the database.
        ' TODO: Change this value to experiment with different numbers of 
        ' employees to insert into the database.
        Private Shared ReadOnly insertCount As Integer = 256

        ' The size of a single batch of employees to add to the database.
        ' TODO: Change this value to experiment with different batch sizes.
        Private Shared ReadOnly insertBatchSize As Integer = 96

        ' The source database file.
        ' TODO: Change this value if Northwind.sdf is at a different location
        ' on your computer.
        Private Shared ReadOnly sourceDatabase As String = "C:\Program Files\Microsoft SQL Server Compact Edition\v3.5\Samples\Northwind.sdf"

        ' TODO: Change this value if you require a different temporary location.
        Private Shared ReadOnly scratchDatabase As String = "C:\Temp\Northwind.sdf"

        ' Describes an employee. Each property maps to a 
        ' column in the Employees table in the Northwind database.
        ' For brevity, the Employee class does not contain
        ' all columns from the Employees table.
        Private Class Employee
            Public Property EmployeeID() As Integer
            Public Property LastName() As String
            Public Property FirstName() As String

            ' A random number generator that helps tp generate
            ' Employee property values.
            Private Shared rand As New Random(42)

            ' Possible random first names.
            Private Shared ReadOnly firstNames() As String = {"Tom", "Mike", "Ruth", "Bob", "John"}
            ' Possible random last names.
            Private Shared ReadOnly lastNames() As String = {"Jones", "Smith", "Johnson", "Walker"}

            ' Creates an Employee object that contains random 
            ' property values.
            Public Shared Function Random() As Employee
                Return New Employee With {.EmployeeID = -1, .LastName = lastNames(rand.Next() Mod lastNames.Length), .FirstName = firstNames(rand.Next() Mod firstNames.Length)}
            End Function
        End Class

        ' Adds new employee records to the database.
        Private Shared Sub InsertEmployees(ByVal employees() As Employee, ByVal connectionString As String)
            Using connection As New SqlConnection(connectionString)
                Try
                    ' Create the SQL command.
                    Dim command As New SqlCommand("INSERT INTO Employees ([Last Name], [First Name])" & "VALUES (@lastName, @firstName)", connection)

                    connection.Open()
                    For i As Integer = 0 To employees.Length - 1
                        ' Set parameters.
                        command.Parameters.Clear()
                        command.Parameters.Add("@lastName", employees(i).LastName)
                        command.Parameters.Add("@firstName", employees(i).FirstName)

                        ' Execute the command.
                        command.ExecuteNonQuery()
                    Next i
                Finally
                    connection.Close()
                End Try
            End Using
        End Sub

        ' Retrieves the number of entries in the Employees table in 
        ' the Northwind database.
        Private Shared Function GetEmployeeCount(ByVal connectionString As String) As Integer
            Dim result As Integer = 0
            Using sqlConnection As New SqlConnection(connectionString)
                Dim sqlCommand As New SqlCommand("SELECT COUNT(*) FROM Employees", sqlConnection)

                sqlConnection.Open()
                Try
                    result = CInt(Fix(sqlCommand.ExecuteScalar()))
                Finally
                    sqlConnection.Close()
                End Try
            End Using
            Return result
        End Function

        ' Retrieves the ID of the first employee that has the provided name.
        Private Shared Function GetEmployeeID(ByVal lastName As String, ByVal firstName As String, ByVal connectionString As String) As Integer
            Using connection As New SqlConnection(connectionString)
                Dim command As New SqlCommand(String.Format("SELECT [Employee ID] FROM Employees " & "WHERE [Last Name] = '{0}' AND [First Name] = '{1}'", lastName, firstName), connection)

                connection.Open()
                Try
                    Return CInt(Fix(command.ExecuteScalar()))
                Finally
                    connection.Close()
                End Try
            End Using
        End Function

        ' Posts random Employee data to the provided target block.
        Private Shared Sub PostRandomEmployees(ByVal target As ITargetBlock(Of Employee), ByVal count As Integer)
            Console.WriteLine("Adding {0} entries to Employee table...", count)

            For i As Integer = 0 To count - 1
                target.Post(Employee.Random())
            Next i
        End Sub

        ' Adds random employee data to the database by using dataflow.
        Private Shared Sub AddEmployees(ByVal connectionString As String, ByVal count As Integer)
            ' Create an ActionBlock<Employee> object that adds a single
            ' employee entry to the database.
            Dim insertEmployee = New ActionBlock(Of Employee)(Sub(e) InsertEmployees(New Employee() {e}, connectionString))

            ' Post several random Employee objects to the dataflow block.
            PostRandomEmployees(insertEmployee, count)

            ' Set the dataflow block to the completed state and wait for 
            ' all insert operations to complete.
            insertEmployee.Complete()
            insertEmployee.Completion.Wait()
        End Sub

        ' Adds random employee data to the database by using dataflow.
        ' This method is similar to AddEmployees except that it uses batching
        ' to add multiple employees to the database at a time.
        Private Shared Sub AddEmployeesBatched(ByVal connectionString As String, ByVal batchSize As Integer, ByVal count As Integer)
            ' Create a BatchBlock<Employee> that holds several Employee objects and
            ' then propagates them out as an array.
            Dim batchEmployees = New BatchBlock(Of Employee)(batchSize)

            ' Create an ActionBlock<Employee[]> object that adds multiple
            ' employee entries to the database.
            Dim insertEmployees = New ActionBlock(Of Employee())(Sub(a) Program.InsertEmployees(a, connectionString))

            ' Link the batch block to the action block.
            batchEmployees.LinkTo(insertEmployees)

            ' When the batch block completes, set the action block also to complete.
            batchEmployees.Completion.ContinueWith(Sub() insertEmployees.Complete())

            ' Post several random Employee objects to the batch block.
            PostRandomEmployees(batchEmployees, count)

            ' Set the batch block to the completed state and wait for 
            ' all insert operations to complete.
            batchEmployees.Complete()
            insertEmployees.Completion.Wait()
        End Sub

        ' Displays information about several random employees to the console.
        Private Shared Sub GetRandomEmployees(ByVal connectionString As String, ByVal batchSize As Integer, ByVal count As Integer)
            ' Create a BatchedJoinBlock<Employee, Exception> object that holds
            ' both employee and exception data.
            Dim selectEmployees = New BatchedJoinBlock(Of Employee, Exception)(batchSize)

            ' Holds the total number of exceptions that occurred.
            Dim totalErrors As Integer = 0

            ' Create an action block that prints employee and error information
            ' to the console.
            Dim printEmployees = New ActionBlock(Of Tuple(Of IList(Of Employee), IList(Of Exception)))(Sub(data)
                                                                                                           ' Print information about the employees in this batch.
                                                                                                           ' Print the error count for this batch.
                                                                                                           ' Update total error count.
                                                                                                           Console.WriteLine("Received a batch...")
                                                                                                           For Each e As Employee In data.Item1
                                                                                                               Console.WriteLine("Last={0} First={1} ID={2}", e.LastName, e.FirstName, e.EmployeeID)
                                                                                                           Next e
                                                                                                           Console.WriteLine("There were {0} errors in this batch...", data.Item2.Count)
                                                                                                           totalErrors += data.Item2.Count
                                                                                                       End Sub)

            ' Link the batched join block to the action block.
            selectEmployees.LinkTo(printEmployees)

            ' When the batched join block completes, set the action block also to complete.
            selectEmployees.Completion.ContinueWith(Sub() printEmployees.Complete())

            ' Try to retrieve the ID for several random employees.
            Console.WriteLine("Selecting random entries from Employees table...")
            For i As Integer = 0 To count - 1
                Try
                    ' Create a random employee.
                    Dim e As Employee = Employee.Random()

                    ' Try to retrieve the ID for the employee from the database.
                    e.EmployeeID = GetEmployeeID(e.LastName, e.FirstName, connectionString)

                    ' Post the Employee object to the Employee target of 
                    ' the batched join block.
                    selectEmployees.Target1.Post(e)
                Catch e As NullReferenceException
                    ' GetEmployeeID throws NullReferenceException when there is 
                    ' no such employee with the given name. When this happens,
                    ' post the Exception object to the Exception target of
                    ' the batched join block.
                    selectEmployees.Target2.Post(e)
                End Try
            Next i

            ' Set the batched join block to the completed state and wait for 
            ' all retrieval operations to complete.
            selectEmployees.Complete()
            printEmployees.Completion.Wait()

            ' Print the total error count.
            Console.WriteLine("Finished. There were {0} total errors.", totalErrors)
        End Sub

        Shared Sub Main(ByVal args() As String)
            ' Create a connection string for accessing the database.
            ' The connection string refers to the temporary database location.
            Dim connectionString As String = String.Format("Data Source={0}", scratchDatabase)

            ' Create a Stopwatch object to time database insert operations.
            Dim stopwatch As New Stopwatch()

            ' Start with a clean database file by copying the source database to 
            ' the temporary location.
            File.Copy(sourceDatabase, scratchDatabase, True)

            ' Demonstrate multiple insert operations without batching.
            Console.WriteLine("Demonstrating non-batched database insert operations...")
            Console.WriteLine("Original size of Employee table: {0}.", GetEmployeeCount(connectionString))
            stopwatch.Start()
            AddEmployees(connectionString, insertCount)
            stopwatch.Stop()
            Console.WriteLine("New size of Employee table: {0}; elapsed insert time: {1} ms.", GetEmployeeCount(connectionString), stopwatch.ElapsedMilliseconds)

            Console.WriteLine()

            ' Start again with a clean database file.
            File.Copy(sourceDatabase, scratchDatabase, True)

            ' Demonstrate multiple insert operations, this time with batching.
            Console.WriteLine("Demonstrating batched database insert operations...")
            Console.WriteLine("Original size of Employee table: {0}.", GetEmployeeCount(connectionString))
            stopwatch.Restart()
            AddEmployeesBatched(connectionString, insertBatchSize, insertCount)
            stopwatch.Stop()
            Console.WriteLine("New size of Employee table: {0}; elapsed insert time: {1} ms.", GetEmployeeCount(connectionString), stopwatch.ElapsedMilliseconds)

            Console.WriteLine()

            ' Start again with a clean database file.
            File.Copy(sourceDatabase, scratchDatabase, True)

            ' Demonstrate multiple retrieval operations with error reporting.
            Console.WriteLine("Demonstrating batched join database select operations...")
            ' Add a small number of employees to the database.
            AddEmployeesBatched(connectionString, insertBatchSize, 16)
            ' Query for random employees.
            GetRandomEmployees(connectionString, insertBatchSize, 10)
        End Sub
    End Class
End Namespace
' Sample output:
'Demonstrating non-batched database insert operations...
'Original size of Employee table: 15.
'Adding 256 entries to Employee table...
'New size of Employee table: 271; elapsed insert time: 11035 ms.
'
'Demonstrating batched database insert operations...
'Original size of Employee table: 15.
'Adding 256 entries to Employee table...
'New size of Employee table: 271; elapsed insert time: 197 ms.
'
'Demonstrating batched join database insert operations...
'Adding 16 entries to Employee table...
'Selecting items from Employee table...
'Received a batch...
'Last=Jones First=Tom ID=21
'Last=Jones First=John ID=24
'Last=Smith First=Tom ID=26
'Last=Jones First=Tom ID=21
'There were 4 errors in this batch...
'Received a batch...
'Last=Smith First=Tom ID=26
'Last=Jones First=Mike ID=28
'There were 0 errors in this batch...
'Finished. There were 4 total errors.
'

Siehe auch

  • Last updated on