SqlBulkCopyColumnMappingCollection.Clear Metoda

Definice

Obor názvů:

System.Data.SqlClient

Sestavení:

System.Data.dll

Vymaže obsah kolekce.

public:
 void Clear();

public void Clear ();

override this.Clear : unit -> unit

Public Sub Clear ()

Příklady

Následující příklad provádí dvě operace hromadného kopírování. První operace zkopíruje informace o záhlaví prodejní objednávky a druhá zkopíruje podrobnosti prodejní objednávky. I když to v tomto příkladu není nezbytně nutné (protože pořadí řad zdrojového a cílového sloupce se shodují), tento příklad definuje mapování sloupců pro každou operaci hromadného kopírování. Metoda Clear musí být použita po prvním hromadném kopírování a před definováním mapování sloupců další hromadné kopírování.

Důležité

Tato ukázka se nespustí, pokud jste nevytvořili pracovní tabulky, jak je popsáno v příkladu hromadného kopírování. Tento kód je k dispozici k předvedení syntaxe pouze pro použití SqlBulkCopy . Pokud jsou zdrojová a cílová tabulka ve stejné SQL Server instanci, je jednodušší a rychlejší zkopírovat data pomocí příkazu Jazyka Transact-SQLINSERT ... SELECT.

using System.Data.SqlClient;

class Program
{
    static void Main()
    {
        string connectionString = GetConnectionString();
        // Open a connection to the AdventureWorks database.
        using (SqlConnection connection =
                   new SqlConnection(connectionString))
        {
            connection.Open();

            // Empty the destination tables.
            SqlCommand deleteHeader = new SqlCommand(
                "DELETE FROM dbo.BulkCopyDemoOrderHeader;",
                connection);
            deleteHeader.ExecuteNonQuery();
            SqlCommand deleteDetail = new SqlCommand(
                "DELETE FROM dbo.BulkCopyDemoOrderDetail;",
                connection);
            deleteDetail.ExecuteNonQuery();

            // Perform an initial count on the destination
            //  table with matching columns.
            SqlCommand countRowHeader = new SqlCommand(
                "SELECT COUNT(*) FROM dbo.BulkCopyDemoOrderHeader;",
                connection);
            long countStartHeader = System.Convert.ToInt32(
                countRowHeader.ExecuteScalar());
            Console.WriteLine(
                "Starting row count for Header table = {0}",
                countStartHeader);

            // Perform an initial count on the destination
            // table with different column positions.
            SqlCommand countRowDetail = new SqlCommand(
                "SELECT COUNT(*) FROM dbo.BulkCopyDemoOrderDetail;",
                connection);
            long countStartDetail = System.Convert.ToInt32(
                countRowDetail.ExecuteScalar());
            Console.WriteLine(
                "Starting row count for Detail table = {0}",
                countStartDetail);

            // Get data from the source table as a SqlDataReader.
            // The Sales.SalesOrderHeader and Sales.SalesOrderDetail
            // tables are quite large and could easily cause a timeout
            // if all data from the tables is added to the destination.
            // To keep the example simple and quick, a parameter is
            // used to select only orders for a particular account
            // as the source for the bulk insert.
            SqlCommand headerData = new SqlCommand(
                "SELECT [SalesOrderID], [OrderDate], " +
                "[AccountNumber] FROM [Sales].[SalesOrderHeader] " +
                "WHERE [AccountNumber] = @accountNumber;",
                connection);
            SqlParameter parameterAccount = new SqlParameter();
            parameterAccount.ParameterName = "@accountNumber";
            parameterAccount.SqlDbType = SqlDbType.NVarChar;
            parameterAccount.Direction = ParameterDirection.Input;
            parameterAccount.Value = "10-4020-000034";
            headerData.Parameters.Add(parameterAccount);
            SqlDataReader readerHeader = headerData.ExecuteReader();

            // Get the Detail data in a separate connection.
            using (SqlConnection connection2 = new SqlConnection(connectionString))
            {
                connection2.Open();
                SqlCommand sourceDetailData = new SqlCommand(
                    "SELECT [Sales].[SalesOrderDetail].[SalesOrderID], [SalesOrderDetailID], " +
                    "[OrderQty], [ProductID], [UnitPrice] FROM [Sales].[SalesOrderDetail] " +
                    "INNER JOIN [Sales].[SalesOrderHeader] ON [Sales].[SalesOrderDetail]." +
                    "[SalesOrderID] = [Sales].[SalesOrderHeader].[SalesOrderID] " +
                    "WHERE [AccountNumber] = @accountNumber;", connection2);

                SqlParameter accountDetail = new SqlParameter();
                accountDetail.ParameterName = "@accountNumber";
                accountDetail.SqlDbType = SqlDbType.NVarChar;
                accountDetail.Direction = ParameterDirection.Input;
                accountDetail.Value = "10-4020-000034";
                sourceDetailData.Parameters.Add(accountDetail);
                SqlDataReader readerDetail = sourceDetailData.ExecuteReader();

                // Create the SqlBulkCopy object.
                using (SqlBulkCopy bulkCopy =
                           new SqlBulkCopy(connectionString))
                {
                    bulkCopy.DestinationTableName =
                        "dbo.BulkCopyDemoOrderHeader";

                    // Guarantee that columns are mapped correctly by
                    // defining the column mappings for the order.
                    bulkCopy.ColumnMappings.Add("SalesOrderID", "SalesOrderID");
                    bulkCopy.ColumnMappings.Add("OrderDate", "OrderDate");
                    bulkCopy.ColumnMappings.Add("AccountNumber", "AccountNumber");

                    // Write readerHeader to the destination.
                    try
                    {
                        bulkCopy.WriteToServer(readerHeader);
                    }
                    catch (Exception ex)
                    {
                        Console.WriteLine(ex.Message);
                    }
                    finally
                    {
                        readerHeader.Close();
                    }

                    // Set up the order details destination.
                    bulkCopy.DestinationTableName ="dbo.BulkCopyDemoOrderDetail";

                    // Clear the ColumnMappingCollection.
                    bulkCopy.ColumnMappings.Clear();

                    // Add order detail column mappings.
                    bulkCopy.ColumnMappings.Add("SalesOrderID", "SalesOrderID");
                    bulkCopy.ColumnMappings.Add("SalesOrderDetailID", "SalesOrderDetailID");
                    bulkCopy.ColumnMappings.Add("OrderQty", "OrderQty");
                    bulkCopy.ColumnMappings.Add("ProductID", "ProductID");
                    bulkCopy.ColumnMappings.Add("UnitPrice", "UnitPrice");

                    // Write readerDetail to the destination.
                    try
                    {
                        bulkCopy.WriteToServer(readerDetail);
                    }
                    catch (Exception ex)
                    {
                        Console.WriteLine(ex.Message);
                    }
                    finally
                    {
                        readerDetail.Close();
                    }
                }

                // Perform a final count on the destination
                // tables to see how many rows were added.
                long countEndHeader = System.Convert.ToInt32(
                    countRowHeader.ExecuteScalar());
                Console.WriteLine("{0} rows were added to the Header table.",
                    countEndHeader - countStartHeader);
                long countEndDetail = System.Convert.ToInt32(
                    countRowDetail.ExecuteScalar());
                Console.WriteLine("{0} rows were added to the Detail table.",
                    countEndDetail - countStartDetail);
                Console.WriteLine("Press Enter to finish.");
                Console.ReadLine();
            }
        }
    }

    private static string GetConnectionString()
        // To avoid storing the connection string in your code,
        // you can retrieve it from a configuration file.
    {
        return "Data Source=(local); " +
            " Integrated Security=true;" +
            "Initial Catalog=AdventureWorks;";
    }
}

Imports System.Data.SqlClient

Module Module1
    Sub Main()
        Dim connectionString As String = GetConnectionString()

        ' Open a connection to the AdventureWorks database.
        Using connection As SqlConnection = New SqlConnection(connectionString)
            connection.Open()

            ' Empty the destination tables.
            Dim deleteHeader As New SqlCommand( _
              "DELETE FROM dbo.BulkCopyDemoOrderHeader;", connection)
            deleteHeader.ExecuteNonQuery()
            deleteHeader.Dispose()
            Dim deleteDetail As New SqlCommand( _
              "DELETE FROM dbo.BulkCopyDemoOrderDetail;", connection)
            deleteDetail.ExecuteNonQuery()

            ' Perform an initial count on the destination table 
            ' with matching columns.
            Dim countRowHeader As New SqlCommand( _
               "SELECT COUNT(*) FROM dbo.BulkCopyDemoOrderHeader;", _
                connection)
            Dim countStartHeader As Long = System.Convert.ToInt32( _
             countRowHeader.ExecuteScalar())
            Console.WriteLine("Starting row count for Header table = {0}", _
             countStartHeader)

            ' Perform an initial count on the destination table 
            ' with different column positions.
            Dim countRowDetail As New SqlCommand( _
                "SELECT COUNT(*) FROM dbo.BulkCopyDemoOrderDetail;", _
                connection)
            Dim countStartDetail As Long = System.Convert.ToInt32( _
                countRowDetail.ExecuteScalar())
            Console.WriteLine("Starting row count for Detail table = " & _
               countStartDetail)

            ' Get data from the source table as a SqlDataReader.
            ' The Sales.SalesOrderHeader and Sales.SalesOrderDetail
            ' tables are quite large and could easily cause a timeout
            ' if all data from the tables is added to the destination.
            ' To keep the example simple and quick, a parameter is 
            ' used to select only orders for a particular account as
            ' the source for the bulk insert.
            Dim headerData As SqlCommand = New SqlCommand( _
             "SELECT [SalesOrderID], [OrderDate], " & _
             "[AccountNumber] FROM [Sales].[SalesOrderHeader] " & _
             "WHERE [AccountNumber] = @accountNumber;", _
             connection)

            Dim parameterAccount As SqlParameter = New SqlParameter()
            parameterAccount.ParameterName = "@accountNumber"
            parameterAccount.SqlDbType = SqlDbType.NVarChar
            parameterAccount.Direction = ParameterDirection.Input
            parameterAccount.Value = "10-4020-000034"
            headerData.Parameters.Add(parameterAccount)

            Dim readerHeader As SqlDataReader = _
             headerData.ExecuteReader()

            ' Get the Detail data in a separate connection.
            Using connection2 As SqlConnection = New SqlConnection(connectionString)
                connection2.Open()

                Dim sourceDetailData As SqlCommand = New SqlCommand( _
                 "SELECT [Sales].[SalesOrderDetail].[SalesOrderID], " & _
                 "[SalesOrderDetailID], [OrderQty], [ProductID], [UnitPrice] " & _
                 "FROM [Sales].[SalesOrderDetail] INNER JOIN " & _
                 "[Sales].[SalesOrderHeader] " & _
                 "ON [Sales].[SalesOrderDetail].[SalesOrderID] = " & _
                 "[Sales].[SalesOrderHeader].[SalesOrderID] " & _
                 "WHERE [AccountNumber] = @accountNumber;", connection2)

                Dim accountDetail As SqlParameter = New SqlParameter()
                accountDetail.ParameterName = "@accountNumber"
                accountDetail.SqlDbType = SqlDbType.NVarChar
                accountDetail.Direction = ParameterDirection.Input
                accountDetail.Value = "10-4020-000034"
                sourceDetailData.Parameters.Add( _
                 accountDetail)

                Dim readerDetail As SqlDataReader = _
                 sourceDetailData.ExecuteReader()

                ' Create the SqlBulkCopy object.
                Using bulkCopy As SqlBulkCopy = _
                  New SqlBulkCopy(connectionString)
                    bulkCopy.DestinationTableName = "dbo.BulkCopyDemoOrderHeader"

                    ' Guarantee that columns are mapped correctly by
                    ' defining the column mappings for the order.
                    bulkCopy.ColumnMappings.Add("SalesOrderID", "SalesOrderID")
                    bulkCopy.ColumnMappings.Add("OrderDate", "OrderDate")
                    bulkCopy.ColumnMappings.Add("AccountNumber", "AccountNumber")
 
                   ' Write readerHeader to the destination.
                    Try
                        bulkCopy.WriteToServer(readerHeader)
                    Catch ex As Exception
                        Console.WriteLine(ex.Message)
                    Finally
                        readerHeader.Close()
                    End Try

                    ' Set up the order details destination.
                    bulkCopy.DestinationTableName = "dbo.BulkCopyDemoOrderDetail"

                    ' Clear the ColumnMappingCollection.
                    bulkCopy.ColumnMappings.Clear()

                    ' Add order detail column mappings.
                    bulkCopy.ColumnMappings.Add("SalesOrderID", "SalesOrderID")
                    bulkCopy.ColumnMappings.Add("SalesOrderDetailID", "SalesOrderDetailID")
                    bulkCopy.ColumnMappings.Add("OrderQty", "OrderQty")
                    bulkCopy.ColumnMappings.Add("ProductID", "ProductID")
                    bulkCopy.ColumnMappings.Add("UnitPrice", "UnitPrice")

                    ' Write readerDetail to the destination.
                    Try
                        bulkCopy.WriteToServer(readerDetail)
                    Catch ex As Exception
                        Console.WriteLine(ex.Message)
                    Finally
                        readerDetail.Close()
                    End Try
                End Using

                ' Perform a final count on the destination tables
                ' to see how many rows were added.
                Dim countEndHeader As Long = System.Convert.ToInt32( _
                  countRowHeader.ExecuteScalar())
                Console.WriteLine("{0} rows were added to the Header table.", _
                  countEndHeader - countStartHeader)
                Dim countEndDetail As Long = System.Convert.ToInt32( _
                   countRowDetail.ExecuteScalar())
                Console.WriteLine("{0} rows were added to the Detail table.", _
                    countEndDetail - countStartDetail)

                Console.WriteLine("Press Enter to finish.")
                Console.ReadLine()
            End Using
        End Using
    End Sub

    Private Function GetConnectionString() As String
        ' To avoid storing the connection string in your code, 
        ' you can retrieve it from a configuration file. 
        Return "Data Source=(local);" & _
            "Integrated Security=true;" & _
            "Initial Catalog=AdventureWorks;"
    End Function
End Module

Poznámky

Metoda se Clear nejčastěji používá při použití jedné SqlBulkCopy instance ke zpracování více než jedné operace hromadného kopírování. Pokud vytvoříte mapování sloupců pro jednu operaci hromadného kopírování, musíte vymazat SqlBulkCopyColumnMappingCollection následující metodu WriteToServer a před zpracováním další hromadné kopie.

Provedení několika hromadných kopií pomocí stejné SqlBulkCopy instance bude obvykle efektivnější z hlediska výkonu než použití samostatné SqlBulkCopy pro každou operaci.

Viz také

• Operace hromadného kopírování na SQL Serveru
• Přehled ADO.NET