SqlBulkCopyColumnMappingCollection.Clear Method

Definition

Namespace:

System.Data.SqlClient

Assembly:

System.Data.dll

Clears the contents of the collection.

public:
 void Clear();

public void Clear ();

override this.Clear : unit -> unit

Public Sub Clear ()

Examples

The following example performs two bulk copy operations. The first operation copies sales order header information, and the second copies sales order details. Although not strictly necessary in this example (because the ordinal positions of the source and destination columns do match), the example defines column mappings for each bulk copy operation. The Clear method must be used after the first bulk copy is performed and before the next bulk copy's column mappings are defined.

Important

This sample will not run unless you have created the work tables as described in Bulk Copy Example Setup. This code is provided to demonstrate the syntax for using SqlBulkCopy only. If the source and destination tables are in the same SQL Server instance, it is easier and faster to use a Transact-SQL INSERT ... SELECT statement to copy the data.

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

Remarks

The Clear method is most commonly used when you use a single SqlBulkCopy instance to process more than one bulk copy operation. If you create column mappings for one bulk copy operation, you must clear the SqlBulkCopyColumnMappingCollection after the WriteToServer method and before processing the next bulk copy.

Performing several bulk copies using the same SqlBulkCopy instance will usually be more efficient from a performance point of view than using a separate SqlBulkCopy for each operation.

See also

• Bulk Copy Operations in SQL Server
• ADO.NET Overview