SqlBulkCopyColumnMappingCollection.Clear Metodo

public:
 void Clear();

public void Clear ();

override this.Clear : unit -> unit

Public Sub Clear ()

Esempio

Nell'esempio seguente vengono eseguite due operazioni di copia bulk. La prima operazione copia le informazioni sull'intestazione dell'ordine di vendita e la seconda copia i dettagli dell'ordine di vendita. Anche se non è strettamente necessario in questo esempio (perché le posizioni ordinali delle colonne di origine e di destinazione corrispondono), l'esempio definisce i mapping di colonne per ogni operazione di copia bulk. Il Clear metodo deve essere usato dopo l'esecuzione della prima copia bulk e prima che vengano definiti i mapping delle colonne della copia bulk successiva.

using Microsoft.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;";
    }
}

Commenti

Il Clear metodo viene usato più comunemente quando si usa una singola SqlBulkCopy istanza per elaborare più operazioni di copia bulk. Se si creano mapping di colonne per un'operazione di copia bulk, è necessario cancellare il SqlBulkCopyColumnMappingCollection valore dopo il WriteToServer metodo e prima di elaborare la copia bulk successiva.

L'esecuzione di diverse copie bulk usando la stessa SqlBulkCopy istanza sarà in genere più efficiente da un punto di vista delle prestazioni rispetto all'uso di un'operazione separata SqlBulkCopy per ogni operazione.

Si applica a