Optimize プロパティの例 (VJ++)

この例では、Field オブジェクトのダイナミック Optimize プロパティの機能を示します。Pubs データベース内の Authors テーブルの zip フィールドには、インデックスが作成されていません。zip フィールドの Optimize プロパティを True に設定すると、ADO によってインデックスが作成され、Find メソッドのパフォーマンスが向上します。

import com.ms.wfc.data.*;
import java.io.* ;

public class OptimizeX
{
    // The main entry point for the application.

    public static void main (String[] args)
    {
        OptimizeX();
        System.exit(0);
    }

    // OptimizeX function

    static void OptimizeX()
    {

        // Define ADO Objects.
        Recordset rstAuthors = null;

        // Declarations.
        BufferedReader in = 
            new BufferedReader (new InputStreamReader(System.in));
        String strCnn = "DSN=Pubs;Provider=MSDASQL;uid=sa;pwd=;";

        try
        {
            rstAuthors = new Recordset();
            rstAuthors.setCursorLocation(AdoEnums.CursorLocation.CLIENT);
            // Enable index creation.
            rstAuthors.open("SELECT * FROM Authors",
                    strCnn,
                    AdoEnums.CursorType.STATIC,
                    AdoEnums.LockType.READONLY,
                    AdoEnums.CommandType.TEXT);
            rstAuthors.getField("zip").getProperties().
                getItem("Optimize").setBoolean(true); // Create the index.
            rstAuthors.find("zip = '94595'");    // Find Akiko Yokomoto.
            System.out.println(rstAuthors.getField("au_fname").getString() + 
                " " + rstAuthors.getField("au_lname").getString() + " " + 
                rstAuthors.getField("address").getString() + " " + 
                rstAuthors.getField("city").getString() + " " + 
                rstAuthors.getField("state").getString() + " ");
            rstAuthors.getField("zip").getProperties().
                getItem("Optimize").setBoolean(false); // Delete the index.

            // Cleanup objects before exit.
            rstAuthors.close();
            System.out.println("\nPress <Enter> to continue..");
            in.readLine();
        }
        catch( AdoException ae )
        {
            // Notify user of any errors that result from ADO.

            // As passing a Recordset, check for null pointer first.
            if (rstAuthors != null)
            {
                PrintProviderError(rstAuthors.getActiveConnection());
            }
            else
            {
                System.out.println("Exception: " + ae.getMessage());
            }
        }

        // System read requires this catch.
        catch( java.io.IOException je)
        {
            PrintIOError(je);
        }
    }

    // PrintProviderError Function

    static void PrintProviderError( Connection Cnn1 )
    {
        // Print Provider errors from Connection object.
        // ErrItem is an item object in the Connection’s Errors collection.
        com.ms.wfc.data.Error  ErrItem = null;
        long nCount = 0;
        int  i      = 0;

        nCount = Cnn1.getErrors().getCount();

        // If there are any errors in the collection, print them.
        if( nCount > 0);
        {
            // Collection ranges from 0 to nCount - 1
            for (i = 0; i< nCount; i++)
            {
                ErrItem = Cnn1.getErrors().getItem(i);
                System.out.println("\t Error number: " + ErrItem.getNumber()
                    + "\t" + ErrItem.getDescription() );
            }
        }

    }

    // PrintIOError Function

    static void PrintIOError( java.io.IOException je)
    {
        System.out.println("Error \n");
        System.out.println("\tSource = " + je.getClass() + "\n");
        System.out.println("\tDescription = " + je.getMessage() + "\n");
    }
}