openconglomeratescratchspace.java

derby database source code.good for you.

/*

   Derby - Class org.apache.derby.impl.store.access.conglomerate.OpenConglomerateScratchSpace

   Copyright 2000, 2004 The Apache Software Foundation or its licensors, as applicable.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.

 */

package org.apache.derby.impl.store.access.conglomerate;

import org.apache.derby.iapi.error.StandardException; 

import org.apache.derby.iapi.store.access.DynamicCompiledOpenConglomInfo;
import org.apache.derby.iapi.store.access.RowUtil;

import org.apache.derby.iapi.types.DataValueDescriptor;

import org.apache.derby.iapi.services.io.FormatableBitSet;
import org.apache.derby.iapi.services.loader.InstanceGetter;

/**

A utility class to store and use temporary scratch space associated with
a conglomerate.

**/

public class OpenConglomerateScratchSpace 
    implements DynamicCompiledOpenConglomInfo
{

    /**************************************************************************
     * Fields of the class
     **************************************************************************
     */

    /**
     * A template of info about the classes in the returned row.
     * <p>
     * This template is allocated on demand, and is used to efficiently
     * create new rows for export from this class.  This variable is for
     * use by get_row_for_export().
     **/
    private FormatableBitSet     row_for_export_column_list;
    private InstanceGetter[] row_for_export_class_template;

    /**
     * A Scratch template used for searching and qualifying rows in the 
     * conglomerate.  This is a full template, independent of the FormatableBitSet
     * used for access.
     **/
    private DataValueDescriptor[] scratch_template;

    /**
     * A Scratch row used for qualifying rows in the 
     * conglomerate.  This is a row which matches the FormatableBitSet of rows being
     * returned.
     **/
    private DataValueDescriptor[] scratch_row;

    /**
     * A complete array of format id's for this conglomerate.
     **/
    private int[]    format_ids;

    /**************************************************************************
     * Constructors for This class:
     **************************************************************************
     */
    public OpenConglomerateScratchSpace(
    int[]  format_ids)
    {
        this.format_ids = format_ids;
    }

    /**************************************************************************
     * Private/Protected methods of This class:
     **************************************************************************
     */

    /**************************************************************************
     * Public Methods of This class:
     **************************************************************************
     */

    /**
     * Return an empty template (possibly partial) row to be given back to 
     * a client.
     * <p>
     * The main use of this is for fetchSet() and fetchNextGroup() which
     * allocate rows and then give them back entirely to the caller.
     * <p>
     *
	 * @return The row to use.
     *
	 * @exception  StandardException  Standard exception policy.
     **/
    public DataValueDescriptor[] get_row_for_export()
        throws StandardException
    {
        // Create a partial row class template template from the initial scan
        // parameters.
        if (row_for_export_class_template == null)
        {
            row_for_export_class_template = 
                RowUtil.newClassInfoTemplate(
                    row_for_export_column_list, format_ids);
        }

        // Allocate a new row based on the class template.
        return(
            RowUtil.newRowFromClassInfoTemplate(row_for_export_class_template));
    }

    /**
     * Return an empty template (possibly partial) row to be used and 
     * reused internally for processing.
     * <p>
     * The main use of this is for qualifying rows where a row has not been
     * provided by the client.  This routine cache's a single row for reuse
     * by the caller, if the caller needs 2 concurrent scratch rows, some other
     * mechanism must be used.
     * <p>
     *
	 * @return The row to use.
     *
	 * @exception  StandardException  Standard exception policy.
     **/
    public DataValueDescriptor[] get_scratch_row()
        throws StandardException
    {
        // Create a partial row class template template from the initial scan
        // parameters.
        if (scratch_row == null)
        {
            scratch_row = get_row_for_export();
        }

        // Allocate a new row based on the class template.
        return(scratch_row);
    }

    /**
     * Return a complete empty row.  
     * <p>
     * The main use of this is for searching a tree where a complete copy of
     * the row is needed for searching.
     * <p>
     *
	 * @return The template to use.
     *
	 * @exception  StandardException  Standard exception policy.
     **/
    public DataValueDescriptor[] get_template()
        throws StandardException
    {
        // Create a partial row class template from the initial scan parameters.
        if (scratch_template == null)
        {
            scratch_template = TemplateRow.newRow((FormatableBitSet) null, format_ids);
        }

        return(scratch_template);
    }

    /**
     * Initialize scratch space for reuse by possibly different template.
     * <p>
     * Some data is only valid per statement.
     **/
    public void init(
    FormatableBitSet export_column_list)
    {
        row_for_export_class_template = null;
        row_for_export_column_list    = null;
    }
}