Quadcap Embeddable Database

com/quadcap/sql/StmtAddColumn.java

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package com.quadcap.sql;

/* Copyright 1999 - 2003 Quadcap Software.  All rights reserved.
 *
 * This software is distributed under the Quadcap Free Software License.
 * This software may be used or modified for any purpose, personal or
 * commercial.  Open Source redistributions are permitted.  Commercial
 * redistribution of larger works derived from, or works which bundle
 * this software requires a "Commercial Redistribution License"; see
 * http://www.quadcap.com/purchase.
 *
 * Redistributions qualify as "Open Source" under  one of the following terms:
 *   
 *    Redistributions are made at no charge beyond the reasonable cost of
 *    materials and delivery.
 *
 *    Redistributions are accompanied by a copy of the Source Code or by an
 *    irrevocable offer to provide a copy of the Source Code for up to three
 *    years at the cost of materials and delivery.  Such redistributions
 *    must allow further use, modification, and redistribution of the Source
 *    Code under substantially the same terms as this license.
 *
 * Redistributions of source code must retain the copyright notices as they
 * appear in each source code file, these license terms, and the
 * disclaimer/limitation of liability set forth as paragraph 6 below.
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 * Redistributions in binary form must reproduce this Copyright Notice,
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 * The Software is provided on an "AS IS" basis.  No warranty is
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 *
 * Limitation of Liability. Quadcap Software shall not be liable
 * for any damages suffered by the Licensee or any third party resulting
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 */

import java.io.IOException;

import java.util.Vector;

import java.sql.SQLException;

import com.quadcap.sql.file.BlockFile;
import com.quadcap.sql.file.ByteUtil;

import com.quadcap.sql.index.Btree;
import com.quadcap.sql.index.BCursor;

import com.quadcap.sql.types.Value;
import com.quadcap.sql.types.ValueLong;
import com.quadcap.sql.types.ValueNull;

import com.quadcap.util.Debug;

/**
 * Implementation of SQL <b>ADD COLUMN</b> statement.
 *
 * @author Stan Bailes
 */
public class StmtAddColumn implements Stmt {
    String                              tableName;
    Column                              column;
    String                              aname;

    /**
     * Explicit constructor from table name and Column
     */
    public StmtAddColumn(String tableName, Column column, String aname) {
        this.tableName = tableName;
        this.column = column;
        this.aname = aname;
    }

    /**
     * Stmt.execute()
     *
     * For ADD COLUMN, we need to update the table definition, of course.
     * But then, we need to update *all* of the rows!
     */
    public void execute(Session session) throws IOException, SQLException {
        // First, acquire the schema and table locks       
        Database db = session.getDatabase();
        session.getTableWriteLock("#Schema");
        session.getTableWriteLock(tableName);

        // Make a cursor from the original schema
        Table table = (Table)db.getRelation(tableName);
        if (table == null) {
            throw new SQLException("Table not found: " + tableName);
        }

        if (table.getColumnIndex(column.getName()) >= 1) {
            throw new SQLException("Add Column: a column named '" +
                                   column.getName() +
                                   "' already exists int table '" +
                                   tableName + "'");
        }

        int newpos = table.getColumnCount() + 1;
        if (aname != null) {
            if (aname.equals("")) {
                newpos = 1;
            } else {
                newpos = table.getColumnIndex(aname) + 1;
                if (newpos <= 0) {
                    throw new SQLException("Bad column name: " + aname);
                }
            }
        }
        column.setColumn(newpos);

        // Update every row in the table with the new column value
        BCursor bc = null;
        try {
            long id = 0;
            BlockFile file = db.getFile();
            Expression defaultExpr = column.getDefault();
            Value columnDefault = 
                defaultExpr == null ? ValueNull.valueNull 
                : defaultExpr.getValue(session, null);
            
            IndexConstraint ic = table.getAnyIndex(session);
            Btree index = ic.getIndex(db);
            bc = index.getCursor(false);
            LazyRow row1 = new LazyRow(table.getColumnCount());
            Row row2 = new Row(table.getColumnCount() + 1);
            while (bc.next()) {
                long rowId = bc.getValAsLong();
                db.getRow(rowId, row1, false);
                int offset = 0;
                for (int i = 1; i <= row2.size(); i++) {
                    if (i == newpos) {
                        if (column.isAutoIncrement()) {
                            columnDefault = new ValueLong(++id);
                        }
                        row2.set(i, columnDefault);
                        offset = 1;
                    } else {
                        row2.set(i, row1.item(i - offset));
                    }
                }
                UpdateRow update = null;
                if (db.inMemory()) {
                    update = new UpdateRow(session, rowId, row1, row2);
                    row2 = new Row(table.getColumnCount() + 1);
                    row1 = new LazyRow(table.getColumnCount());
                } else {
                    byte[] oldRowBytes = row1.getBytes();
                    byte[] rowBytes = LazyRow.writeRow(session, null, row2);
                    update = new UpdateRow(session, table, rowId,
                                           oldRowBytes, rowBytes);
                }
                session.doStep(update);
            }
            if (column.isAutoIncrement()) {
                session.doStep(new AutoNumberStep(session, table, id+1));
            }
        } finally {
            if (bc != null) bc.release();
        }

        // This changes the table schema
        session.doStep(new AddColumn(session, table, column, newpos));

        Vector cv = column.getConstraints();
        if (cv != null) for (int i = 0; i < cv.size(); i++) {
            Constraint constraint = (Constraint)cv.elementAt(i);
            session.doStep(new AddConstraint(session, table, constraint));
        }

        table.resetColumnConstraints();
    }
}