Quadcap Embeddable Database

com/quadcap/sql/AlterColumn.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.
 *
 * Redistributions in binary form must reproduce this Copyright Notice,
 * these license terms, and the disclaimer/limitation of liability set
 * forth as paragraph 6 below, in the documentation and/or other materials
 * provided with the distribution.
 *
 * The Software is provided on an "AS IS" basis.  No warranty is
 * provided that the Software is free of defects, or fit for a
 * particular purpose.  
 *
 * Limitation of Liability. Quadcap Software shall not be liable
 * for any damages suffered by the Licensee or any third party resulting
 * from use of the Software.
 */

import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;

import java.sql.SQLException;

import com.quadcap.sql.io.Extern;

import com.quadcap.util.Debug;

/**
 * Log Step to alter the definition of a table column.
 *
 * @author Stan Bailes
 */
public class AlterColumn extends LogStep implements Externalizable {
    transient Table                     table;
    transient Column                    column;

    String                              columnName              = null;
    String                              tableName               = null;
    Expression                          oldDefault              = null;
    Expression                          newDefault              = null;

    /**
     * Default constructor
     */
    public AlterColumn() {}

    /**
     * Explicit constructor from table, column name and new default value
     */
    public AlterColumn(Session session, Table table,
                       String columnName, Expression newDefault) {
        super(session);
        this.table = table;
        this.tableName = table.getName();
        this.columnName = columnName;
        this.newDefault = newDefault;
    }

    Table getTable(Database db) throws IOException {
        if (table == null) {
            table = (Table)db.getRelation(tableName);
        }
        return table;
    }
        
    public void undo(Session session) throws IOException, SQLException {
        Database db = session.getDatabase();
        getTable(db);
        column = table.getColumn(columnName);
        column.setDefault(oldDefault);
        db.updateRelation(table);
    }

    public void redo(Session session) throws IOException, SQLException {
        Database db = session.getDatabase();
        getTable(db);
        column.setDefault(newDefault);
        db.updateRelation(table);
    }

    public void prepare(Session session) throws IOException, SQLException {
        column = table.getColumn(columnName);
        if (oldDefault == null) {
            oldDefault = column.getDefault();
        }
    }
    
    public void readExternal(ObjectInput in)
        throws IOException, ClassNotFoundException
    {
        super.readExternal(in);
        this.columnName = (String)in.readObject();
        this.tableName = (String)in.readObject();
        this.oldDefault = (Expression)in.readObject();
        this.newDefault = (Expression)in.readObject();
    }
    
    public void writeExternal(ObjectOutput out) throws IOException {
        super.writeExternal(out);
        out.writeObject(columnName);
        out.writeObject(tableName);
        out.writeObject(oldDefault);
        out.writeObject(newDefault);
    }

    //#ifdef DEBUG
    public String toString() {
        StringBuffer sb = new StringBuffer(super.toString());
        sb.append(" AlterColumn(");
        sb.append(tableName);
        sb.append(',');
        sb.append(columnName);
        sb.append(" set default " + newDefault);
        sb.append(")");
        return sb.toString();
    }
    //#endif

    static Extern                       extern = null;
    public Extern getExtern() { return extern; }
    public void setExtern(Extern extern) { AlterColumn.extern = extern; }
}