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Java > Open Source Codes > com > quadcap > sql > DropColumn


1 package com.quadcap.sql;
2
3 /* Copyright 1999 - 2003 Quadcap Software. All rights reserved.
4  *
5  * This software is distributed under the Quadcap Free Software License.
6  * This software may be used or modified for any purpose, personal or
7  * commercial. Open Source redistributions are permitted. Commercial
8  * redistribution of larger works derived from, or works which bundle
9  * this software requires a "Commercial Redistribution License"; see
10  * http://www.quadcap.com/purchase.
11  *
12  * Redistributions qualify as "Open Source" under one of the following terms:
13  *
14  * Redistributions are made at no charge beyond the reasonable cost of
15  * materials and delivery.
16  *
17  * Redistributions are accompanied by a copy of the Source Code or by an
18  * irrevocable offer to provide a copy of the Source Code for up to three
19  * years at the cost of materials and delivery. Such redistributions
20  * must allow further use, modification, and redistribution of the Source
21  * Code under substantially the same terms as this license.
22  *
23  * Redistributions of source code must retain the copyright notices as they
24  * appear in each source code file, these license terms, and the
25  * disclaimer/limitation of liability set forth as paragraph 6 below.
26  *
27  * Redistributions in binary form must reproduce this Copyright Notice,
28  * these license terms, and the disclaimer/limitation of liability set
29  * forth as paragraph 6 below, in the documentation and/or other materials
30  * provided with the distribution.
31  *
32  * The Software is provided on an "AS IS" basis. No warranty is
33  * provided that the Software is free of defects, or fit for a
34  * particular purpose.
35  *
36  * Limitation of Liability. Quadcap Software shall not be liable
37  * for any damages suffered by the Licensee or any third party resulting
38  * from use of the Software.
39  */
40
41 import java.io.BufferedInputStream JavaDoc;
42 import java.io.BufferedOutputStream JavaDoc;
43 import java.io.Externalizable JavaDoc;
44 import java.io.IOException JavaDoc;
45 import java.io.ObjectInput JavaDoc;
46 import java.io.ObjectOutput JavaDoc;
47
48 import java.sql.SQLException JavaDoc;
49
50 import com.quadcap.sql.file.BlockFile;
51 import com.quadcap.sql.file.ByteUtil;
52 import com.quadcap.sql.file.PageManager;
53 import com.quadcap.sql.file.RandomAccess;
54 import com.quadcap.sql.file.RandomAccessInputStream;
55 import com.quadcap.sql.file.RandomAccessOutputStream;
56
57 import com.quadcap.sql.io.ObjectInputStream;
58 import com.quadcap.sql.io.ObjectOutputStream;
59 import com.quadcap.sql.io.Extern;
60
61 import com.quadcap.sql.index.Btree;
62
63 import com.quadcap.sql.types.Value;
64 import com.quadcap.sql.types.ValueNull;
65
66 import com.quadcap.io.CountedInputStream;
67
68 import com.quadcap.util.Debug;
69
70 /**
71  * Log step to add a column to a table, supplying default values as necessary.
72  *
73  * @author Stan Bailes
74  */
75 public class DropColumn extends LogStep implements Externalizable JavaDoc {
76     transient Table table;
77
78     Column column;
79     String JavaDoc tableName = null;
80
81     /**
82      * Default constructor
83      */
84     public DropColumn() {}
85
86     /**
87      * Explicit constructor from table and column
88      */
89     public DropColumn(Session session, Table table, Column column) {
90         super(session);
91     this.table = table;
92     this.tableName = table.getName();
93     this.column = column;
94     }
95
96     /**
97      * Lazy table accessor
98      */
99     Table getTable(Database db) throws IOException JavaDoc {
100     if (table == null) {
101         table = (Table)db.getRelation(tableName);
102     }
103     return table;
104     }
105
106     /**
107      * LogStep.redo(), our job is to remove the column definition from the
108      * schema.
109      */
110     public void redo(Session session) throws IOException JavaDoc, SQLException JavaDoc {
111     Database db = session.getDatabase();
112     getTable(db);
113     Column c = table.getColumn(column.getName());
114     table.deleteColumn(c.getColumn());
115     db.updateRelation(table);
116     }
117
118     /**
119      * LogStep.undo(), our job is to update the table's definition to
120      * include the new column
121      */
122     public void undo(Session session) throws IOException JavaDoc, SQLException JavaDoc {
123     Database db = session.getDatabase();
124     getTable(db);
125     table.addColumn(column, column.getColumn());
126     db.updateRelation(table);
127     }
128
129     /**
130      * I'm ready
131      */
132     public void prepare(Session session) throws IOException JavaDoc, SQLException JavaDoc {
133     }
134
135     /**
136      * Read me from a stream
137      */
138     public void readExternal(ObjectInput JavaDoc in)
139     throws IOException JavaDoc, ClassNotFoundException JavaDoc
140     {
141     super.readExternal(in);
142     this.column = (Column)in.readObject();
143     this.tableName = (String JavaDoc)in.readObject();
144     }
145
146     /**
147      * Write me to a stream
148      */
149     public void writeExternal(ObjectOutput JavaDoc out) throws IOException JavaDoc {
150     super.writeExternal(out);
151     out.writeObject(column);
152     out.writeObject(tableName);
153     }
154
155     /**
156      * Return a string representation for display/debugging purposes
157      */
158     //#ifdef DEBUG
159 public String JavaDoc toString() {
160     StringBuffer JavaDoc sb = new StringBuffer JavaDoc(super.toString());
161         sb.append(" DropColumn(");
162     sb.append(tableName);
163     sb.append(',');
164     sb.append(column.toString());
165     return sb.toString();
166     }
167     //#endif
168
169     /**
170      * My class's Extern object (see com.quadcap.sql.io.Extern)
171      */
172     static Extern extern;
173     public void setExtern(Extern extern) { DropColumn.extern = extern; }
174     public Extern getExtern() { return extern; }
175 }
176
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