1<?xml version="1.0" encoding="UTF-8" standalone="no"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml"> 4 <head> 5 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> 6 <title>Chapter 10. Secondary Databases</title> 7 <link rel="stylesheet" href="gettingStarted.css" type="text/css" /> 8 <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> 9 <link rel="start" href="index.html" title="Getting Started with Berkeley DB" /> 10 <link rel="up" href="baseapi.html" title="Part II. Programming with the Base API" /> 11 <link rel="prev" href="cursorJavaUsage.html" title="Cursor Example" /> 12 <link rel="next" href="keyCreator.html" title="Implementing Key Creators" /> 13 </head> 14 <body> 15 <div class="navheader"> 16 <table width="100%" summary="Navigation header"> 17 <tr> 18 <th colspan="3" align="center">Chapter 10. Secondary Databases</th> 19 </tr> 20 <tr> 21 <td width="20%" align="left"><a accesskey="p" href="cursorJavaUsage.html">Prev</a> </td> 22 <th width="60%" align="center">Part II. Programming with the Base API</th> 23 <td width="20%" align="right"> <a accesskey="n" href="keyCreator.html">Next</a></td> 24 </tr> 25 </table> 26 <hr /> 27 </div> 28 <div class="chapter" lang="en" xml:lang="en"> 29 <div class="titlepage"> 30 <div> 31 <div> 32 <h2 class="title"><a id="indexes"></a>Chapter 10. Secondary Databases</h2> 33 </div> 34 </div> 35 </div> 36 <div class="toc"> 37 <p> 38 <b>Table of Contents</b> 39 </p> 40 <dl> 41 <dt> 42 <span class="sect1"> 43 <a href="indexes.html#DbAssociate">Opening and Closing Secondary Databases</a> 44 </span> 45 </dt> 46 <dt> 47 <span class="sect1"> 48 <a href="keyCreator.html">Implementing Key 49 <span>Creators</span> 50 51 </a> 52 </span> 53 </dt> 54 <dd> 55 <dl> 56 <dt> 57 <span class="sect2"> 58 <a href="keyCreator.html#multikeys">Working with Multiple Keys</a> 59 </span> 60 </dt> 61 </dl> 62 </dd> 63 <dt> 64 <span class="sect1"> 65 <a href="secondaryProps.html">Secondary Database Properties</a> 66 </span> 67 </dt> 68 <dt> 69 <span class="sect1"> 70 <a href="readSecondary.html">Reading Secondary Databases</a> 71 </span> 72 </dt> 73 <dt> 74 <span class="sect1"> 75 <a href="secondaryDelete.html">Deleting Secondary Database Records</a> 76 </span> 77 </dt> 78 <dt> 79 <span class="sect1"> 80 <a href="secondaryCursor.html"> 81 <span>Using Secondary Cursors</span> 82 83 </a> 84 </span> 85 </dt> 86 <dt> 87 <span class="sect1"> 88 <a href="joins.html">Database Joins</a> 89 </span> 90 </dt> 91 <dd> 92 <dl> 93 <dt> 94 <span class="sect2"> 95 <a href="joins.html#joinUsage">Using Join Cursors</a> 96 </span> 97 </dt> 98 <dt> 99 <span class="sect2"> 100 <a href="joins.html#joinconfig">JoinCursor Properties</a> 101 </span> 102 </dt> 103 </dl> 104 </dd> 105 <dt> 106 <span class="sect1"> 107 <a href="javaindexusage.html">Secondary Database Example</a> 108 </span> 109 </dt> 110 <dd> 111 <dl> 112 <dt> 113 <span class="sect2"> 114 <a href="javaindexusage.html#secondaryMyDbs">Opening Secondary Databases with MyDbs</a> 115 </span> 116 </dt> 117 <dt> 118 <span class="sect2"> 119 <a href="javaindexusage.html#exampleReadJavaSecondaries">Using Secondary Databases with ExampleDatabaseRead</a> 120 </span> 121 </dt> 122 </dl> 123 </dd> 124 </dl> 125 </div> 126 <p> 127 Usually you find database records by means of the record's key. However, 128 the key that you use for your record will not always contain the 129 information required to provide you with rapid access to the data that you 130 want to retrieve. For example, suppose your 131 <code class="classname">Database</code> 132 133 contains records related to users. The key might be a string that is some 134 unique identifier for the person, such as a user ID. Each record's data, 135 however, would likely contain a complex object containing details about 136 people such as names, addresses, phone numbers, and so forth. 137 While your application may frequently want to query a person by user 138 ID (that is, by the information stored in the key), it may also on occasion 139 want to locate people by, say, their name. 140 </p> 141 <p> 142 Rather than iterate through all of the records in your database, examining 143 each in turn for a given person's name, you create indexes based on names 144 and then just search that index for the name that you want. You can do this 145 using secondary databases. In DB, the 146 <code class="classname">Database</code> 147 148 that contains your data is called a 149 <span class="emphasis"><em>primary database</em></span>. A database that provides an 150 alternative set of keys to access that data is called a <span class="emphasis"><em>secondary 151 database</em></span> In a secondary database, the keys are your alternative 152 (or secondary) index, and the data corresponds to a primary record's key. 153 </p> 154 <p> 155 You create a secondary database by using a <code class="classname">SecondaryConfig</code> 156 class object to identify an implementation of a 157 <code class="classname">SecondaryKeyCreator</code> 158 class object that is used to create keys based on data found in the primary 159 database. You then pass this <code class="classname">SecondaryConfig</code> 160 object to the <code class="classname">SecondaryDatabase</code> constructor. 161 </p> 162 <p> 163 Once opened, DB manages secondary databases for you. Adding or deleting 164 records in your primary database causes DB to update the secondary as 165 necessary. Further, changing a record's data in the primary database may cause 166 DB to modify a record in the secondary, depending on whether the change 167 forces a modification of a key in the secondary database. 168 </p> 169 <p> 170 Note that you can not write directly to a secondary database. 171 172 173 174 175 176 To change the data referenced by a 177 <code class="classname">SecondaryDatabase</code> 178 179 record, modify the primary database instead. The exception to this rule is 180 that delete operations are allowed on the 181 <span><code class="classname">SecondaryDatabase</code> object.</span> 182 183 184 See <a class="xref" href="secondaryDelete.html" title="Deleting Secondary Database Records">Deleting Secondary Database Records</a> for more 185 information. 186 </p> 187 <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"> 188 <h3 class="title">Note</h3> 189 <p> 190 191 Secondary database records are updated/created by DB 192 only if the 193 <span><code class="methodname">SecondaryKeyCreator.createSecondaryKey()</code> method</span> 194 195 returns 196 <span><code class="literal">true</code>.</span> 197 198 If 199 <code class="literal">false</code> 200 201 is returned, then DB will not add the key to the secondary database, and 202 in the event of a record update it will remove any existing key. 203 204 205 206 </p> 207 <p> 208 See <a class="xref" href="keyCreator.html" title="Implementing Key Creators">Implementing Key 209 <span>Creators</span> 210 211 </a> for more 212 <span>information on this interface and method.</span> 213 214 215 </p> 216 </div> 217 <p> 218 When you read a record from a secondary database, DB automatically 219 returns 220 221 <span>the data and optionally the key</span> 222 from the corresponding record in the primary database. 223 224 </p> 225 <div class="sect1" lang="en" xml:lang="en"> 226 <div class="titlepage"> 227 <div> 228 <div> 229 <h2 class="title" style="clear: both"><a id="DbAssociate"></a>Opening and Closing Secondary Databases</h2> 230 </div> 231 </div> 232 </div> 233 <p> 234 You manage secondary database opens and closes using the 235 236 <span> 237 <code class="classname">SecondaryDatabase</code> constructor. 238 </span> 239 Just as is the case with primary databases, you must provide 240 241 <span> 242 the <code class="classname">SecondaryDatabase()</code> constructor 243 </span> 244 with the database's 245 name and, optionally, other properties such as whether duplicate 246 records are allowed, or whether the secondary database can be created on 247 open. In addition, you must also provide: 248 </p> 249 <div class="itemizedlist"> 250 <ul type="disc"> 251 <li> 252 <p>A handle to the primary database that this secondary database is 253 indexing. Note that this means that secondary databases are maintained 254 only for the specified <code class="classname">Database</code> handle. If you 255 open the same <code class="classname">Database</code> multiple times for write 256 (such as might occur when opening a database for read-only and read-write in the same application), 257 then you should open the <code class="classname">SecondaryDatabase</code> for 258 each such <code class="classname">Database</code> handle.</p> 259 </li> 260 <li> 261 <p>A <code class="classname">SecondaryConfig</code> object that provides 262 properties specific to a secondary database. The most important of 263 these is used to identify the key creator for the database. The key 264 creator is responsible for generating keys for the secondary database. 265 See <a class="xref" href="secondaryProps.html" title="Secondary Database Properties">Secondary Database Properties</a> for details.</p> 266 </li> 267 </ul> 268 </div> 269 <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"> 270 <h3 class="title">Note</h3> 271 <p> 272 Primary databases <span class="emphasis"><em>must not</em></span> support duplicate records. 273 Secondary records point to primary records using the primary key, so that key must be unique. 274 </p> 275 </div> 276 <p>So to open (create) a secondary database, you:</p> 277 <div class="orderedlist"> 278 <ol type="1"> 279 <li> 280 <p>Open your primary database.</p> 281 </li> 282 <li> 283 <p>Instantiate your key creator.</p> 284 </li> 285 <li> 286 <p>Instantiate your <code class="classname">SecondaryConfig</code> object.</p> 287 </li> 288 <li> 289 <p>Set your key creator object on your <code class="classname">SecondaryConfig</code> 290 object.</p> 291 </li> 292 <li> 293 <p>Open your secondary database, specifying your primary database 294 and your <code class="classname">SecondaryConfig</code> at that time.</p> 295 </li> 296 </ol> 297 </div> 298 <p>For example:</p> 299 <a id="java_index1"></a> 300 <pre class="programlisting">package db.GettingStarted; 301 302import com.sleepycat.bind.tuple.TupleBinding; 303import com.sleepycat.db.Database; 304import com.sleepycat.db.DatabaseType; 305import com.sleepycat.db.DatabaseConfig; 306import com.sleepycat.db.DatabaseException; 307import com.sleepycat.db.SecondaryDatabase; 308import com.sleepycat.db.SecondaryConfig; 309 310import java.io.FileNotFoundException; 311 312... 313 314DatabaseConfig myDbConfig = new DatabaseConfig(); 315myDbConfig.setAllowCreate(true); 316myDbConfig.setType(DatabaseType.BTREE); 317 318SecondaryConfig mySecConfig = new SecondaryConfig(); 319mySecConfig.setAllowCreate(true); 320mySecConfig.setType(DatabaseType.BTREE); 321// Duplicates are frequently required for secondary databases. 322mySecConfig.setSortedDuplicates(true); 323 324// Open the primary 325Database myDb = null; 326SecondaryDatabase mySecDb = null; 327try { 328 String dbName = "myPrimaryDatabase"; 329 330 myDb = new Database(dbName, null, myDbConfig); 331 332 // A fake tuple binding that is not actually implemented anywhere. 333 // The tuple binding is dependent on the data in use. 334 // Tuple bindings are described earlier in this manual. 335 TupleBinding myTupleBinding = new MyTupleBinding(); 336 337 // Open the secondary. 338 // Key creators are described in the next section. 339 FullNameKeyCreator keyCreator = new FullNameKeyCreator(myTupleBinding); 340 341 // Get a secondary object and set the key creator on it. 342 mySecConfig.setKeyCreator(keyCreator); 343 344 // Perform the actual open 345 String secDbName = "mySecondaryDatabase"; 346 mySecDb = new SecondaryDatabase(secDbName, null, myDb, mySecConfig); 347} catch (DatabaseException de) { 348 // Exception handling goes here ... 349} catch (FileNotFoundException fnfe) { 350 // Exception handling goes here ... 351}</pre> 352 <p>To close a secondary database, call its close() method. Note that 353 for best results, you should close all the secondary databases associated 354 with a primary database before closing the primary.</p> 355 <p>For example:</p> 356 <a id="java_index2"></a> 357 <pre class="programlisting">try { 358 if (mySecDb != null) { 359 mySecDb.close(); 360 } 361 362 if (myDb != null) { 363 myDb.close(); 364 } 365} catch (DatabaseException dbe) { 366 // Exception handling goes here 367}</pre> 368 </div> 369 </div> 370 <div class="navfooter"> 371 <hr /> 372 <table width="100%" summary="Navigation footer"> 373 <tr> 374 <td width="40%" align="left"><a accesskey="p" href="cursorJavaUsage.html">Prev</a> </td> 375 <td width="20%" align="center"> 376 <a accesskey="u" href="baseapi.html">Up</a> 377 </td> 378 <td width="40%" align="right"> <a accesskey="n" href="keyCreator.html">Next</a></td> 379 </tr> 380 <tr> 381 <td width="40%" align="left" valign="top">Cursor Example </td> 382 <td width="20%" align="center"> 383 <a accesskey="h" href="index.html">Home</a> 384 </td> 385 <td width="40%" align="right" valign="top"> Implementing Key 386 <span>Creators</span> 387 388 </td> 389 </tr> 390 </table> 391 </div> 392 </body> 393</html> 394