192 lines
6.4 KiB
HTML
192 lines
6.4 KiB
HTML
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Chapter 2. Databases</title>
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<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.62.4" />
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<link rel="home" href="index.html" title="Getting Started with Berkeley DB" />
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<link rel="up" href="index.html" title="Getting Started with Berkeley DB" />
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<link rel="previous" href="gettingit.html" title="Getting and Using DB " />
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<link rel="next" href="coredbclose.html" title="Closing Databases" />
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</head>
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<body>
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<div class="navheader">
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Chapter 2. Databases</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="gettingit.html">Prev</a> </td>
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<th width="60%" align="center"> </th>
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<td width="20%" align="right"> <a accesskey="n" href="coredbclose.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="chapter" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title"><a id="DB"></a>Chapter 2. Databases</h2>
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</div>
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</div>
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<div></div>
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</div>
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<div class="toc">
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<p>
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<b>Table of Contents</b>
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</p>
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<dl>
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<dt>
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<span class="sect1">
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<a href="DB.html#DBOpen">Opening Databases</a>
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</span>
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</dt>
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<dt>
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<span class="sect1">
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<a href="coredbclose.html">Closing Databases</a>
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</span>
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</dt>
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<dt>
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<span class="sect1">
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<a href="DBOpenFlags.html">Database Open Flags</a>
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</span>
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</dt>
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<dt>
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<span class="sect1">
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<a href="CoreDBAdmin.html">Administrative Methods</a>
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</span>
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</dt>
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<dt>
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<span class="sect1">
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<a href="dbErrorReporting.html">Error Reporting Functions</a>
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</span>
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</dt>
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<dt>
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<span class="sect1">
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<a href="CoreEnvUsage.html">Managing Databases in Environments</a>
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</span>
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</dt>
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<dt>
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<span class="sect1">
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<a href="CoreDbUsage.html">Database Example</a>
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</span>
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</dt>
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</dl>
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</div>
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<p>In Berkeley DB, a database is a collection of <span class="emphasis"><em>records</em></span>. Records,
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in turn, consist of key/data pairings.
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</p>
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<p>
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Conceptually, you can think of a
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<span>database</span>
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as containing a two-column table where column 1 contains a key and column 2
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contains data. Both the key and the data are managed using
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<tt class="classname">DBT</tt>
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<span>structures</span>
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(see <a href="DBEntry.html">Database Records</a> for details on this
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<span>structure</span>).
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So, fundamentally, using a DB
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<span>database</span>
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involves putting, getting, and deleting database records, which in turns involves efficiently
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managing information
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<span>contained in </span>
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<tt class="classname">DBT</tt>
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<span>structures.</span>
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The next several chapters of this book are dedicated to those activities.
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</p>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="DBOpen"></a>Opening Databases</h2>
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</div>
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</div>
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<div></div>
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</div>
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<p>
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To open a database, you must first use the <tt class="function">db_create()</tt> function to
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initialize a <tt class="classname">DB</tt> handle.
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Once you have initialized the <tt class="classname">DB</tt>
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handle, you use its <tt class="methodname">open()</tt> method to open the database.
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</p>
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<p>
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Note that by default, DB does not create databases if they do not already exist.
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To override this behavior, specify the
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<a href="DBOpenFlags.html" title="Database Open Flags"><tt class="literal">DB_CREATE</tt></a> flag on the
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<tt class="methodname">open()</tt> method.
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</p>
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<p>
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The following code fragment illustrates a database open:
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</p>
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<a id="c_db1"></a>
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<pre class="programlisting">#include <db.h>
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...
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DB *dbp; /* DB structure handle */
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u_int32_t flags; /* database open flags */
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int ret; /* function return value */
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/* Initialize the structure. This
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* database is not opened in an environment,
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* so the environment pointer is NULL. */
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ret = db_create(&dbp, NULL, 0);
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if (ret != 0) {
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/* Error handling goes here */
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}
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/* Database open flags */
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flags = DB_CREATE; /* If the database does not exist,
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* create it.*/
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/* open the database */
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ret = dbp->open(dbp, /* DB structure pointer */
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NULL, /* Transaction pointer */
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"my_db.db", /* On-disk file that holds the database. */
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NULL, /* Optional logical database name */
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DB_BTREE, /* Database access method */
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flags, /* Open flags */
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0); /* File mode (using defaults) */
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if (ret != 0) {
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/* Error handling goes here */
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}</pre>
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</div>
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</div>
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<div class="navfooter">
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<hr />
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||
<table width="100%" summary="Navigation footer">
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||
<tr>
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||
<td width="40%" align="left"><a accesskey="p" href="gettingit.html">Prev</a> </td>
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||
<td width="20%" align="center">
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<a accesskey="u" href="index.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="coredbclose.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">Getting and Using DB </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> Closing Databases</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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