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242 lines
8.7 KiB
HTML
242 lines
8.7 KiB
HTML
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<?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>Implementing Key Creators</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 V1.73.2" />
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<link rel="start" href="index.html" title="Getting Started with Berkeley DB Java Edition" />
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<link rel="up" href="indexes.html" title="Chapter 10. Secondary Databases" />
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<link rel="prev" href="indexes.html" title="Chapter 10. Secondary Databases" />
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<link rel="next" href="secondaryProps.html" title="Secondary Database Properties" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 12.2.7.5</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Implementing Key
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<span xmlns="http://www.w3.org/1999/xhtml">Creators</span>
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</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="indexes.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 10. Secondary Databases</th>
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<td width="20%" align="right"> <a accesskey="n" href="secondaryProps.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="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="keyCreator"></a>Implementing Key
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<span>Creators</span>
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</h2>
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</div>
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</div>
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</div>
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<p>
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You must provide every secondary database with a
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<span>class</span>
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that creates keys from primary records. You identify this
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<span>class</span>
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<span>
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using the <code class="methodname">SecondaryConfig.setKeyCreator()</code>
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method.
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</span>
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</p>
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<p>
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You can create keys using whatever data you want. Typically you will
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base your key on some information found in a record's data, but you
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can also use information found in the primary record's key. How you build
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your keys is entirely dependent upon the nature of the index that you
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want to maintain.
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</p>
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<p>
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You implement a key creator by writing a class that implements the
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<code class="classname">SecondaryKeyCreator</code> interface. This interface
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requires you to implement the <code class="methodname">SecondaryKeyCreator.createSecondaryKey()</code>
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method.
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</p>
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<p>
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One thing to remember when implementing this method is that you will
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need a way to extract the necessary information from the data's
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<code class="classname">DatabaseEntry</code> and/or the key's
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<code class="classname">DatabaseEntry</code> that are provided on calls to this
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method. If you are using complex objects, then you are probably using the
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Bind APIs to perform this conversion. The easiest thing to do is to
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instantiate the <code class="classname">EntryBinding</code> or
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<code class="classname">TupleBinding</code> that you need to perform the
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conversion, and then provide this to your key creator's constructor.
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The Bind APIs are introduced in <a class="xref" href="bindAPI.html" title="Using the BIND APIs">Using the BIND APIs</a>.
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</p>
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<p>
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<code class="methodname">SecondaryKeyCreator.createSecondaryKey()</code> returns a
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boolean. A return value of <code class="literal">false</code> indicates that
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no secondary key exists, and therefore no record should be added to the secondary database for that primary record.
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If a record already exists in the secondary database, it is deleted.
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</p>
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<p>
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For example, suppose your primary database uses the following class
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for its record data:
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</p>
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<a id="je_index3"></a>
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<pre class="programlisting">package je.gettingStarted;
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public class PersonData {
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private String userID;
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private String surname;
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private String familiarName;
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public PersonData(String userID, String surname,
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String familiarName) {
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this.userID = userID;
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this.surname = surname;
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this.familiarName = familiarName;
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}
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public String getUserID() {
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return userID;
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}
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public String getSurname() {
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return surname;
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}
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public String getFamiliarName() {
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return familiarName;
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}
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} </pre>
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<p>
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Also, suppose that you have created a custom tuple binding,
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<code class="classname">PersonDataBinding</code>, that you use to convert
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<code class="classname">PersonData</code> objects to and from
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<code class="classname">DatabaseEntry</code> objects. (Custom tuple bindings are
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described in <a class="xref" href="bindAPI.html#customTuple" title="Custom Tuple Bindings">Custom Tuple Bindings</a>.)
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</p>
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<p>
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Finally, suppose you want a secondary database that is keyed based
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on the person's full name.
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</p>
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<p>
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Then in this case you might create a key creator as follows:
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</p>
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<a id="je_index4"></a>
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<pre class="programlisting">package je.gettingStarted;
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import com.sleepycat.bind.tuple.TupleBinding;
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import com.sleepycat.je.SecondaryKeyCreator;
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import com.sleepycat.je.DatabaseEntry;
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import com.sleepycat.je.DatabaseException;
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import com.sleepycat.je.SecondaryDatabase;
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import java.io.IOException;
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public class FullNameKeyCreator implements SecondaryKeyCreator {
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private TupleBinding theBinding;
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public FullNameKeyCreator(TupleBinding theBinding1) {
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theBinding = theBinding1;
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}
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public boolean createSecondaryKey(SecondaryDatabase secDb,
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DatabaseEntry keyEntry,
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DatabaseEntry dataEntry,
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DatabaseEntry resultEntry) {
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try {
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PersonData pd =
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(PersonData) theBinding.entryToObject(dataEntry);
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String fullName = pd.getFamiliarName() + " " +
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pd.getSurname();
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resultEntry.setData(fullName.getBytes("UTF-8"));
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} catch (IOException willNeverOccur) {}
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return true;
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}
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} </pre>
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<p>Finally, you use this key creator as follows:</p>
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<a id="je_index5"></a>
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<pre class="programlisting">package je.gettingStarted;
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import com.sleepycat.bind.tuple.TupleBinding;
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import com.sleepycat.je.Database;
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import com.sleepycat.je.DatabaseException;
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import com.sleepycat.je.Environment;
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import com.sleepycat.je.SecondaryDatabase;
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import com.sleepycat.je.SecondaryConfig;
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...
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Environment myEnv = null;
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Database myDb = null;
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SecondaryDatabase mySecDb = null;
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try {
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// Environment and primary database open omitted for brevity
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...
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TupleBinding myDataBinding = new MyTupleBinding();
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FullNameKeyCreator fnkc = new FullNameKeyCreator(myDataBinding);
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SecondaryConfig mySecConfig = new SecondaryConfig();
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mySecConfig.setKeyCreator(fnkc);
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//Perform the actual open
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String secDbName = "mySecondaryDatabase";
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mySecDb = myEnv.openSecondaryDatabase(null, secDbName, myDb,
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mySecConfig);
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} catch (DatabaseException de) {
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// Exception handling goes here
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} finally {
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try {
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if (mySecDb != null) {
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mySecDb.close();
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}
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if (myDb != null) {
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myDb.close();
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}
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if (myEnv != null) {
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myEnv.close();
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}
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} catch (DatabaseException dbe) {
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// Exception handling goes here
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}
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}</pre>
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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="indexes.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="indexes.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="secondaryProps.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">Chapter 10. Secondary Databases </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"> Secondary Database Properties</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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