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8.4 KiB
HTML
244 lines
8.4 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>Chapter 5. Saving and Retrieving Objects</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="dpl.html" title="Part I. Programming with the Direct Persistence Layer" />
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<link rel="prev" href="dplindexcreate.html" title="Creating Indexes" />
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<link rel="next" href="simpleda.html" title="SimpleDA.class" />
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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">Chapter 5. Saving and Retrieving Objects</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="dplindexcreate.html">Prev</a> </td>
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<th width="60%" align="center">Part I. Programming with the Direct Persistence Layer</th>
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<td width="20%" align="right"> <a accesskey="n" href="simpleda.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="persist_access"></a>Chapter 5. Saving and Retrieving Objects</h2>
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</div>
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</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="persist_access.html#simpleentity">A Simple Entity Class</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="simpleda.html">SimpleDA.class</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="simpleput.html">Placing Objects in an Entity Store</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="simpleget.html">Retrieving Objects from an Entity Store</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="getmultiple.html">Retrieving Multiple Objects</a>
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</span>
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</dt>
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<dd>
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<dl>
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<dt>
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<span class="sect2">
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<a href="getmultiple.html#dpl_cursor_initialize">Cursor Initialization</a>
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</span>
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</dt>
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<dt>
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<span class="sect2">
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<a href="getmultiple.html#dpl_dups">Working with Duplicate Keys</a>
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</span>
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</dt>
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<dt>
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<span class="sect2">
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<a href="getmultiple.html#dpl_cursor_range">Key Ranges</a>
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</span>
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</dt>
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</dl>
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</dd>
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<dt>
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<span class="sect1">
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<a href="dpl_entityjoin.html">Join Cursors</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="dpl_delete.html">Deleting Entity Objects</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="dpl_replace.html">Replacing Entity Objects</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>
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To store an object in an <code class="classname">EntityStore</code> you
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must annotate the class appropriately and then store it using
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<code class="methodname">PrimaryIndex.put()</code>.
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</p>
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<p>
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To retrieve and object from an <code class="classname">EntityStore</code>
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you use the <code class="methodname">get()</code> method from either the
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<code class="classname">PrimaryIndex</code> or
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<code class="classname">SecondaryIndex</code>, whichever is most
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appropriate for your application.
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</p>
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<p>
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In both cases, it simplifies things greatly if you create a data
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accessor class to organize your indexes.
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</p>
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<p>
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In the next few sections we:
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</p>
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<div class="orderedlist">
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<ol type="1">
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<li>
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<p>
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Create an entity class that is ready to be stored
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in an entity store. This class will have both a
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primary index (required) declared for it, as well
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as a secondary index (which is optional).
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</p>
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<p>
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See the next section for this implementation.
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</p>
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</li>
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<li>
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<p>
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Create a data accessor class which is used to
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organize our data.
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</p>
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<p>
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See <a class="xref" href="simpleda.html" title="SimpleDA.class">SimpleDA.class</a>
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for this implementation.
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</p>
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</li>
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<li>
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<p>
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Create a simple class that is used to put objects
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to our entity store.
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</p>
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<p>
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See <a class="xref" href="simpleput.html" title="Placing Objects in an Entity Store">Placing Objects in an Entity Store</a>
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for this implementation.
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</p>
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</li>
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<li>
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<p>
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Create another class that retrieves objects from
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our entity store.
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</p>
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<p>
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See <a class="xref" href="simpleget.html" title="Retrieving Objects from an Entity Store">Retrieving Objects from an Entity Store</a>
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for this implementation.
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</p>
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</li>
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</ol>
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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="simpleentity"></a>A Simple Entity Class</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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For clarity's sake, this entity class is as simple a class as we can write.
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It contains only two data members, both of which are set
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and retrieved by simple setter and getter methods. Beyond
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that, by design this class does not do anything of particular
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interest.
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</p>
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<p>
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Its implementation is as follows:
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</p>
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<pre class="programlisting">package persist.gettingStarted;
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import com.sleepycat.persist.model.Entity;
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import com.sleepycat.persist.model.PrimaryKey;
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import static com.sleepycat.persist.model.Relationship.*;
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import com.sleepycat.persist.model.SecondaryKey;
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@Entity
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public class SimpleEntityClass {
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// Primary key is pKey
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@PrimaryKey
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private String pKey;
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// Secondary key is the sKey
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@SecondaryKey(relate=MANY_TO_ONE)
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private String sKey;
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public void setPKey(String data) {
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pKey = data;
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}
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public void setSKey(String data) {
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sKey = data;
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}
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public String getPKey() {
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return pKey;
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}
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public String getSKey() {
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return sKey;
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}
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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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|||
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<td width="40%" align="left"><a accesskey="p" href="dplindexcreate.html">Prev</a> </td>
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<td width="20%" align="center">
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|||
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<a accesskey="u" href="dpl.html">Up</a>
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</td>
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|||
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<td width="40%" align="right"> <a accesskey="n" href="simpleda.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">Creating Indexes </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"> SimpleDA.class</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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