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246 lines
10 KiB
HTML
246 lines
10 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 4. Working with Indices</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="saveret.html" title="Saving and Retrieving Data" />
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<link rel="next" href="dplindexcreate.html" title="Creating Indexes" />
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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 4. Working with Indices</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="saveret.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="dplindexcreate.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_index"></a>Chapter 4. Working with Indices</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_index.html#dplindexaccess">Accessing Indexes</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="persist_index.html#primaryindexaccess">Accessing Primary Indices</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="persist_index.html#secondaryindexaccess">Accessing Secondary Indices</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="dplindexcreate.html">Creating Indexes</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="dplindexcreate.html#dplprimaryidxdecl">Declaring Primary Indexes</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="dplindexcreate.html#dplsecondaryidxdecl">Declaring Secondary Indexes</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="dplindexcreate.html#foreignkey">Foreign Key Constraints</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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</dl>
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</div>
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<p>
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All entity classes stored in JE using the DPL must have a
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primary index, or key, identified for them. All such classes may
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also have one or more secondary keys declared for them. This
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chapter describes primary and secondary indexes in detail, and
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shows how to access the indexes created for a given entity class.
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</p>
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<p>
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One way to organize access to your primary and secondary
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indexes is to create a <span class="emphasis"><em>data accessor</em></span>
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class. We show an implementation of a data accessor class in
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<a class="xref" href="simpleda.html" title="SimpleDA.class">SimpleDA.class</a>.
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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="dplindexaccess"></a>Accessing Indexes</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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<dl>
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<dt>
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<span class="sect2">
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<a href="persist_index.html#primaryindexaccess">Accessing Primary Indices</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="persist_index.html#secondaryindexaccess">Accessing Secondary Indices</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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In order to retrieve any object from an entity store, you
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must access at least the primary index for that object.
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Different entity classes stored in an entity store can have
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different primary indexes, but all entity classes must have a
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primary index declared for it. The primary index is just
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the default index used for the class. (That is, it is the
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data's primary <span class="emphasis"><em>key</em></span> for the underlying database.)
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</p>
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<p>
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Entity classes can optionally have secondary indexes
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declared for them. In order to access these secondary
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indexes, you must first access the primary index.
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</p>
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<div class="sect2" 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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<h3 class="title"><a id="primaryindexaccess"></a>Accessing Primary Indices</h3>
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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 retrieve a primary index using the
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<code class="methodname">EntityStore.getPrimaryIndex()</code>
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method. To do this, you indicate the index key type
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(that is, whether it is a String, Integer, and
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so forth) and the class of the entities stored
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in the index.
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</p>
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<p>
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For example, the following retrieves the
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primary index for an <code class="classname">Inventory</code>
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class (we provide an implementation of this class in
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<a class="xref" href="inventoryclass.html" title="Inventory.java">Inventory.java</a>).
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These index keys are of type <code class="classname">String</code>.
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</p>
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<pre class="programlisting">PrimaryIndex<String,Inventory> inventoryBySku =
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store.getPrimaryIndex(String.class, Inventory.class); </pre>
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</div>
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<div class="sect2" 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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<h3 class="title"><a id="secondaryindexaccess"></a>Accessing Secondary Indices</h3>
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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 retrieve a secondary index using the
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<code class="methodname">EntityStore.getSecondaryIndex()</code>
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method. Because secondary indices actually
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refer to a primary index somewhere in your data
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store, to access a secondary index you:
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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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Provide the primary index as
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returned by
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<code class="methodname">EntityStore.getPrimaryIndex()</code>.
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</p>
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</li>
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<li>
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<p>
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Identify the key data type used by
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the secondary index
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(<code class="classname">String</code>,
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<code class="classname">Long</code>,
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and so forth).
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</p>
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</li>
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<li>
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<p>
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Identify the name of the
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secondary key field.
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When you declare the
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<code class="classname">SecondaryIndex</code>
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object, you identify the entity class
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to which the secondary index
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must refer.
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</p>
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</li>
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</ol>
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</div>
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<p>
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For example, the following first retrieves the
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primary index, and then uses that to retrieve a secondary
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index. The secondary key is held by the
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<code class="literal">itemName</code> field of the
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<code class="classname">Inventory</code> class.
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</p>
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<pre class="programlisting">PrimaryIndex<String,Inventory> inventoryBySku =
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store.getPrimaryIndex(String.class, Inventory.class);
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SecondaryIndex<String,String,Inventory> inventoryByName =
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store.getSecondaryIndex(inventoryBySku, String.class, "itemName"); </pre>
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</div>
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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="saveret.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="dpl.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="dplindexcreate.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">Saving and Retrieving Data </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"> Creating Indexes</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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