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9.2 KiB
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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>Creating Indexed Collections</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="Berkeley DB Java Edition Collections Tutorial" />
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<link rel="up" href="UsingSecondaries.html" title="Chapter 3. Using Secondary Indices and Foreign keys" />
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<link rel="prev" href="openingforeignkeys.html" title="Opening Foreign Key Indices" />
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<link rel="next" href="retrievingbyindexkey.html" title="Retrieving Items by Index Key" />
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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">
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Creating Indexed Collections
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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="openingforeignkeys.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 3.
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Using Secondary Indices<span xmlns="http://www.w3.org/1999/xhtml"> and Foreign keys</span>
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="retrievingbyindexkey.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="indexedcollections"></a>
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Creating Indexed Collections
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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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In the prior Basic example, bindings and Java collections were
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created for accessing databases via their primary keys. In this
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example, bindings and collections are added for accessing the same
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databases via their index keys. As in the prior example, serial
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bindings and the Java
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<a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/util/Map.html" target="_top">Map</a>
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class are used.
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</p>
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<p>
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When a map is created from a
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<span>
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<a class="ulink" href="../../java/com/sleepycat/je/SecondaryDatabase.html" target="_top">SecondaryDatabase</a>,
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</span>
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the keys of the map will be the index keys. However, the values of
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the map will be the values of the primary database associated with
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the index. This is how index keys can be used to access the values
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in a primary database.
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</p>
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<p>
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For example, the Supplier's City field is an index key that can
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be used to access the Supplier database. When a map is created
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using the <code class="methodname">supplierByCityDb()</code> method, the key to the map will be the
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City field, a
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<a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/lang/String.html" target="_top">String</a>
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object. When
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<a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/util/Map.html#get(java.lang.Object)" target="_top">Map.get</a>
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is called passing the City as the key parameter, a
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<code class="classname">SupplierData</code>
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object will be returned.
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</p>
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<p>
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The <code class="classname">SampleViews</code> class is extended to create an index key
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binding for the Supplier's City field and three Java maps based on
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the three indices created in the prior section.
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</p>
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<a id="index_sampleviews"></a>
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<pre class="programlisting">import com.sleepycat.bind.EntryBinding;
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import com.sleepycat.bind.serial.SerialBinding;
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import com.sleepycat.collections.StoredEntrySet;
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import com.sleepycat.collections.StoredSortedMap;
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...
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public class SampleViews
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{
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...
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<strong class="userinput"><code> private StoredSortedMap supplierByCityMap;
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private StoredSortedMap shipmentByPartMap;
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private StoredSortedMap shipmentBySupplierMap;</code></strong>
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...
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public SampleViews(SampleDatabase db)
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{
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ClassCatalog catalog = db.getClassCatalog();
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...
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<strong class="userinput"><code> EntryBinding cityKeyBinding =
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new SerialBinding(catalog, String.class);
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...
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supplierByCityMap =
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new StoredSortedMap(db.getSupplierByCityDatabase(),
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cityKeyBinding, supplierDataBinding, true);
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shipmentByPartMap =
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new StoredSortedMap(db.getShipmentByPartDatabase(),
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partKeyBinding, supplierDataBinding, true);
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shipmentBySupplierMap =
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new StoredSortedMap(db.getShipmentBySupplierDatabase(),
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supplierKeyBinding, supplierDataBinding, true); </code></strong>
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...
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}
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} </pre>
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<p>
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In general, the indexed maps are created here in the same way as
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the unindexed maps were created in the Basic example. The
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differences are:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p>
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The first parameter of the
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<a class="ulink" href="../../java/com/sleepycat/collections/StoredMap.html" target="_top">StoredSortedMap</a>
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constructor is a
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<a class="ulink" href="../../java/com/sleepycat/je/SecondaryDatabase.html" target="_top">SecondaryDatabase</a>
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rather than a
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<span>
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<a class="ulink" href="../../java/com/sleepycat/je/Database.html" target="_top">Database</a>.
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</span>
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</p>
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</li>
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<li>
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<p>
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The second parameter is the index key binding rather than the
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primary key binding.
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</p>
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</li>
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</ul>
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</div>
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<p>
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For the <code class="literal">supplierByCityMap</code>, the <code class="literal">cityKeyBinding</code> must
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first be created. This binding was not created in the Basic example
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because the City field is not a primary key.
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</p>
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<p>
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Like the bindings created earlier for keys and values, the
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<code class="literal">cityKeyBinding</code> is a
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<a class="ulink" href="../../java/com/sleepycat/bind/serial/SerialBinding.html" target="_top">SerialBinding</a>.
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Unlike the bindings created earlier, it is an example of creating a
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binding for a built-in Java class,
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<a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/lang/String.html" target="_top">String</a>,
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instead of an application-defined class. Any serializable class may
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be used.
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</p>
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<p>
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For the <code class="literal">shipmentByPartMap</code> and
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<code class="literal">shipmentBySupplierMap</code>, the <code class="literal">partKeyBinding</code> and
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<code class="literal">supplierKeyBinding</code> are used. These were created in the Basic
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example and used as the primary key bindings for the <code class="literal">partMap</code>
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and <code class="literal">supplierMap</code>.
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</p>
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<p>
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The value bindings — <code class="literal">supplierDataBinding</code> and
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<code class="literal">shipmentDataBinding</code> — were also created in the Basic
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example.
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</p>
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<p>
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This illustrates that bindings and formats may and should be
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reused where appropriate for creating maps and other
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collections.
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</p>
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<p>
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The following getter methods return the stored maps for use by
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other classes in the example program. Convenience methods for
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returning entry sets are also included.
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</p>
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<a id="index_sampleviewsgetters"></a>
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<pre class="programlisting">public class SampleViews
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{
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...
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<strong class="userinput"><code> public final StoredSortedMap getShipmentByPartMap()
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{
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return shipmentByPartMap;
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}
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public final StoredSortedMap getShipmentBySupplierMap()
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{
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return shipmentBySupplierMap;
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}
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public final StoredSortedMap getSupplierByCityMap()
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{
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return supplierByCityMap;
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}
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public final StoredEntrySet getShipmentByPartEntrySet()
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{
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return (StoredEntrySet) shipmentByPartMap.entrySet();
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}
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public final StoredEntrySet getShipmentBySupplierEntrySet()
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{
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return (StoredEntrySet) shipmentBySupplierMap.entrySet();
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}
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public final StoredEntrySet getSupplierByCityEntrySet()
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{
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return (StoredEntrySet) supplierByCityMap.entrySet();
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}</code></strong>
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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="openingforeignkeys.html">Prev</a> </td>
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||
<td width="20%" align="center">
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<a accesskey="u" href="UsingSecondaries.html">Up</a>
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</td>
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||
<td width="40%" align="right"> <a accesskey="n" href="retrievingbyindexkey.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">
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<span>Opening Foreign Key Indices</span>
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|
||
</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>
|
||
<td width="40%" align="right" valign="top">
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Retrieving Items by Index Key
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</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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