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<title>Retrieving Items by Index Key</title>
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<link rel="start" href="index.html" title="Berkeley DB Collections Tutorial" />
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<link rel="up" href="UsingSecondaries.html" title="Chapter 3. Using Secondary Indices" />
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<link rel="prev" href="indexedcollections.html" title="Creating Indexed Collections" />
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<link rel="next" href="Entity.html" title="Chapter 4. Using Entity Classes" />
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 11.2.5.2</p>
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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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Retrieving Items by Index Key
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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="indexedcollections.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 3.
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Using Secondary Indices
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="Entity.html">Next</a></td>
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</table>
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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="retrievingbyindexkey"></a>
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Retrieving Items by Index Key
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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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Retrieving information via database index keys can be
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accomplished using the standard Java collections API, using a
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collection created from a
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<a class="ulink" href="../../java/com/sleepycat/db/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/db/Database.html" target="_top">Database</a>.
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</span>
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However, the standard Java API does not support <span class="emphasis"><em>duplicate keys</em></span>: more
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than one element in a collection having the same key. All three
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indices created in the prior section have duplicate keys because of
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the nature of the city, part number and supplier number index keys.
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More than one supplier may be in the same city, and more than one
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shipment may have the same part number or supplier number. This
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section describes how to use extended methods for stored
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collections to return all values for a given key.
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</p>
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<p>
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Using the standard Java collections API, the
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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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method for a stored collection with duplicate keys will return only
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the first value for a given key. To obtain all values for a given
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key, the
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<a class="ulink" href="../../java/com/sleepycat/collections/StoredMap.html#duplicates(java.lang.Object)" target="_top">StoredMap.duplicates</a>
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method may be called. This returns a
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<a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/util/Collection.html" target="_top">Collection</a>
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of values for the given key. If duplicate keys are not allowed, the
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returned collection will have at most one value. If the key is not
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present in the map, an empty collection is returned.
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</p>
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<p>
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The <code class="classname">Sample</code> class is extended to retrieve duplicates for
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specific index keys that are present in the database.
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</p>
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<a id="index_sampleviewsprintdatabase"></a>
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<pre class="programlisting">import java.util.Iterator;
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...
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public class Sample
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{
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...
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private SampleViews views;
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...
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private class PrintDatabase implements TransactionWorker
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{
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public void doWork()
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throws Exception
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{
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printEntries("Parts",
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views.getPartEntrySet().iterator());
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printEntries("Suppliers",
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views.getSupplierEntrySet().iterator());
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<strong class="userinput"><code> printValues("Suppliers for City Paris",
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views.getSupplierByCityMap().duplicates(
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"Paris").iterator());</code></strong>
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printEntries("Shipments",
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views.getShipmentEntrySet().iterator());
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<strong class="userinput"><code> printValues("Shipments for Part P1",
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views.getShipmentByPartMap().duplicates(
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new PartKey("P1")).iterator());
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printValues("Shipments for Supplier S1",
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views.getShipmentBySupplierMap().duplicates(
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new
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SupplierKey("S1")).iterator());</code></strong>
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}
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}
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<strong class="userinput"><code> private void printValues(String label, Iterator iterator)
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{
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System.out.println("\n--- " + label + " ---");
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while (iterator.hasNext())
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{
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System.out.println(iterator.next().toString());
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}
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} </code></strong>
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...
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} </pre>
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<p>
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The
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<a class="ulink" href="../../java/com/sleepycat/collections/StoredMap.html#duplicates(java.lang.Object)" target="_top">StoredMap.duplicates</a>
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method is called passing the desired key. The returned value is a
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standard Java
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<a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/util/Collection.html" target="_top">Collection</a>
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containing the values for the specified key. A standard Java
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<a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/util/Iterator.html" target="_top">Iterator</a>
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is then obtained for this collection and all values returned by
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that iterator are printed.
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</p>
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<p>
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Another technique for retrieving duplicates is to use the
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collection returned by
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<a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/util/Map.html#entrySet()" target="_top">Map.entrySet</a>.
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When duplicate keys are present, a
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<a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/util/Map.Entry.html" target="_top">Map.Entry</a>
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object will be present in this collection for each duplicate. This
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collection can then be iterated or a subset can be created from it,
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all using the standard Java collection API.
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</p>
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<p>
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Note that we did not discuss how duplicates keys can be
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explicitly added or removed in a collection. For index keys, the
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addition and deletion of duplicate keys happens automatically when
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records containing the index key are added, updated, or
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removed.
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</p>
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<p>
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While not shown in the example program, it is also possible to
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create a store with duplicate keys in the same way as an index with
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duplicate keys — by calling
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<code class="methodname">DatabaseConfig.setSortedDuplicates()</code> method. In that case,
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calling
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<a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/util/Map.html#put(K, V)" target="_top">Map.put</a>
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will add duplicate keys. To remove all duplicate keys, call
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<a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/util/Map.html#remove(java.lang.Object)" target="_top">Map.remove</a>.
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To remove a specific duplicate key, call
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<a class="ulink" href="../../java/com/sleepycat/collections/StoredMap.html#duplicates(java.lang.Object)" target="_top">StoredMap.duplicates</a>
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and then call
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<a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/util/Collection.html#remove(java.lang.Object)" target="_top">Collection.remove</a>
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using the returned collection. Duplicate
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values may also be added to this collection using
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<a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/util/Collection.html#add(E)" target="_top"> Collection.add</a>.
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</p>
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<p>
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The output of the example program is shown below.
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</p>
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<pre class="programlisting">Adding Suppliers
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Adding Parts
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Adding Shipments
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--- Parts ---
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PartKey: number=P1
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PartData: name=Nut color=Red weight=[12.0 grams] city=London
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PartKey: number=P2
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PartData: name=Bolt color=Green weight=[17.0 grams] city=Paris
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PartKey: number=P3
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PartData: name=Screw color=Blue weight=[17.0 grams] city=Rome
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PartKey: number=P4
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PartData: name=Screw color=Red weight=[14.0 grams] city=London
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PartKey: number=P5
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PartData: name=Cam color=Blue weight=[12.0 grams] city=Paris
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PartKey: number=P6
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PartData: name=Cog color=Red weight=[19.0 grams] city=London
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--- Suppliers ---
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SupplierKey: number=S1
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SupplierData: name=Smith status=20 city=London
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SupplierKey: number=S2
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SupplierData: name=Jones status=10 city=Paris
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SupplierKey: number=S3
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SupplierData: name=Blake status=30 city=Paris
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SupplierKey: number=S4
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SupplierData: name=Clark status=20 city=London
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SupplierKey: number=S5
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SupplierData: name=Adams status=30 city=Athens
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<strong class="userinput"><code>--- Suppliers for City Paris ---
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SupplierData: name=Jones status=10 city=Paris
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SupplierData: name=Blake status=30 city=Paris</code></strong>
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--- Shipments ---
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ShipmentKey: supplier=S1 part=P1
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ShipmentData: quantity=300
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ShipmentKey: supplier=S2 part=P1
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ShipmentData: quantity=300
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ShipmentKey: supplier=S1 part=P2
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ShipmentData: quantity=200
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ShipmentKey: supplier=S2 part=P2
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ShipmentData: quantity=400
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ShipmentKey: supplier=S3 part=P2
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ShipmentData: quantity=200
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ShipmentKey: supplier=S4 part=P2
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ShipmentData: quantity=200
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ShipmentKey: supplier=S1 part=P3
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ShipmentData: quantity=400
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ShipmentKey: supplier=S1 part=P4
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ShipmentData: quantity=200
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ShipmentKey: supplier=S4 part=P4
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ShipmentData: quantity=300
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ShipmentKey: supplier=S1 part=P5
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ShipmentData: quantity=100
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ShipmentKey: supplier=S4 part=P5
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ShipmentData: quantity=400
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ShipmentKey: supplier=S1 part=P6
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ShipmentData: quantity=100 <strong class="userinput"><code>
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--- Shipments for Part P1 ---
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ShipmentData: quantity=300
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ShipmentData: quantity=300
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--- Shipments for Supplier S1 ---
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ShipmentData: quantity=300
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ShipmentData: quantity=200
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ShipmentData: quantity=400
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ShipmentData: quantity=200
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ShipmentData: quantity=100
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ShipmentData: quantity=100</code></strong> </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="indexedcollections.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="Entity.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 Indexed Collections
|
|||
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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>
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<td width="40%" align="right" valign="top"> Chapter 4.
|
|||
|
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Using Entity Classes
|
|||
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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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