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272 lines
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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 Entity Bindings</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="Entity.html" title="Chapter 4. Using Entity Classes" />
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<link rel="prev" href="Entity.html" title="Chapter 4. Using Entity Classes" />
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<link rel="next" href="collectionswithentities.html" title="Creating Collections with Entity Bindings" />
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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 Entity Bindings
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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="Entity.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 4.
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Using Entity Classes
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="collectionswithentities.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="creatingentitybindings"></a>
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Creating Entity Bindings
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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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<span class="emphasis"><em>Entity bindings</em></span> are similar to ordinary bindings in that
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they convert between Java objects and the stored data format of
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keys and values. In addition, entity bindings map between key/value
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pairs and entity objects. An ordinary binding is a one-to-one
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mapping, while an entity binding is a two-to-one mapping.
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</p>
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<p>
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The <code class="literal">partDataBinding</code>, <code class="literal">supplierDataBinding</code> and
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<code class="literal">shipmentDataBinding</code> bindings are created below as entity
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bindings rather than (in the prior examples) serial bindings.
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</p>
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<a id="entity_sampleviews"></a>
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<pre class="programlisting">import com.sleepycat.bind.EntryBinding;
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<strong class="userinput"><code>import com.sleepycat.bind.EntityBinding;</code></strong>
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import com.sleepycat.bind.serial.SerialBinding;
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<strong class="userinput"><code>import com.sleepycat.bind.serial.SerialSerialBinding;</code></strong>
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...
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public class SampleViews
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{
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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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SerialBinding partKeyBinding =
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new SerialBinding(catalog, PartKey.class);
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<strong class="userinput"><code> EntityBinding partDataBinding =
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new PartBinding(catalog, PartKey.class, PartData.class);</code></strong>
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SerialBinding supplierKeyBinding =
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new SerialBinding(catalog, SupplierKey.class);
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<strong class="userinput"><code> EntityBinding supplierDataBinding =
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new SupplierBinding(catalog, SupplierKey.class,
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SupplierData.class);</code></strong>
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SerialBinding shipmentKeyBinding =
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new SerialBinding(catalog, ShipmentKey.class);
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<strong class="userinput"><code> EntityBinding shipmentDataBinding =
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new ShipmentBinding(catalog, ShipmentKey.class,
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ShipmentData.class);</code></strong>
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SerialBinding cityKeyBinding =
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new SerialBinding(catalog, String.class);
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...
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}
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} </pre>
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<p>
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The entity bindings will be used in the next section to
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construct stored map objects.
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</p>
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<p>
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The <code class="classname">PartBinding</code> class is defined below.
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</p>
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<a id="entity_partbinding"></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> private static class PartBinding extends SerialSerialBinding {
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private PartBinding(ClassCatalog classCatalog,
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Class keyClass,
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Class dataClass)
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{
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super(classCatalog, keyClass, dataClass);
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}
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public Object entryToObject(Object keyInput, Object dataInput)
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{
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PartKey key = (PartKey) keyInput;
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PartData data = (PartData) dataInput;
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return new Part(key.getNumber(), data.getName(),
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data.getColor(), data.getWeight(),
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data.getCity());
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}
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public Object objectToKey(Object object)
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{
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Part part = (Part) object;
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return new PartKey(part.getNumber());
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}
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public Object objectToData(Object object)
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{
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Part part = (Part) object;
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return new PartData(part.getName(), part.getColor(),
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part.getWeight(), part.getCity());
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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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In general, an entity binding is any class that implements the
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<a class="ulink" href="../../java/com/sleepycat/bind/EntityBinding.html" target="_top">EntityBinding</a>
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interface, just as an ordinary binding is any class that implements
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the
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<a class="ulink" href="../../java/com/sleepycat/bind/EntryBinding.html" target="_top">EntryBinding</a>
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interface. In the prior examples the built-in
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<a class="ulink" href="../../java/com/sleepycat/bind/serial/SerialBinding.html" target="_top">SerialBinding</a>
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class (which implements
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<a class="ulink" href="../../java/com/sleepycat/bind/EntryBinding.html" target="_top">EntryBinding</a>)
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was used and no application-defined binding classes were needed.
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</p>
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<p>
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In this example, application-defined binding classes are used
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that extend the
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<a class="ulink" href="../../java/com/sleepycat/bind/serial/SerialSerialBinding.html" target="_top">SerialSerialBinding</a>
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abstract base class. This base class implements
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<a class="ulink" href="../../java/com/sleepycat/bind/EntityBinding.html" target="_top">EntityBinding</a>
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and provides the conversions between key/value bytes and key/value
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objects, just as the
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<a class="ulink" href="../../java/com/sleepycat/bind/serial/SerialBinding.html" target="_top">SerialBinding</a>
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class does. The application-defined entity class implements the
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abstract methods defined in the base class that map between
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key/value objects and entity objects.
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</p>
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<p>
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Three abstract methods are implemented for each entity binding.
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The <code class="methodname">entryToObject()</code> method takes as input the key and data
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objects, which have been deserialized automatically by the base
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class. As output, it returns the combined <code class="classname">Part</code> entity.
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</p>
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<p>
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The <code class="methodname">objectToKey()</code> and <code class="methodname">objectToData()</code> methods take an
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entity object as input. As output they return the part key or data
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object that is extracted from the entity object. The key or data
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will then be serialized automatically by the base class.
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</p>
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<p>
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The <code class="classname">SupplierBinding</code> and <code class="classname">ShipmentBinding</code> classes
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are very similar to the <code class="classname">PartBinding</code> class.
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</p>
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<a id="entity_supplierbinding"></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> private static class SupplierBinding extends SerialSerialBinding {
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private SupplierBinding(ClassCatalog classCatalog,
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Class keyClass,
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Class dataClass)
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{
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super(classCatalog, keyClass, dataClass);
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}
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public Object entryToObject(Object keyInput, Object dataInput)
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{
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SupplierKey key = (SupplierKey) keyInput;
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SupplierData data = (SupplierData) dataInput;
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return new Supplier(key.getNumber(), data.getName(),
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data.getStatus(), data.getCity());
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}
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public Object objectToKey(Object object)
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{
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Supplier supplier = (Supplier) object;
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return new SupplierKey(supplier.getNumber());
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}
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public Object objectToData(Object object)
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{
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Supplier supplier = (Supplier) object;
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return new SupplierData(supplier.getName(),
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supplier.getStatus(),
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supplier.getCity());
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}
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}
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private static class ShipmentBinding extends SerialSerialBinding {
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private ShipmentBinding(ClassCatalog classCatalog,
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Class keyClass,
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Class dataClass)
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{
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super(classCatalog, keyClass, dataClass);
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}
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public Object entryToObject(Object keyInput, Object dataInput)
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{
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ShipmentKey key = (ShipmentKey) keyInput;
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ShipmentData data = (ShipmentData) dataInput;
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return new Shipment(key.getPartNumber(),
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key.getSupplierNumber(),
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data.getQuantity());
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}
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public Object objectToKey(Object object)
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{
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Shipment shipment = (Shipment) object;
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return new ShipmentKey(shipment.getPartNumber(),
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shipment.getSupplierNumber());
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}
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public Object objectToData(Object object)
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{
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Shipment shipment = (Shipment) object;
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return new ShipmentData(shipment.getQuantity());
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}
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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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|||
|
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<table width="100%" summary="Navigation footer">
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|||
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<tr>
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|||
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<td width="40%" align="left"><a accesskey="p" href="Entity.html">Prev</a> </td>
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|||
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<td width="20%" align="center">
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|||
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<a accesskey="u" href="Entity.html">Up</a>
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|||
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</td>
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|||
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<td width="40%" align="right"> <a accesskey="n" href="collectionswithentities.html">Next</a></td>
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|||
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</tr>
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|||
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<tr>
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<td width="40%" align="left" valign="top">Chapter 4.
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|||
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Using Entity Classes
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|||
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</td>
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<td width="20%" align="center">
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|||
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<a accesskey="h" href="index.html">Home</a>
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|||
|
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</td>
|
|||
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<td width="40%" align="right" valign="top">
|
|||
|
|
Creating Collections with Entity Bindings
|
|||
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</td>
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|||
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</tr>
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|||
|
|
</table>
|
|||
|
|
</div>
|
|||
|
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</body>
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|||
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</html>
|