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		Creating Entity Bindings
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		Creating Entity Bindings
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          <th width="60%" align="center">Chapter 4. 
        Using Entity Classes	
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            <h2 class="title" style="clear: both"><a id="creatingentitybindings"></a>
		Creating Entity Bindings
	</h2>
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        <div></div>
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      <p>
    <span class="emphasis"><em>Entity bindings</em></span> are similar to ordinary bindings in that
	they convert between Java objects and the stored data format of
	keys and values. In addition, entity bindings map between key/value
	pairs and entity objects. An ordinary binding is a one-to-one
	mapping, while an entity binding is a two-to-one mapping.
</p>
      <p>
    The <tt class="literal">partValueBinding</tt>, <tt class="literal">supplierValueBinding</tt> and
	<tt class="literal">shipmentValueBinding</tt> bindings are created below as entity
	bindings rather than (in the prior examples) serial bindings.
</p>
      <a id="entity_sampleviews"></a>
      <pre class="programlisting">import com.sleepycat.bind.EntryBinding;
<b class="userinput"><tt>import com.sleepycat.bind.EntityBinding;</tt></b>
import com.sleepycat.bind.serial.SerialBinding;
<b class="userinput"><tt>import com.sleepycat.bind.serial.SerialSerialBinding;</tt></b>
...

public class SampleViews
{
    ...
    public SampleViews(SampleDatabase db)
    {
        ClassCatalog catalog = db.getClassCatalog();
        SerialBinding partKeyBinding =
            new SerialBinding(catalog, PartKey.class);
<b class="userinput"><tt>        EntityBinding partValueBinding =
            new PartBinding(catalog, PartKey.class, PartData.class);</tt></b>
        SerialBinding supplierKeyBinding =
            new SerialBinding(catalog, SupplierKey.class);
<b class="userinput"><tt>        EntityBinding supplierValueBinding =
            new SupplierBinding(catalog, SupplierKey.class,
                                SupplierData.class);</tt></b>
        SerialBinding shipmentKeyBinding =
            new SerialBinding(catalog, ShipmentKey.class);
<b class="userinput"><tt>        EntityBinding shipmentValueBinding =
            new ShipmentBinding(catalog, ShipmentKey.class,
                                ShipmentData.class);</tt></b>
        SerialBinding cityKeyBinding =
            new SerialBinding(catalog, String.class);
        ...
    }
} </pre>
      <p>
    The entity bindings will be used in the next section to
	construct stored map objects.
</p>
      <p>
    The <tt class="classname">PartBinding</tt> class is defined below.
</p>
      <a id="entity_partbinding"></a>
      <pre class="programlisting">public class SampleViews
{
    ...
<b class="userinput"><tt>    private static class PartBinding extends SerialSerialBinding {
        private PartBinding(ClassCatalog classCatalog,
                            Class keyClass,
                            Class dataClass)
        {
            super(classCatalog, keyClass, dataClass);
        }

public Object entryToObject(Object keyInput, Object dataInput)
        {
            PartKey key = (PartKey) keyInput;
            PartData data = (PartData) dataInput;
            return new Part(key.getNumber(), data.getName(), data.getColor(),
                            data.getWeight(), data.getCity());
        }

public Object objectToKey(Object object)
        {
            Part part = (Part) object;
            return new PartKey(part.getNumber());
        }

public Object objectToData(Object object)
        {
            Part part = (Part) object;
            return new PartData(part.getName(), part.getColor(),
                                 part.getWeight(), part.getCity());
        }
    }</tt></b>
    ...
} </pre>
      <p>
    In general, an entity binding is any class that implements the
	<a href="../../java/com/sleepycat/bind/EntityBinding.html" target="_top">EntityBinding</a>
	
	interface, just as an ordinary binding is any class that implements
	the 
    <a href="../../java/com/sleepycat/bind/EntryBinding.html" target="_top">EntryBinding</a>
    
	interface. In the prior examples the built-in 
    <a href="../../java/com/sleepycat/bind/serial/SerialBinding.html" target="_top">SerialBinding</a>
    
	class (which implements 
    <a href="../../java/com/sleepycat/bind/EntryBinding.html" target="_top">EntryBinding</a>)
	was used and no application-defined binding classes were needed.
</p>
      <p>
    In this example, application-defined binding classes are used
	that extend the 
    <a href="../../java/com/sleepycat/bind/serial/SerialSerialBinding.html" target="_top">SerialSerialBinding</a>
    
	abstract base class. This base class implements 
    <a href="../../java/com/sleepycat/bind/EntityBinding.html" target="_top">EntityBinding</a>
    
	and provides the conversions between key/value bytes and key/value
	objects, just as the 
    <a href="../../java/com/sleepycat/bind/serial/SerialBinding.html" target="_top">SerialBinding</a>
    
	class does. The application-defined entity class implements the
	abstract methods defined in the base class that map between
	key/value objects and entity objects.
</p>
      <p>
    Three abstract methods are implemented for each entity binding.
	The <tt class="methodname">entryToObject()</tt> method takes as input the key and data
	objects, which have been deserialized automatically by the base
	class. As output, it returns the combined <tt class="classname">Part</tt> entity.
</p>
      <p>
    The <tt class="methodname">objectToKey()</tt> and <tt class="methodname">objectToData()</tt> methods take an
	entity object as input. As output they return the part key or data
	object that is extracted from the entity object. The key or data
	will then be serialized automatically by the base class.
</p>
      <p>
    The <tt class="classname">SupplierBinding</tt> and <tt class="classname">ShipmentBinding</tt> classes
	are very similar to the <tt class="classname">PartBinding</tt> class.
</p>
      <a id="entity_supplierbinding"></a>
      <pre class="programlisting">public class SampleViews
{
    ...
<b class="userinput"><tt>    private static class SupplierBinding extends SerialSerialBinding {
        private SupplierBinding(ClassCatalog classCatalog,
                                Class keyClass,
                                Class dataClass)
        {
            super(classCatalog, keyClass, dataClass);
        }

public Object entryToObject(Object keyInput, Object dataInput)
        {
            SupplierKey key = (SupplierKey) keyInput;
            SupplierData data = (SupplierData) dataInput;
            return new Supplier(key.getNumber(), data.getName(),
                                data.getStatus(), data.getCity());
        }

public Object objectToKey(Object object)
        {
            Supplier supplier = (Supplier) object;
            return new SupplierKey(supplier.getNumber());
        }

public Object objectToData(Object object)
        {
            Supplier supplier = (Supplier) object;
            return new SupplierData(supplier.getName(), supplier.getStatus(),
                                     supplier.getCity());
        }
    }

private static class ShipmentBinding extends SerialSerialBinding {
        private ShipmentBinding(ClassCatalog classCatalog,
                                Class keyClass,
                                Class dataClass)
        {
            super(classCatalog, keyClass, dataClass);
        }

public Object entryToObject(Object keyInput, Object dataInput)
        {
            ShipmentKey key = (ShipmentKey) keyInput;
            ShipmentData data = (ShipmentData) dataInput;
            return new Shipment(key.getPartNumber(), key.getSupplierNumber(),
                                data.getQuantity());
        }

public Object objectToKey(Object object)
        {
            Shipment shipment = (Shipment) object;
            return new ShipmentKey(shipment.getPartNumber(),
                                   shipment.getSupplierNumber());
        }

public Object objectToData(Object object)
        {
            Shipment shipment = (Shipment) object;
            return new ShipmentData(shipment.getQuantity());
        }
    }</tt></b>
    ...
} </pre>
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