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<title>Berkeley DB Reference Guide: Tuple - Creating tuple key bindings</title>
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<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Java API Tutorial - Tuple</dl></h3></td>
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<p>
<h3 align=center>Tuple - Creating tuple key bindings</h3>
<p>Serial bindings were used in prior examples as key bindings, and keys
were stored as serialized objects.  In this example, a tuple binding is used
for each key since keys will be stored as tuples.  Because keys are no
longer stored as serialized objects, the <b>PartKey</b>,
<b>SupplierKey</b> and <b>ShipmentKey</b> classes no longer implement the
<a href="http://java.sun.com/j2se/1.3/docs/api/java/io/Serializable.html">Serializable</a>
 interface (this was the only change to
these classes and is not shown below).</p>
<hr size=1 noshade>
<p>For the Part key, Supplier key, and Shipment key, the
<b>SampleViews</b> class was changed in this example to create a custom
<a href="../../java/com/sleepycat/bdb/bind/tuple/TupleBinding.html">TupleBinding</a>
 instead of a
<a href="../../java/com/sleepycat/bdb/bind/serial/SerialBinding.html">SerialBinding</a>
.  The custom
tuple key binding classes are defined further below.</p>
<blockquote><pre>
<b>import com.sleepycat.bdb.bind.tuple.TupleBinding;
...
</b>public class SampleViews
{
    ...
    public SampleViews(SampleDatabase db)
    {
        DataBinding partKeyBinding =
<b>            new PartKeyBinding(db.getPartKeyFormat());
</b>        EntityBinding partValueBinding =
            new PartBinding(db.getPartKeyFormat(), db.getPartValueFormat());
        DataBinding supplierKeyBinding =
<b>            new SupplierKeyBinding(db.getSupplierKeyFormat());
</b>        EntityBinding supplierValueBinding =
            new SupplierBinding(db.getSupplierKeyFormat(),
                                db.getSupplierValueFormat());
        DataBinding shipmentKeyBinding =
<b>            new ShipmentKeyBinding(db.getShipmentKeyFormat());
</b>        EntityBinding shipmentValueBinding =
            new ShipmentBinding(db.getShipmentKeyFormat(),
                                db.getShipmentValueFormat());
        DataBinding cityKeyBinding =
<b>            TupleBinding.getPrimitiveBinding(String.class,
                                             db.getCityKeyFormat());
        ...
</b>    }
}
</pre></blockquote>
<p>For the City key, however, a custom binding class is not needed because
the key class is a primitive Java type, 
<a href="http://java.sun.com/j2se/1.3/docs/api/java/lang/String.html">String</a>
.
For any primitive Java type, a tuple binding may be created using the
<a href="../../java/com/sleepycat/bdb/bind/tuple/TupleBinding.html#getPrimitiveBinding">TupleBinding.getPrimitiveBinding</a>
static method.</p>
<hr size=1 noshade>
<p>The custom key binding classes, <b>PartKeyBinding</b>,
<b>SupplierKeyBinding</b> and <b>ShipmentKeyBinding</b>, are defined by
extending the 
<a href="../../java/com/sleepycat/bdb/bind/tuple/TupleBinding.html">TupleBinding</a>
 class.
The 
<a href="../../java/com/sleepycat/bdb/bind/tuple/TupleBinding.html">TupleBinding</a>
 abstract class
implements the 
<a href="../../java/com/sleepycat/bdb/bind/DataBinding.html">DataBinding</a>
 interface, and
is used for one-to-one bindings between tuples and objects.  Each binding
class implements two methods for converting between tuples and objects.  Tuple
fields are read using the 
<a href="../../java/com/sleepycat/bdb/bind/tuple/TupleInput.html">TupleInput</a>
parameter and written using the 
<a href="../../java/com/sleepycat/bdb/bind/tuple/TupleOutput.html">TupleOutput</a>
 parameter.</p>
<blockquote><pre>
<b>
import com.sleepycat.bdb.bind.tuple.TupleBinding;
import com.sleepycat.bdb.bind.tuple.TupleFormat;
import com.sleepycat.bdb.bind.tuple.TupleInput;
import com.sleepycat.bdb.bind.tuple.TupleOutput;
...
</b>public class SampleViews
{
    ...
<b>
    private static class PartKeyBinding extends TupleBinding
    {
        private PartKeyBinding(TupleFormat format)
        {
            super(format);
        }
<p>
        public Object dataToObject(TupleInput input)
            throws IOException
        {
            String number = input.readString();
            return new PartKey(number);
        }
<p>
        public void objectToData(Object object, TupleOutput output)
            throws IOException
        {
            PartKey key = (PartKey) object;
            output.writeString(key.getNumber());
        }
    }
    ...
    private static class SupplierKeyBinding extends TupleBinding
    {
        private SupplierKeyBinding(TupleFormat format)
        {
            super(format);
        }
<p>
        public Object dataToObject(TupleInput input)
            throws IOException
        {
            String number = input.readString();
            return new SupplierKey(number);
        }
<p>
        public void objectToData(Object object, TupleOutput output)
            throws IOException
        {
            SupplierKey key = (SupplierKey) object;
            output.writeString(key.getNumber());
        }
    }
    ...
    private static class ShipmentKeyBinding extends TupleBinding
    {
        private ShipmentKeyBinding(TupleFormat format)
        {
            super(format);
        }
<p>
        public Object dataToObject(TupleInput input)
            throws IOException
        {
            String partNumber = input.readString();
            String supplierNumber = input.readString();
            return new ShipmentKey(partNumber, supplierNumber);
        }
<p>
        public void objectToData(Object object, TupleOutput output)
            throws IOException
        {
            ShipmentKey key = (ShipmentKey) object;
            output.writeString(key.getPartNumber());
            output.writeString(key.getSupplierNumber());
        }
    }
</b>}
</pre></blockquote>
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