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Using Tuples with Key Creators
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<h2 class="title" style="clear: both"><a id="tupleswithkeycreators"></a>
Using Tuples with Key Creators
</h2>
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<p>
Key creators were used in prior examples to extract index keys
from value objects. The keys were returned as deserialized key
objects, since the serial format was used for keys. In this
example, the tuple format is used for keys and the key creators
return keys by writing information to a tuple. The differences
between this example and the prior example are:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
The
<a class="ulink" href="../../java/com/sleepycat/bind/serial/TupleSerialKeyCreator.html" target="_top">TupleSerialKeyCreator</a>
base class is used instead of the
<a class="ulink" href="../../java/com/sleepycat/bind/serial/SerialSerialKeyCreator.html" target="_top">SerialSerialKeyCreator</a>
base class.
</p>
</li>
<li>
<p>
For all key input and output parameters, the
<a class="ulink" href="../../java/com/sleepycat/bind/tuple/TupleInput.html" target="_top">TupleInput</a>
and
<a class="ulink" href="../../java/com/sleepycat/bind/tuple/TupleOutput.html" target="_top">TupleOutput</a>
classes are used instead of
<a class="ulink" href="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Object.html" target="_top">Object</a>
(representing a deserialized object).
</p>
</li>
<li>
<p>
Instead of returning a key output object, these methods call
tuple write methods such as
<a class="ulink" href="../../java/com/sleepycat/bind/tuple/TupleOutput.html#writeString(java.lang.String)" target="_top">TupleOutput.writeString</a>.
</p>
</li>
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<p>
In addition to writing key tuples, the
<code class="classname">ShipmentByPartKeyCreator</code> and
<code class="classname">ShipmentBySupplierKeyCreator</code> classes also read the key tuple
of the primary key. This is because they extract the index key from
fields in the Shipment's primary key. Instead of calling getter
methods on the <code class="classname">ShipmentKey</code> object, as in prior examples,
these methods call
<a class="ulink" href="../../java/com/sleepycat/bind/tuple/TupleInput.html#readString()" target="_top">TupleInput.readString</a>.
The <code class="classname">ShipmentKey</code> consists of two string fields that are read
in sequence.
</p>
<p>
The modified key creators are shown below:
<code class="classname">SupplierByCityKeyCreator</code>,
<code class="classname">ShipmentByPartKeyCreator</code>
and <code class="classname">ShipmentBySupplierKeyCreator</code>.
</p>
<a id="tuple_SupplierByCityKeyCreator"></a>
<pre class="programlisting"><strong class="userinput"><code>import com.sleepycat.bind.serial.TupleSerialKeyCreator;
import com.sleepycat.bind.tuple.TupleInput;
import com.sleepycat.bind.tuple.TupleOutput;
...</code></strong>
public class SampleDatabase
{
...
private static class SupplierByCityKeyCreator
<strong class="userinput"><code> extends TupleSerialKeyCreator</code></strong>
{
private SupplierByCityKeyCreator(ClassCatalog catalog,
<strong class="userinput"><code>Class valueClass</code></strong>)
{
super(catalog, valueClass);
}
<strong class="userinput"><code> public boolean createSecondaryKey(TupleInput primaryKeyInput,
Object valueInput,
TupleOutput indexKeyOutput)
{
SupplierData supplierData = (SupplierData) valueInput;
String city = supplierData.getCity();
if (city != null) {
indexKeyOutput.writeString(supplierData.getCity());
return true;
} else {
return false;
}
}</code></strong>
}
private static class ShipmentByPartKeyCreator
<strong class="userinput"><code>extends TupleSerialKeyCreator</code></strong>
{
private ShipmentByPartKeyCreator(ClassCatalog catalog,
<strong class="userinput"><code>Class valueClass</code></strong>)
{
super(catalog, valueClass);
}
<strong class="userinput"><code>public boolean createSecondaryKey(TupleInput primaryKeyInput,
Object valueInput,
TupleOutput indexKeyOutput)
{
String partNumber = primaryKeyInput.readString();
// don't bother reading the supplierNumber
indexKeyOutput.writeString(partNumber);
return true;
}</code></strong>
}
private static class ShipmentBySupplierKeyCreator
<strong class="userinput"><code>extends TupleSerialKeyCreator</code></strong>
{
private ShipmentBySupplierKeyCreator(ClassCatalog catalog,
<strong class="userinput"><code>Class valueClass</code></strong>)
{
super(catalog, valueClass);
}
<strong class="userinput"><code>public boolean createSecondaryKey(TupleInput primaryKeyInput,
Object valueInput,
TupleOutput indexKeyOutput)
{
primaryKeyInput.readString(); // skip the partNumber
String supplierNumber = primaryKeyInput.readString();
indexKeyOutput.writeString(supplierNumber);
return true;
}</code></strong>
}
...
}
</pre>
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