<!--$Id: tbinding.html,v 1.2 2004/03/30 01:22:47 jtownsen Exp $--> <!--Copyright 1997-2003 by Sleepycat Software, Inc.--> <!--All rights reserved.--> <!--See the file LICENSE for redistribution information.--> <html> <head> <title>Berkeley DB Reference Guide: Tuple - Creating tuple key bindings</title> <meta name="description" content="Berkeley DB: An embedded database programmatic toolkit."> <meta name="keywords" content="embedded,database,programmatic,toolkit,b+tree,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++"> </head> <body bgcolor=white> <a name="2"><!--meow--></a> <table width="100%"><tr valign=top> <td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Java API Tutorial - Tuple</dl></h3></td> <td align=right><a href="../bdb_tuple/extract.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../toc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../bdb_tuple/tsbinding.html"><img src="../../images/next.gif" alt="Next"></a> </td></tr></table> <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> <table width="100%"><tr><td><br></td><td align=right><a href="../bdb_tuple/extract.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../toc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../bdb_tuple/tsbinding.html"><img src="../../images/next.gif" alt="Next"></a> </td></tr></table> <p><font size=1><a href="../../sleepycat/legal.html">Copyright (c) 1996-2003</a> <a href="http://www.sleepycat.com">Sleepycat Software, Inc.</a> - All rights reserved.</font> </body> </html>