Edit File: tupleswithkeycreators.html
<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> <title> Using Tuples with Key Creators </title> <link rel="stylesheet" href="gettingStarted.css" type="text/css" /> <meta name="generator" content="DocBook XSL Stylesheets V1.62.4" /> <link rel="home" href="index.html" title="Berkeley DB Collections Tutorial" /> <link rel="up" href="Tuple.html" title="Chapter 5. 		Using Tuples 	" /> <link rel="previous" href="Tuple.html" title="Chapter 5. 		Using Tuples 	" /> <link rel="next" href="tuplekeybindings.html" title=" 		Creating Tuple Key Bindings 	" /> </head> <body> <div class="navheader"> <table width="100%" summary="Navigation header"> <tr> <th colspan="3" align="center"> Using Tuples with Key Creators </th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="Tuple.html">Prev</a> </td> <th width="60%" align="center">Chapter 5. Using Tuples </th> <td width="20%" align="right"> <a accesskey="n" href="tuplekeybindings.html">Next</a></td> </tr> </table> <hr /> </div> <div class="sect1" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h2 class="title" style="clear: both"><a id="tupleswithkeycreators"></a> Using Tuples with Key Creators </h2> </div> </div> <div></div> </div> <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 href="../../java/com/sleepycat/bind/serial/TupleSerialKeyCreator.html" target="_top">TupleSerialKeyCreator</a> base class is used instead of the <a 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 href="../../java/com/sleepycat/bind/tuple/TupleInput.html" target="_top">TupleInput</a> and <a href="../../java/com/sleepycat/bind/tuple/TupleOutput.html" target="_top">TupleOutput</a> classes are used instead of <a 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 href="../../java/com/sleepycat/bind/tuple/TupleOutput.html#writeString(java.lang.String)" target="_top">TupleOutput.writeString</a>. </p> </li> </ul> </div> <p> In addition to writing key tuples, the <tt class="classname">ShipmentByPartKeyCreator</tt> and <tt class="classname">ShipmentBySupplierKeyCreator</tt> 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 <tt class="classname">ShipmentKey</tt> object, as in prior examples, these methods call <a href="../../java/com/sleepycat/bind/tuple/TupleInput.html#readString()" target="_top">TupleInput.readString</a>. The <tt class="classname">ShipmentKey</tt> consists of two string fields that are read in sequence. </p> <p> The modified key creators are shown below: <tt class="classname">SupplierByCityKeyCreator</tt>, <tt class="classname">ShipmentByPartKeyCreator</tt> and <tt class="classname">ShipmentBySupplierKeyCreator</tt>. </p> <a id="tuple_SupplierByCityKeyCreator"></a> <pre class="programlisting"><b class="userinput"><tt>import com.sleepycat.bind.serial.TupleSerialKeyCreator; import com.sleepycat.bind.tuple.TupleInput; import com.sleepycat.bind.tuple.TupleOutput; ...</tt></b> public class SampleDatabase { ... private static class SupplierByCityKeyCreator <b class="userinput"><tt> extends TupleSerialKeyCreator</tt></b> { private SupplierByCityKeyCreator(StoredClassCatalog catalog, <b class="userinput"><tt>Class valueClass</tt></b>) { super(catalog, valueClass); } <b class="userinput"><tt> 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; } }</tt></b> } private static class ShipmentByPartKeyCreator <b class="userinput"><tt>extends TupleSerialKeyCreator</tt></b> { private ShipmentByPartKeyCreator(StoredClassCatalog catalog, <b class="userinput"><tt>Class valueClass</tt></b>) { super(catalog, valueClass); } <b class="userinput"><tt>public boolean createSecondaryKey(TupleInput primaryKeyInput, Object valueInput, TupleOutput indexKeyOutput) { String partNumber = primaryKeyInput.readString(); // don't bother reading the supplierNumber indexKeyOutput.writeString(partNumber); return true; }</tt></b> } private static class ShipmentBySupplierKeyCreator <b class="userinput"><tt>extends TupleSerialKeyCreator</tt></b> { private ShipmentBySupplierKeyCreator(StoredClassCatalog catalog, <b class="userinput"><tt>Class valueClass</tt></b>) { super(catalog, valueClass); } <b class="userinput"><tt>public boolean createSecondaryKey(TupleInput primaryKeyInput, Object valueInput, TupleOutput indexKeyOutput) { primaryKeyInput.readString(); // skip the partNumber String supplierNumber = primaryKeyInput.readString(); indexKeyOutput.writeString(supplierNumber); return true; }</tt></b> } ... } </pre> </div> <div class="navfooter"> <hr /> <table width="100%" summary="Navigation footer"> <tr> <td width="40%" align="left"><a accesskey="p" href="Tuple.html">Prev</a> </td> <td width="20%" align="center"> <a accesskey="u" href="Tuple.html">Up</a> </td> <td width="40%" align="right"> <a accesskey="n" href="tuplekeybindings.html">Next</a></td> </tr> <tr> <td width="40%" align="left" valign="top">Chapter 5. Using Tuples </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> Creating Tuple Key Bindings </td> </tr> </table> </div> </body> </html>
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