Edit File: persistobject.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>Persistent Objects</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="Getting Started with Berkeley DB" /> <link rel="up" href="persist_first.html" title="Chapter 3. Direct Persistence Layer First Steps" /> <link rel="previous" href="persist_first.html" title="Chapter 3. Direct Persistence Layer First Steps" /> <link rel="next" href="saveret.html" title="Saving a Retrieving Data" /> </head> <body> <div class="navheader"> <table width="100%" summary="Navigation header"> <tr> <th colspan="3" align="center">Persistent Objects</th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="persist_first.html">Prev</a> </td> <th width="60%" align="center">Chapter 3. Direct Persistence Layer First Steps</th> <td width="20%" align="right"> <a accesskey="n" href="saveret.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="persistobject"></a>Persistent Objects</h2> </div> </div> <div></div> </div> <p> When using the DPL, you store data in the underlying DB databases by making objects <span class="emphasis"><em>persistent</em></span>. You do this using Java annotations that both identify the type of persistent object you are declaring, as well as the primary and secondary indices. </p> <p> The following are the annotations you will use with your DPL persistent classes: </p> <div class="informaltable"> <table border="1" width="80%"> <colgroup> <col /> <col /> </colgroup> <thead> <tr> <th>Annotation</th> <th>Description</th> </tr> </thead> <tbody> <tr> <td>@Entity</td> <td> Declares an entity class; that is, a class with a primary index and optionally one or more indices. </td> </tr> <tr> <td>@Persistent</td> <td> Declares a persistent class; that is, a class used by an entity class. They do not have indices but instead are are stored or retrieved when an entity class makes direct use of them. </td> </tr> <tr> <td>@PrimaryKey</td> <td> Declares a specific data member in an entity class to be the primary key for that object. This annotation must be used one and only one time for every entity class. </td> </tr> <tr> <td>@SecondaryKey</td> <td> Declares a specific data member in an entity class to be a secondary key for that object. This annotation is optional, and can be used multiple times for an entity class. </td> </tr> </tbody> </table> </div> <p> For example, the following is declared to be an entity class: </p> <pre class="programlisting">package persist.gettingStarted; import com.sleepycat.persist.model.Entity; import com.sleepycat.persist.model.PrimaryKey; @Entity public class ExampleEntity { private String aPrimaryKey; private String aSecondaryKey; // The primary key must be unique in the database. @PrimaryKey private String aPrimaryKey; @SecondaryKey(relate=MANY_TO_ONE) private String aSecondaryKey; ... // The remainder of the class' implementation is purposefully // omitted in the interest of brevity. ... } </pre> <p> We discuss primary and secondary keys in more detail in <a href="persist_index.html">Working with Indices</a>. </p> </div> <div class="navfooter"> <hr /> <table width="100%" summary="Navigation footer"> <tr> <td width="40%" align="left"><a accesskey="p" href="persist_first.html">Prev</a> </td> <td width="20%" align="center"> <a accesskey="u" href="persist_first.html">Up</a> </td> <td width="40%" align="right"> <a accesskey="n" href="saveret.html">Next</a></td> </tr> <tr> <td width="40%" align="left" valign="top">Chapter 3. Direct Persistence Layer First Steps </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> Saving a Retrieving Data</td> </tr> </table> </div> </body> </html>
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