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170 lines
6.4 KiB
HTML
170 lines
6.4 KiB
HTML
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Retrieving Objects from an Entity Store</title>
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<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Getting Started with Berkeley DB Java Edition" />
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<link rel="up" href="persist_access.html" title="Chapter 5. Saving and Retrieving Objects" />
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<link rel="prev" href="simpleput.html" title="Placing Objects in an Entity Store" />
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<link rel="next" href="getmultiple.html" title="Retrieving Multiple Objects" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 12.2.7.5</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Retrieving Objects from an Entity Store</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="simpleput.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 5. Saving and Retrieving Objects</th>
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<td width="20%" align="right"> <a accesskey="n" href="getmultiple.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="simpleget"></a>Retrieving Objects from an Entity Store</h2>
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</div>
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</div>
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</div>
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<p>
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You retrieve objects placed in an entity store by using
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either the object's primary index, or the appropriate
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secondary index if it exists. The following application
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illustrates this by retrieving some of the objects that
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we placed in an entity store in the previous section.
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</p>
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<p>
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To begin, we import the Java classes that our example
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needs. We also instantiate the private data members that we
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require.
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</p>
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<pre class="programlisting">package persist.gettingStarted;
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import java.io.File;
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import com.sleepycat.je.DatabaseException;
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import com.sleepycat.je.Environment;
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import com.sleepycat.je.EnvironmentConfig;
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import com.sleepycat.persist.EntityStore;
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import com.sleepycat.persist.StoreConfig;
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public class SimpleStoreGet {
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private static File envHome = new File("./JEDB");
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private Environment envmnt;
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private EntityStore store;
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private SimpleDA sda; </pre>
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<p>
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Next we create a method that simply opens our database
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environment and entity store for us.
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</p>
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<pre class="programlisting"> // The setup() method opens the environment and store
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// for us.
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public void setup()
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throws DatabaseException {
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EnvironmentConfig envConfig = new EnvironmentConfig();
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StoreConfig storeConfig = new StoreConfig();
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envConfig.setAllowCreate(true);
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storeConfig.setAllowCreate(true);
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// Open the environment and entity store
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envmnt = new Environment(envHome, envConfig);
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store = new EntityStore(envmnt, "EntityStore", storeConfig);
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} </pre>
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<p>
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We also need a method to close our environment and store.
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</p>
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<pre class="programlisting"> // Close our environment and store.
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public void shutdown()
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throws DatabaseException {
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store.close();
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envmnt.close();
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} </pre>
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<p>
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Now we retrieve a few objects. To do this, we instantiate a
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<code class="classname">SimpleDA</code> (see <a class="xref" href="simpleda.html" title="SimpleDA.class">SimpleDA.class</a>) class that we use to access
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our primary and secondary indexes. Then we retrieve objects
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based on a primary or secondary index value. And finally, we
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display the retrieved objects.
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</p>
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<pre class="programlisting"> // Retrieve some SimpleEntityClass objects from the store.
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private void run()
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throws DatabaseException {
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setup();
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// Open the data accessor. This is used to store
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// persistent objects.
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sda = new SimpleDA(store);
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// Instantiate and store some entity classes
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SimpleEntityClass sec1 = sda.pIdx.get("keyone");
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SimpleEntityClass sec2 = sda.pIdx.get("keytwo");
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SimpleEntityClass sec4 = sda.sIdx.get("skeythree");
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System.out.println("sec1: " + sec1.getPKey());
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System.out.println("sec2: " + sec2.getPKey());
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System.out.println("sec4: " + sec4.getPKey());
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shutdown();
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} </pre>
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<p>
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Finally, to complete our class, we need a
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<code class="methodname">main()</code> method, which simply calls our
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<code class="methodname">run()</code> method.
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</p>
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<pre class="programlisting"> // main
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public static void main(String args[]) {
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SimpleStoreGet ssg = new SimpleStoreGet();
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try {
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ssg.run();
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} catch (DatabaseException dbe) {
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System.err.println("SimpleStoreGet: " + dbe.toString());
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dbe.printStackTrace();
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} catch (Exception e) {
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System.out.println("Exception: " + e.toString());
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e.printStackTrace();
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}
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System.out.println("All done.");
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}
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} </pre>
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</div>
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<div class="navfooter">
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<hr />
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||
<table width="100%" summary="Navigation footer">
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||
<tr>
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<td width="40%" align="left"><a accesskey="p" href="simpleput.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="persist_access.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="getmultiple.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">Placing Objects in an Entity Store </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> Retrieving Multiple Objects</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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