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115 lines
4.9 KiB
HTML
115 lines
4.9 KiB
HTML
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<?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>Deleting Entity Objects</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="dpl_entityjoin.html" title="Join Cursors" />
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<link rel="next" href="dpl_replace.html" title="Replacing Entity 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">Deleting Entity Objects</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="dpl_entityjoin.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="dpl_replace.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="dpl_delete"></a>Deleting Entity Objects</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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The simplest way to remove an object from your entity store
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is to delete it by its primary index. For example,
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using the <code class="classname">SimpleDA</code> class that we
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created earlier in this document
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(see <a class="xref" href="simpleda.html" title="SimpleDA.class">SimpleDA.class</a>),
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you can delete the <code class="classname">SimpleEntityClass</code>
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object with a primary key of <code class="literal">keyone</code> as
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follows:
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</p>
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<pre class="programlisting">sda.pIdx.delete("keyone");</pre>
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<p>
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You can also delete objects by their secondary keys. When
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you do this, all objects related to the secondary key are
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deleted, unless the key is a foreign object.
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</p>
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<p>
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For example, the following deletes all
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<code class="classname">SimpleEntityClass</code> with a secondary
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key of <code class="literal">skeyone</code>:
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</p>
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<pre class="programlisting">sda.sIdx.delete("skeyone");</pre>
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<p>
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You can delete any single object by positioning a cursor to
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that object and then calling the cursor's
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<code class="methodname">delete()</code> method.
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</p>
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<pre class="programlisting">PrimaryIndex<String,SimpleEntityClass> pi =
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store.getPrimaryIndex(String.class, SimpleEntityClass.class);
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SecondaryIndex<String,String,SimpleEntityClass> si =
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store.getSecondaryIndex(pi, String.class, "sKey");
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EntityCursor<SimpleEntityClass> sec_cursor =
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si.subIndex("skeyone").entities();
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try {
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SimpleEntityClass sec;
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Iterator<SimpleEntityClass> i = sec_cursor.iterator();
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while (sec = i.nextDup() != null) {
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if (sec.getSKey() == "some value") {
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i.delete();
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}
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}
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// Always make sure the cursor is closed when we are done with it.
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} finally {
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sec_cursor.close(); } </pre>
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<p>
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Finally, if you are indexing by foreign key, then the
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results of deleting the key is determined by the foreign
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key constraint that you have set for the index. See
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<a class="xref" href="dplindexcreate.html#foreignkey" title="Foreign Key Constraints">Foreign Key Constraints</a>
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for more information.
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</p>
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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="dpl_entityjoin.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="dpl_replace.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">Join Cursors </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"> Replacing Entity 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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