mirror of
https://github.com/berkeleydb/je.git
synced 2024-10-05 05:36:55 +00:00
124 lines
5.5 KiB
HTML
124 lines
5.5 KiB
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>Saving and Retrieving Data</title>
|
|||
|
|
<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
|
|||
|
|
<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
|
|||
|
|
<link rel="start" href="index.html" title="Getting Started with Berkeley DB Java Edition" />
|
|||
|
|
<link rel="up" href="persist_first.html" title="Chapter 3. Direct Persistence Layer First Steps" />
|
|||
|
|
<link rel="prev" href="persistobject.html" title="Persistent Objects" />
|
|||
|
|
<link rel="next" href="persist_index.html" title="Chapter 4. Working with Indices" />
|
|||
|
|
</head>
|
|||
|
|
<body>
|
|||
|
|
<div xmlns="" class="navheader">
|
|||
|
|
<div class="libver">
|
|||
|
|
<p>Library Version 12.2.7.5</p>
|
|||
|
|
</div>
|
|||
|
|
<table width="100%" summary="Navigation header">
|
|||
|
|
<tr>
|
|||
|
|
<th colspan="3" align="center">Saving and Retrieving Data</th>
|
|||
|
|
</tr>
|
|||
|
|
<tr>
|
|||
|
|
<td width="20%" align="left"><a accesskey="p" href="persistobject.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="persist_index.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="saveret"></a>Saving and Retrieving Data</h2>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
<p>
|
|||
|
|
All data stored using the DPL has one primary index and
|
|||
|
|
zero or more secondary indices associated with it.
|
|||
|
|
(Sometimes these are referred to as the primary and
|
|||
|
|
secondary <span class="emphasis"><em>keys</em></span>.) So to store data under the DPL, you must:
|
|||
|
|
</p>
|
|||
|
|
<div class="orderedlist">
|
|||
|
|
<ol type="1">
|
|||
|
|
<li>
|
|||
|
|
<p>
|
|||
|
|
Declare a class to be an entity class.
|
|||
|
|
</p>
|
|||
|
|
</li>
|
|||
|
|
<li>
|
|||
|
|
<p>
|
|||
|
|
Identify the features on the class which
|
|||
|
|
represent indexed material.
|
|||
|
|
</p>
|
|||
|
|
</li>
|
|||
|
|
<li>
|
|||
|
|
<p>
|
|||
|
|
Retrieve the store's primary index for a
|
|||
|
|
given class using the
|
|||
|
|
<code class="methodname">EntityStore.getPrimaryIndex()</code>
|
|||
|
|
method.
|
|||
|
|
</p>
|
|||
|
|
</li>
|
|||
|
|
<li>
|
|||
|
|
<p>
|
|||
|
|
Put class objects to the store using the
|
|||
|
|
<code class="methodname">PrimaryIndex.put()</code>
|
|||
|
|
method.
|
|||
|
|
</p>
|
|||
|
|
</li>
|
|||
|
|
</ol>
|
|||
|
|
</div>
|
|||
|
|
<p>
|
|||
|
|
In order to retrieve an object from the store, you use
|
|||
|
|
the index that is most convenient for your purpose. This
|
|||
|
|
may be the primary index, or it may be some other
|
|||
|
|
secondary index that you declared on your entity class.
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
You obtain a primary index in the same was as when you
|
|||
|
|
put the object to the store: using
|
|||
|
|
<code class="methodname">EntityStore.getPrimaryIndex()</code>.
|
|||
|
|
You can get a secondary index for the store using the
|
|||
|
|
<code class="methodname">EntityStore.getSecondaryIndex()</code>
|
|||
|
|
method. Note that
|
|||
|
|
<code class="methodname">getSecondaryIndex()</code> requires you
|
|||
|
|
to provide a <code class="classname">PrimaryIndex</code> class
|
|||
|
|
instance when you call it, so a class's primary index is
|
|||
|
|
always required when retrieving objects from an entity
|
|||
|
|
store.
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
Usually all of the activity surrounding saving and
|
|||
|
|
retrieving data is organized within a class or classes
|
|||
|
|
specialized to that purpose. We describe the construction
|
|||
|
|
of these data accessor classes in <a class="xref" href="simpleda.html" title="SimpleDA.class">SimpleDA.class</a>. But before you perform
|
|||
|
|
any entity store activity, you need to understand
|
|||
|
|
indexes. We therefore describe them in the next chapter.
|
|||
|
|
</p>
|
|||
|
|
</div>
|
|||
|
|
<div class="navfooter">
|
|||
|
|
<hr />
|
|||
|
|
<table width="100%" summary="Navigation footer">
|
|||
|
|
<tr>
|
|||
|
|
<td width="40%" align="left"><a accesskey="p" href="persistobject.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="persist_index.html">Next</a></td>
|
|||
|
|
</tr>
|
|||
|
|
<tr>
|
|||
|
|
<td width="40%" align="left" valign="top">Persistent Objects </td>
|
|||
|
|
<td width="20%" align="center">
|
|||
|
|
<a accesskey="h" href="index.html">Home</a>
|
|||
|
|
</td>
|
|||
|
|
<td width="40%" align="right" valign="top"> Chapter 4. Working with Indices</td>
|
|||
|
|
</tr>
|
|||
|
|
</table>
|
|||
|
|
</div>
|
|||
|
|
</body>
|
|||
|
|
</html>
|