<html>
<head>
<META http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Activation Depth</title>
<link rel="stylesheet" type="text/css" href="../../style.css">
</head>
<body>
<div class="CommonContent">
<div class="CommonContentArea">
<h1>Activation Depth</h1><p>In order to work effectively with db4o
you must understand the concept of
<a href="../object_lifecycle/activation.html" class="wikiLink">Activation</a>. Activation controls the amount
of referenced objects loaded into the memory. There are 2 main
pitfalls that you must be aware about:</p>
<ol>
<li>
<p>An object retrieved from the
database is null.</p>
<p>This happens if the activation level
is lower than needed. For example:</p>
<p>class Pilot has field Car:</p>
<p><code>Pilot {</code></p>
<p><code>Car car;</code></p>
<p><code>}</code></p>
<p>and is saved to a database. Then
<code>pilot</code> object us retrieved from the database with the
activation depth is set to 0. In this case <code>pilot.car</code>
will be equal to null and can be incorrectly interpreted.</p>
</li>
<li>
<p>Activation depth is set
<a href="../object_lifecycle/activation/global_activation_settings.html" class="wikiLink">globally</a>
to a high value or is set to
<a href="../object_lifecycle/activation/object-specific_activation.html" class="wikiLink">cascadeOnActivate</a>
for a heavily used object with a deep structure. This will result in
a huge performance penalty and should be avoided.</p>
<p>The automatic solution of the
Activation issues is provided by
<a href="../object_lifecycle/activation/transparent_activation_framework.html" class="wikiLink">Transparent Activation Framework</a>.
However, understanding of Activation is still important.</p>
</li>
</ol>
<ul>
<p>For more information on activation
see:</p>
<li>
<p><a href="../object_lifecycle/activation/global_activation_settings.html" class="wikiLink">Global Activation Settings</a></p>
</li>
<li>
<p><a href="../object_lifecycle/activation/object-specific_activation.html" class="wikiLink">Object-Specific Activation</a></p>
</li><li>
<p><a href="../object_lifecycle/activation/transparent_activation_framework.html" class="wikiLink">Transparent Activation Framework</a></p>
</li>
<li>
<p><a href="../tuning/performance_hints/activation_strategies.html" class="wikiLink">Activation strategies</a></p>
</li>
</ul></div>
</div>
<div id="footer">
This revision (6) was last Modified 2007-11-05T16:30:34 by Tetyana.
</div>
</body>
</html>
