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copied!<p>Activation: As you said db4o uses it's <a href="http://developer.db4o.com/Documentation/Reference/db4o-8.0/net35/reference/Content/basics/activation.htm" rel="nofollow">activation-mechanism</a> to control which objects are loaded. To prevent that to many objects are loaded there are different strategies.</p> <ul> <li>Lower the <a href="http://developer.db4o.com/Documentation/Reference/db4o-8.0/net35/reference/Content/configuration/common/activation_depth.htm" rel="nofollow">global default activation-depth</a>: <code>configuration.Common.ActivationDepth = 2</code> Then use the strategies below to activate objects on need.</li> <li>Use class-specific activation configuration like <a href="http://developer.db4o.com/Documentation/Reference/db4o-8.0/net35/reference/Content/configuration/objectclass/cascade_on-activate.htm" rel="nofollow">cascading activation</a>, <a href="http://developer.db4o.com/Documentation/Reference/db4o-8.0/net35/reference/Content/configuration/objectclass/minimum_activation_depth.htm" rel="nofollow">minimum</a> and <a href="http://developer.db4o.com/Documentation/Reference/db4o-8.0/net35/reference/Content/configuration/objectclass/maximum_activation_depth.htm" rel="nofollow">maximun</a> activation-depth etc.</li> <li>Activate objects explicit on demand: <code>container.Activate(theObject,5)</code></li> </ul> <p>However all these stuff is rather painful on complex object graphs. The only strategy to get away from that pain is <a href="http://developer.db4o.com/Documentation/Reference/db4o-8.0/net35/reference/Content/basics/activation_concept/transparent_activation_framework/ta_enhanced_example/ta_enhancement_with_db4otool.htm" rel="nofollow">transparent activation</a>. Create an attribute like TransparentlyActivated. Use this attribute to mark your stored classes. Then use the <a href="http://developer.db4o.com/Documentation/Reference/db4o-8.0/net35/reference/Content/advanced_topics/enhancement_tools/enhancement_for_.net/db4otool.htm" rel="nofollow">db4otool</a> to enhance your classes. Add the db4otool-command to the Post-Build events in Visual Studio: Like <code>'PathTo\Db4oTool.exe -ta -debug -by-attribute:YourNamespace.TransparentlyActivated $(TargetPath)</code></p> <p>Guid, Generic Collections: No (in Version 7.12 or 8.0). However if you store your own structs: Those are handled very poorly by db4o</p> <p>WebApplication: I recommend an embedded-container, and then a <a href="http://developer.db4o.com/Documentation/Reference/db4o-8.0/net35/reference/Content/platform_specific_issues/web_environment.htm" rel="nofollow">session-container for each request</a>.</p> <p><strong>Update for extended question part</strong></p> <p>To your case. For such complex activation schema I would use transparent activation. I assume you are using properties and not public fields in your real scenario, otherwise transparent persistence doesn't work.</p> <p>The transparent activation basically loads an object in the moment a method/property is called the first. So when you access the property A.R then A itself it loaded, but not the referenced objects. I just go through a few of you access patterns to show what I mean:</p> <p>Getting 'A.BList.C.BList.A.R'</p> <ul> <li>A is loaded when you access A.BList. The BList array is filled with unactivate objects</li> <li>You keep navigating further to BList.C. At this moment the BList object is loaded</li> <li>Then you access C.BList. db4o loads the C-object</li> <li>And so on and so forth.</li> </ul> <p>So when you get 'A.BList.C.BList.A.R' then 'A.R' isn't loaded</p> <p>A unloaded object is represented by an 'empty'-shell object, which has all values set to null or the default value. Arrays are always fully loaded, but first filled with unactivated objects.</p> <p>Note that theres no real query syntax to do some kind of elaborate load requests. You load your start object and then pull stuff in as you need it.</p> <p>I also need to mention that this kind of access will perform terrible over the network with db4o. </p> <p>Yet another hint. If you want to do elaborate work on a graph-structure, you also should take a look at graph databases, like <a href="http://neo4j.org/" rel="nofollow">Neo4J</a> or <a href="http://www.sones.com/home" rel="nofollow">Sones Graph DB</a></p>

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