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<h1><a name="kanchor29"></a>Update Concept</h1>
<p>Updating objects in db4o is as easy as storing them. You just call then store-method again to update a object. How does a update work? There are two main questions. First, how does db4o recognize a object so that it knows whenever it should update a object or store it as a new object? And what's the scope of updates? All all objects updated? Or just the objects you explicitly store?</p>
<h2>Object Recognition</h2>
<p>How does db4o know which object needs to be updated and which object has to be stored as new object? Well db4o uses the <a href="identity_concept.htm">object-identity</a> and looks up it if has loaded this object. If the object was loaded by db4o, it is an existing object and will be updated. Otherwise it has to be a new object and is stored as a new object.</p>
<h2>Update Depth</h2>
<p>When you update of a object, db4o only stores the changes to a certain depth. This update depth avoids that db4o needs to go through the whole object graph and find out which objects have changed. </p>
<p>By default this update depth is one. This means when you update a object, only the changes on that object are stored. Changes on other objects are not included. When you want to store changes of multiple objects you need either to increase the <a href="../configuration/common/update_depth.htm">update-depth</a>, store each object individually or use <a href="update_concept/transparent_persistence.htm">transparent persistence</a>. </p>
<p>Take a look at this concrete example to see how the update-depth affects you're operations. <a href="update_concept/update_depth_in_action.htm" target="" title="" alt="" class="MCXref" xrefformat="See "{paratext}"">See "Update Depth In Action"</a></p>
<p>Since collection are regular object in db4o the update depth also applies to collections. <a href="update_concept/updating_collections.htm" target="" title="" alt="" class="MCXref" xrefformat="See "{paratext}"">See "Updating Collections"</a></p>
<p>If you want to automate the update process of object: <a href="update_concept/transparent_persistence.htm" target="" title="" alt="" class="MCXref" xrefformat="See "{paratext}"">See "Transparent Persistence"</a></p>
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