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<h1>Update Depth Pitfall</h1>
<p>db4o update behavior is regulated by
<a href="../basics/update_concept.htm">Update Depth</a>. Understanding update depth
will help you to improve performance and avoid unnecessary memory
usage. A common pitfall is that the update-depth is to small and that the objects are not updated. In such cases you either need to explicitly store the
related objects individually or <a href="../configuration/common/update_depth.htm">increase the update-depth</a>.</p>
<p>For example in this code we add a new friend and store the object. Since a collection is also handled like a regular object, it is affected by the update-depth. In this example we only store the person-object, but not the friend-collection-object. Therefore with the default-update depth of one the update isn't store. In order to update this properly, you either need to set the update depth to two or store the friend-list explicitly. </p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">using (IObjectContainer container = Db4oEmbedded.OpenFile(DatabaseFile))
{
Person jodie = QueryForJodie(container);
jodie.Add(new Person("Jamie"));
// Remember that a collection is also a regular object
// so with the default-update depth of one, only the changes
// on the person-object are stored, but not the changes on
// the friend-list.
container.Store(jodie);
}
using (IObjectContainer container = Db4oEmbedded.OpenFile(DatabaseFile))
{
Person jodie = QueryForJodie(container);
foreach (Person person in jodie.Friends)
{
// the added friend is gone, because the update-depth is to low
Console.WriteLine("Friend=" + person.Name);
}
}</pre>
<div class="codesnippet-meta">UpdateDepthPitfall.cs: Update doesn't work on collection
<div class="codedownload"><a href="../CodeExamples/pitfalls/updatedepth/Example-pitfalls-updatedepth-csharp.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
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<div class="codesnippet" MadCap:conditions="Primary.VB.NET">
<pre class="prettyprint lang-vb" MadCap:conditions="Primary.Online" xml:space="preserve">Using container As IObjectContainer = Db4oEmbedded.OpenFile(DatabaseFile)
Dim jodie As Person = QueryForJodie(container)
jodie.Add(New Person("Jamie"))
' Remember that a collection is also a regular object
' so with the default-update depth of one, only the changes
' on the person-object are stored, but not the changes on
' the friend-list.
container.Store(jodie)
End Using
Using container As IObjectContainer = Db4oEmbedded.OpenFile(DatabaseFile)
Dim jodie As Person = QueryForJodie(container)
For Each person As Person In jodie.Friends
' the added friend is gone, because the update-depth is to low
Console.WriteLine("Friend=" & person.Name)
Next
End Using</pre>
<div class="codesnippet-meta">UpdateDepthPitfall.vb: Update doesn't work on collection
<div class="codedownload"><a href="../CodeExamples/pitfalls/updatedepth/Example-pitfalls-updatedepth-vb.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
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<p>So for this example setting the update-depth to two will fix the issue. For lots of operation a update-depth of two is pretty reasonable. This allows you to update collections without storing them explicitly.</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">IEmbeddedConfiguration config = Db4oEmbedded.NewConfiguration();
config.Common.UpdateDepth = 2;
using (IObjectContainer container = Db4oEmbedded.OpenFile(DatabaseFile))
{</pre>
<div class="codesnippet-meta">UpdateDepthPitfall.cs: A higher update depth fixes the issue
<div class="codedownload"><a href="../CodeExamples/pitfalls/updatedepth/Example-pitfalls-updatedepth-csharp.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
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<div class="codesnippet" MadCap:conditions="Primary.VB.NET">
<pre class="prettyprint lang-vb" MadCap:conditions="Primary.Online" xml:space="preserve">Dim config As IEmbeddedConfiguration = Db4oEmbedded.NewConfiguration()
config.Common.UpdateDepth = 2
Using container As IObjectContainer = Db4oEmbedded.OpenFile(DatabaseFile)</pre>
<div class="codesnippet-meta">UpdateDepthPitfall.vb: A higher update depth fixes the issue
<div class="codedownload"><a href="../CodeExamples/pitfalls/updatedepth/Example-pitfalls-updatedepth-vb.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
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<p>When the update depth is set to a big value
on objects with a deep reference hierarchy it will cause each update
on the top-level object to trigger updates on the lower-level
objects, which can impose a huge performance penalty.
</p>
<p>Try <a href="../basics/update_concept/transparent_persistence.htm">transparent persistence</a>, which removes the issue of the update-depth completly. </p>
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