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<h1>Automatic Deactivation</h1>
<p>
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<p>The use of depth parameter in <code>deactivate</code> call from
the <a href="rollback_and_cache.htm">previous example</a> directly affects performance: the
less is the depth the less objects will need to be re-read from the database
and the better the performance will be. Ideally we only want to deactivate the
objects that were changed in the rolled-back transaction. This can be done by
providing a special class for db4o configuration. This class should implement
<code>RollbackStrategy/IRollbackStrategy</code> interface and is configured as
part of Transparent Persistence support:</p>
<p MadCap:conditions="Global.Primary:java" />
<p MadCap:conditions="Primary..NET,Primary.c#,Primary.All languages">
<pre class="prettyprint" xml:space="preserve">TPRollback.cs: RollbackDeactivateStrategy
private class RollbackDeactivateStrategy : IRollbackStrategy
{
public void Rollback(IObjectContainer container, Object obj)
{
container.Ext().Deactivate(obj);
}
}</pre>
<pre class="prettyprint" xml:space="preserve">TPRollback.cs: ConfigureTPForRollback
private static IConfiguration ConfigureTPForRollback()
{
IConfiguration configuration = Db4oFactory.NewConfiguration();
// add <span class="MCTextPopup"><a href="javascript:void(0);" class="MCTextPopupSpot" onclick="FMCTextPopup( event, this ); return false;">TP<img style="border: none;margin-left: 5px;" src="../../../../../SkinSupport/ExpandingClosed.gif" MadCap:altsrc="../../../../../SkinSupport/ExpandingOpen.gif" class="MCExpandingIcon" onload="if ( typeof( FMCPreloadImage ) == 'function' ) { FMCPreloadImage( '../../../../../SkinSupport/ExpandingOpen.gif' ); }" /></a><span class="MCTextPopupBody" style="display: none; ">Transparent Persistence</span></span> support and rollback strategy
configuration.Add(new TransparentPersistenceSupport(
new RollbackDeactivateStrategy()));
return configuration;
}</pre>
</p>
<p MadCap:conditions="Global.Primary:cs" />
<p MadCap:conditions="Primary..NET,Primary.VB.NET,Primary.All languages">
<pre class="prettyprint lang-vb" xml:space="preserve">TPRollback.vb: RollbackDeactivateStrategy
Private Class RollbackDeactivateStrategy
Implements IRollbackStrategy
Public Sub Rollback(ByVal container As IObjectContainer, _
ByVal obj As Object) _
Implements IRollbackStrategy.Rollback
container.Ext().Deactivate(obj)
End Sub
End Class</pre>
<pre class="prettyprint lang-vb" xml:space="preserve">TPRollback.vb: ConfigureTPForRollback
Private Shared Function ConfigureTPForRollback() As IConfiguration
Dim configuration As IConfiguration = Db4oFactory.NewConfiguration()
' add TP support and rollback strategy
configuration.Add(New TransparentPersistenceSupport _
(New RollbackDeactivateStrategy()))
Return configuration
End Function</pre>
</p>
<p MadCap:conditions="Global.Primary:vb" />
<p>RollbackDeactivateStrategy#rollback method will be
automatically called <b>once</b> per each <b>modified</b> object after the rollback.
Thus you do not have to worry about deactivate depth anymore - all necessary
deactivation will happen transparently preserving the best performance
possible. </p>
<p MadCap:conditions="Global.Primary:java" />
<p MadCap:conditions="Primary..NET,Primary.c#,Primary.All languages">
<pre class="prettyprint" xml:space="preserve">TPRollback.cs: ModifyWithRollbackStrategy
private static void ModifyWithRollbackStrategy()
{
IObjectContainer container = Database(ConfigureTPForRollback());
if (container != null)
{
try
{
// create a car
Car car = (Car)container.QueryByExample(new Car(null, null))
[0];
Pilot pilot = car.Pilot;
System.Console.WriteLine("Initial car: " + car + "("
+ container.Ext().GetID(car) + ")");
System.Console.WriteLine("Initial pilot: " + pilot + "("
+ container.Ext().GetID(pilot) + ")");
car.Model = "Ferrari";
car.ChangePilot("Michael Schumacher", 123);
container.Rollback();
System.Console.WriteLine("Car after rollback: " + car + "("
+ container.Ext().GetID(car) + ")");
System.Console.WriteLine("Pilot after rollback: " + pilot + "("
+ container.Ext().GetID(pilot) + ")");
}
finally
{
CloseDatabase();
}
}
}</pre>
</p>
<p MadCap:conditions="Global.Primary:cs" />
<p MadCap:conditions="Primary..NET,Primary.VB.NET,Primary.All languages">
<pre class="prettyprint lang-vb" xml:space="preserve">TPRollback.vb: ModifyWithRollbackStrategy
Private Shared Sub ModifyWithRollbackStrategy()
Dim container As IObjectContainer = Database(ConfigureTPForRollback())
If container IsNot Nothing Then
Try
' create a car
Dim car As Car = DirectCast(container. _
QueryByExample(New Car(Nothing, Nothing))(0), Car)
Dim pilot As Pilot = car.Pilot
System.Console.WriteLine("Initial car: " + _
car.ToString() + "(" + container.Ext().GetID(car).ToString() + ")")
System.Console.WriteLine("Initial pilot: " + _
pilot.ToString() + "(" + _
container.Ext().GetID(pilot).ToString() + ")")
car.Model = "Ferrari"
car.ChangePilot("Michael Schumacher", 123)
container.Rollback()
System.Console.WriteLine("Car after rollback: " + _
car.ToString() + "(" + _
container.Ext().GetID(car).ToString() + ")")
System.Console.WriteLine("Pilot after rollback: " + _
pilot.ToString() + _
"(" + container.Ext().GetID(pilot).ToString() + ")")
Finally
CloseDatabase()
End Try
End If
End Sub</pre>
</p>
<p MadCap:conditions="Global.Primary:vb" />
<p>Note, that RollbackDeactivateStrategy <b>only works for activatable</b> objects. To see the different you can
comment out Activatable implementation in Id class (id value will be preserved
in the cache).</p>
<p MadCap:conditions="Primary.Online">Download example code:</p>
<p MadCap:conditions="Primary.Online">
<MadCap:conditionalText MadCap:conditions="Primary..NET,Primary.VB.NET,Primary.All languages"><a href="../rollbackvb.zip">VB.NET </a>
</MadCap:conditionalText>
<MadCap:conditionalText MadCap:conditions="Primary..NET,Primary.c#,Primary.All languages"><a href="../rollbackcs.zip">c# </a>
</MadCap:conditionalText>
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