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<h1>Rollback And Cache</h1>
<p>Suppose we have <a href="car.htm">Car</a>, <a href="pilot.htm">Pilot</a> and <a href="id.htm">Id</a> classes stored in the database. Car class is activatable, others are not. We
will modify the car and rollback the transaction:</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: ModifyAndRollback
private static void ModifyAndRollback()
{
IObjectContainer container = Database(ConfigureTP());
if (container != null)
{
try
{
// create a car
Car car = (Car)container.QueryByExample(new Car(null, null))
[0];
System.Console.WriteLine("Initial car: " + car + "("
+ container.Ext().GetID(car) + ")");
car.Model = "Ferrari";
car.Pilot = new Pilot("Michael Schumacher", 123);
container.Rollback();
System.Console.WriteLine("Car after rollback: " + car + "("
+ container.Ext().GetID(car) + ")");
}
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: ModifyAndRollback
Private Shared Sub ModifyAndRollback()
Dim container As IObjectContainer = Database(ConfigureTP())
If container IsNot Nothing Then
Try
' create a car
Dim car As Car = DirectCast(container. _ 
QueryByExample(New Car(Nothing, Nothing))(0), Car)
System.Console.WriteLine("Initial car: " + _
car.ToString() + "(" + container.Ext().GetID(car).ToString() + ")")
car.Model = "Ferrari"
car.Pilot = New Pilot("Michael Schumacher", 123)
container.Rollback()
System.Console.WriteLine("Car after rollback: " _
+ car.ToString() + "(" + _
container.Ext().GetID(car).ToString() + ")")
Finally
CloseDatabase()
End Try
End If
End Sub</pre>
</p>
<p MadCap:conditions="Global.Primary:vb" />
<p>If the transaction was going on normally (commit), we would
have had the car modified in the database as it is supported by Transparent
Persistence. However, as the transaction was rolled back - no modifications
should be done to the database. The result that is printed to the screen is
taken from the reference cache, so it will show modified objects. That is
confusing and should be fixed:</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: ModifyRollbackAndCheck
private static void ModifyRollbackAndCheck()
{
IObjectContainer container = Database(ConfigureTP());
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();
container.Deactivate(car, Int32.MaxValue);
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: ModifyRollbackAndCheck
Private Shared Sub ModifyRollbackAndCheck()
Dim container As IObjectContainer = Database(ConfigureTP())
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()
container.Deactivate(car, Int32.MaxValue)
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>Here we've added a <code>deactivate</code> call for the car
object. This call is used to clear the reference cache and its action is
reversed to <code>activate</code>. </p>
<p>We've used max int to deactivate
car fields to the maximum possible depth. Thus we can be sure that all the car
fields will be re-read from the database again (no outdated values from the
reference cache), but the trade-off is that all child objects will be
deactivated and read from the database too. You can see it on Pilot object.
This behaviour is preserved for both activatable and non-activatable objects.</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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