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<h1><a name="kanchor119"></a>Transient Fields In .NET</h1>There are different ways to prevent fields persistence in .NET:
<ul><li value="1">You can use the [com.db4o.Transient] or [NonSerialized] attribute to indicate that a field is not part of the persistent state of an object.</li><li value="2">You can use any built-in .NET attribute or
define your own attribute class and mark it transient for db4o.</li></ul><p>For example, let's create a FieldTransient attribute and mark it to prevent object persistence:</p><p MadCap:conditions="Primary..NET,Primary.c#,Primary.All languages"><pre class="prettyprint" xml:space="preserve">FieldTransient.cs
/**//* Copyright (C) 2004 - 2007 Versant Inc. http://www.db4o.com */
using System;
namespace Db4objects.Db4odoc.SelectivePersistence
{
[AttributeUsage(AttributeTargets.Field)]
public class FieldTransient: Attribute
{
}
}</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">FieldTransient.vb
' Copyright (C) 2004 - 2007 Versant Inc. http://www.db4o.com
Namespace Db4objects.Db4odoc.SelectivePersistence
<AttributeUsage(AttributeTargets.Field)> _
Public Class FieldTransient
Inherits Attribute
End Class
End Namespace</pre></p><p MadCap:conditions="Global.Primary:vb" />Let's use the newly-defined FieldTransient attribute and the system-provided Transient, and compare the results:
<p MadCap:conditions="Primary..NET,Primary.c#,Primary.All languages"><pre class="prettyprint" xml:space="preserve">Test.cs
/**//* Copyright (C) 2004 - 2007 Versant Inc. http://www.db4o.com */
using System;
namespace Db4objects.Db4odoc.SelectivePersistence
{
public class Test
{
[Db4objects.Db4o.Transient]
// you can also use [NonSerializedAttribute]
string _transientField;
string _persistentField;
public Test(string transientField, string persistentField)
{
_transientField = transientField;
_persistentField = persistentField;
}
public override string ToString()
{
return "Test: persistent: " + _persistentField + ",
transient: " + _transientField ;
}
}
}</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">Test.vb
' Copyright (C) 2004 - 2007 Versant Inc. http://www.db4o.com
Imports System
Imports Db4objects.Db4o
Namespace Db4objects.Db4odoc.SelectivePersistence
Public Class Test
<Transient()> Dim _transientField As String
' You can also use <NonSerialized()> Dim _transientField As String
' and mark the class <Serializable()>
Dim _persistentField As String
Public Sub New(ByVal transientField As String, _
ByVal persistentField As String)
_transientField = transientField
_persistentField = persistentField
End Sub
Public Overrides Function ToString() As String
Return "Test: persistent: " + _persistentField + _
", transient: " + _transientField
End Function
End Class
End Namespace</pre></p><p MadCap:conditions="Global.Primary:vb" /><p MadCap:conditions="Primary..NET,Primary.c#,Primary.All languages"><pre class="prettyprint" xml:space="preserve">TestCustomized.cs
/**//* Copyright (C) 2004 - 2007 Versant Inc. http://www.db4o.com */
namespace Db4objects.Db4odoc.SelectivePersistence
{
public class TestCustomized
{
[Db4objects.Db4odoc.SelectivePersistence.FieldTransient]
string _transientField;
string _persistentField;
public TestCustomized(string transientField, string persistentField)
{
_transientField = transientField;
_persistentField = persistentField;
}
public override string ToString()
{
return "Customized test: persistent: " + _persistentField +
", transient: " + _transientField ;
}
}
}</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">TestCustomized.vb
' Copyright (C) 2004 - 2007 Versant Inc. http://www.db4o.com
Namespace Db4objects.Db4odoc.SelectivePersistence
Public Class TestCusomized
<Db4objects.Db4odoc.SelectivePersistence.FieldTransient()> _
Dim _transientField As String
Dim _persistentField As String
Public Sub New(ByVal transientField As String, _
ByVal persistentField As String)
_transientField = transientField
_persistentField = persistentField
End Sub
Public Overrides Function ToString() As String
Return "Customized test: persistent: " + _persistentField + ", _
transient: " + _transientField
End Function
End Class
End Namespace</pre></p><p MadCap:conditions="Global.Primary:vb" /><p>We will save and retrieve both Test and TestCustomized objects, having transient fields defined in different manner: </p><p MadCap:conditions="Primary..NET,Primary.c#,Primary.All languages"><pre class="prettyprint" xml:space="preserve">MarkTransientExample.cs: SaveObjects
private static void SaveObjects(IConfiguration configuration)
{
File.Delete(Db4oFileName);
IObjectContainer container = Db4oFactory.OpenFile(configuration, Db4oFileName);
try
{
Test test = new Test("Transient string","Persistent string");
container.Store(test);
TestCustomized testc = new TestCustomized("Transient string","Persistent string");
container.Store(testc);
}
finally
{
container.Close();
}
}</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">MarkTransientExample.vb: SaveObjects
Public Shared Sub SaveObjects(ByVal configuration As IConfiguration)
File.Delete(Db4oFileName)
Dim container As IObjectContainer = _
Db4oFactory.OpenFile(configuration, Db4oFileName)
Try
Dim test As Test = New Test("Transient string", _
"Persistent string")
container.Store(test)
Dim testc As TestCusomized = New _
TestCusomized("Transient string", "Persistent string")
container.Store(testc)
Finally
container.Close()
End Try
End Sub</pre></p><p MadCap:conditions="Global.Primary:vb" />You will see the identical results independently of the way the transiency is defined.
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