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<head><title>Accessing Persistent Classes From Different .NET Applications </title>
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<h1>Accessing Persistent Classes From Different .NET Applications</h1>
<h2>Problem</h2>
<p>Accessing db4o database created and filled in with a .NET
application or library from another .NET application or library shows an empty
database.</p>
<h2>Reason</h2>
<p>db4o class name format in db4o consists of the full class
name and assembly name:</p>
<p><code>Namespace.ClassName, AssemblyName</code>
</p>
<p>Two different .NET applications (libraries) usually have
different assembly names. If you do not use
<a href="../configuration/common/alias.htm">aliasing</a>, the class name will be appended
with the current application assembly name.</p>
<h2>Solution</h2>
<p>In order to access db4o persistent classes from different
applications (libraries) you will need to use an
<a href="../configuration/common/alias.htm">Alias</a>. For example:</p>
<p><b>Application1.exe ("Application1" assembly):</b>
</p>
<p><code>objectContainer.Store(new MyClasses.Pilot("David
Barrichello",99))</code>
</p>
<p><code>// internally the class is saved as "MyClasses.Pilot,
Application1".</code>
</p>
<p><b>Application2.exe ("Application2" assembly):</b>
</p>
<p MadCap:conditions="Primary..NET,Primary.c#,Primary.All languages">
<p>c#:</p>
<p><code>// create an <span class="MCPopup"><a href="javascript:void(0);" class="MCPopupSpot" onclick="FMCPopup( event, this ); return false;" MadCap:src="../configuration/common/alias.htm">Alias<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> for the MyClasses.Pilot,
Application1:</code>
</p>
<p><code>IEmbeddedConfiguration configuration =
Db4oEmbedded.NewConfiguration();</code>
</p>
<p><code>configuration.Common.AddAlias(new
TypeAlias("MyClasses.Pilot, Application1", " MyClasses.Pilot, Application2"));</code>
</p>
<p><code>IObjectContainer container =
Db4oEmbedded.OpenFile(configuration, "reference.db4o");</code>
</p>
<p><code>// now you query as usual</code>
</p>
<p><code>IObjectSet result = container.QueryByExample(new
Test());</code>
</p>
</p>
<p MadCap:conditions="Global.Primary:cs" />
<p MadCap:conditions="Primary..NET,Primary.VB.NET,Primary.All languages">
<p>VB:</p>
<p><code>// create an Alias for the MyClasses.Pilot,
Application1:</code>
</p>
<p><code>Dim configuration As IEmbeddedConfiguration = Db4oEmbedded.NewConfiguration()</code>
</p>
<p><code>configuration.Common.AddAlias(new
TypeAlias("MyClasses.Pilot, Application1", " MyClasses.Pilot, Application2"))</code>
</p>
<p><code>Dim container As IObjectContainer =
Db4oEmbedded.OpenFile(configuration, "reference.db4o")</code>
</p>
<p><code>// now you query as usual</code>
</p>
<p><code>Dim result As IObjectSet = container.QueryByExample(New
Test())</code>
</p>
</p>
<p MadCap:conditions="Global.Primary:vb" />
<p>For more information see
<a href="../platform_specific_issues/class_name_format_in_.net.htm">Class Name Format In .NET</a> and
<a href="../configuration/common/alias.htm">Aliases</a>.</p>
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