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<h1>ASP.NET Request Example</h1>
<p>This example demonstrates how you can provide an object container for each request, to ensure that the requests are isolated from each other. For this we use session object containers. <a href="web_isolation.htm" target="" title="" alt="" class="MCXref" xrefformat="See "{paratext}"">See "Isolation in Web-Applications"</a></p>
<p>First, create a new class which implements the IHttpModule-interface. Then register this interface in the Web.config configuration:</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve"><httpModules>
<add name="Db4oDatabase" type="Db4oDoc.WebApp.Infrastructure.Db4oProvider" />
<!-- Other, existing modules-->
<add name="ScriptModule" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
<add name="UrlRoutingModule" type="System.Web.Routing.UrlRoutingModule, System.Web.Routing, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
</httpModules></pre>
<div class="codesnippet-meta">Web.config: Add the db4o-http-handler
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<p>Additionally add a key where you specify the path to the database-file. Make sure that you have the data folder inside you web-site directory. The <span class="MCPopup"><a href="javascript:void(0);" class="MCPopupSpot" onclick="FMCPopup( event, this ); return false;" MadCap:src="../asp.net.htm">ASP.NET<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> user should have enough rights to create and modify files inside this folder. You should also make sure that the data folder is not accessible to anonymous user; otherwise web-server visitors will be able to download your database:</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve"><appSettings>
<add key="DatabaseFileName" value="~/App_Data/database.db4o"/>
</appSettings></pre>
<div class="codesnippet-meta">Web.config: Database path in the configuration
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<p>After that, implement the initializing sequence. When the server starts, it starts up db4o and adds the database to the application-context:</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">public void Init(HttpApplication context)
{
if (null == HttpContext.Current.Application[DataBaseInstance])
{
HttpContext.Current.Application[DataBaseInstance] = OpenDatabase();
}
RegisterSessionCreation(context);
}
private IEmbeddedObjectContainer OpenDatabase()
{
string relativePath = ConfigurationSettings.AppSettings["DatabaseFileName"];
string filePath = HttpContext.Current.Server.MapPath(relativePath);
return Db4oEmbedded.OpenFile(filePath);
}</pre>
<div class="codesnippet-meta">Db4oProvider.cs: open database when the application starts
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<p>On the dispose-method add the shutdown code:</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">public void Dispose()
{
IDisposable toDispose = HttpContext.Current.Application[DataBaseInstance] as IDisposable;
if (null != toDispose)
{
toDispose.Dispose();
}
}</pre>
<div class="codesnippet-meta">Db4oProvider.cs: close the database when the application shuts down
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<p>Now it's time to ensure that each requests has its own object container. To archive that, use the <a href="web_isolation.htm">open-session-method</a>. Register for the request-begin and request-end events. In begin session event, open a new db4o session. In the end request event, close that session.</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">private void RegisterSessionCreation(HttpApplication httpApplication)
{
httpApplication.BeginRequest += OpenSession;
httpApplication.EndRequest += CloseSession;
}
private void OpenSession(object sender, EventArgs e)
{
IObjectContainer container =
(IObjectContainer)HttpContext.Current.Application[DataBaseInstance];
IObjectContainer session = container.Ext().OpenSession();
HttpContext.Current.Items[SessionKey] = session;
}
private void CloseSession(object sender, EventArgs e)
{
IObjectContainer session = (IObjectContainer)HttpContext.Current.Items[SessionKey];
session.Dispose();
}</pre>
<div class="codesnippet-meta">Db4oProvider.cs: A object container per request
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<p>Finally add a static property which gives access to the request-instance:</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">public static IObjectContainer Database
{
get { return (IObjectContainer)HttpContext.Current.Items[SessionKey]; }
}</pre>
<div class="codesnippet-meta">Db4oProvider.cs: provide access to the database
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<p>That's it. Of course there are other ways to archive the same result. For example you can use dependency injection frameworks like <a href="http://unity.codeplex.com/">Microsoft's Unity</a> to enforce the request scope.</p>
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