<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns:MadCap="http://www.madcapsoftware.com/Schemas/MadCap.xsd" MadCap:lastBlockDepth="2" MadCap:lastHeight="120" MadCap:lastWidth="624" MadCap:disableMasterStylesheet="true" MadCap:tocPath="Advanced Features|Type Handling|Blobs" MadCap:InPreviewMode="false" MadCap:RuntimeFileType="Topic" MadCap:TargetType="WebHelp" MadCap:PathToHelpSystem="../../../../" MadCap:HelpSystemFileName="index.xml" MadCap:SearchType="Stem">
<head><title>Db4o Blob Implementation</title>
<script type="text/javascript">/* <![CDATA[ */
window.onload = function(){
var pathToFlash = $('html').attr('MadCap:PathToHelpSystem') + 'Content/Resources/Code/ZeroClipboard.swf';
ZeroClipboard.setMoviePath(pathToFlash);
function bindToClipBord(element,content){
var clip = new ZeroClipboard.Client();
clip.setText(content);
clip.glue(element);
};
if(location.protocol==='file:'){
$('.copylink-marker').remove();
} else{
$('.copylink-marker').each(function(){
var text = $(this).parent().parent().children('.prettyprint').html();
$(this).hover(function(){
bindToClipBord(this,text);
},
function(){});
});
}
prettyPrint();
};
/* ]]> */</script>
<link href="../../../SkinSupport/MadCap.css" rel="stylesheet" />
<link href="../../../Resources/Stylesheets/OnlineStyle.css" rel="stylesheet" />
<script src="../../../Resources/Code/prettify.js">
</script>
<script src="../../../Resources/Code/lang-vb.js">
</script>
<script src="../../../Resources/Code/jquery.min.js">
</script>
<script src="../../../Resources/Code/ZeroClipboard.js">
</script>
<script src="../../../SkinSupport/MadCapAll.js" type="text/javascript">
</script>
</head>
<body>
<p class="MCWebHelpFramesetLink" style="display: none;"><a href="../../../../index_CSH.html#advanced_topics/type_handling/blobs/db4o_blob_implementation.htm" style="">Open topic with navigation</a>
</p>
<div class="MCBreadcrumbsBox"><span class="MCBreadcrumbsPrefix">You are here: </span><a class="MCBreadcrumbsLink" href="../../../advanced_topics.htm">Advanced Features</a><span class="MCBreadcrumbsDivider"> > </span><a class="MCBreadcrumbsLink" href="../../type_handling.htm">Type Handling</a><span class="MCBreadcrumbsDivider"> > </span><a class="MCBreadcrumbsLink" href="../blobs.htm">Blobs</a><span class="MCBreadcrumbsDivider"> > </span><span class="MCBreadcrumbs">Db4o Blob Implementation</span>
</div>
<p>
<script type="text/javascript">/*<![CDATA[*/document.write('<a href="' + location.href +'">');
document.write("Direct Link");
document.write('</a>');/*]]>*/</script>
</p>
<p>
</p>
<h1>Db4o Blob Implementation</h1>
<p>Built-in db4o blob type helps you to get rid of the problems of byte[] array, though it has its own drawbacks. </p>
<ol>
<li value="1">Every Blob gets it's own file:</li>
<p>+ Main database file stays a lot smaller. </p>
<p>+ Backups are possible over individual files.</p>
<p>+The BLOBs are accessible without db4o.</p>
<p>- Multiple files need to be managed .</p>
</ol>
<ol>
<li value="1">Special code is necessary to store and load.</li>
<p>- It is more difficult to move objects between db4o database files.</p>
<li value="2">No concerns about activation depth</li>
<p>+ Big objects won't be loaded into memory as part of the activation process.</p>
</ol>
<h2>Configuration</h2>
<p>First, the <a href="../../../configuration/file/blob_path.htm">blob storage location</a> should be defined. If that value is not defined, db4o will use the default folder "blobs" in user directory.</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">IEmbeddedConfiguration configuration = Db4oEmbedded.NewConfiguration();
configuration.File.BlobPath = "myBlobDirectory";</pre>
<div class="codesnippet-meta">FileConfiguration.cs: Configure the blob-path
<div class="codedownload"><a href="../../../CodeExamples/configuration/file/Example-configuration-file-csharp.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
</div>
<div class="codesnippet" MadCap:conditions="Primary.VB.NET">
<pre class="prettyprint lang-vb" MadCap:conditions="Primary.Online" xml:space="preserve">Dim configuration As IEmbeddedConfiguration = Db4oEmbedded.NewConfiguration()
configuration.File.BlobPath = "myBlobDirectory"</pre>
<div class="codesnippet-meta">FileConfiguration.vb: Configure the blob-path
<div class="codedownload"><a href="../../../CodeExamples/configuration/file/Example-configuration-file-vb.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
</div>
<h2>Using The db4o-Blob</h2>
<p>There are two important operations on the blob type. The first one write a file into the db4o blob:</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">blob.ReadFrom(fileToStore);</pre>
<div class="codesnippet-meta">BlobStorage.cs: Store the file as a db4o-blob
<div class="codedownload"><a href="../../../CodeExamples/typehandling/blob/Example-typehandling-blob-csharp.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
</div>
<div class="codesnippet" MadCap:conditions="Primary.VB.NET">
<pre class="prettyprint lang-vb" MadCap:conditions="Primary.Online" xml:space="preserve">blob.ReadFrom(fileToStore)</pre>
<div class="codesnippet-meta">BlobStorage.vb: Store the file as a db4o-blob
<div class="codedownload"><a href="../../../CodeExamples/typehandling/blob/Example-typehandling-blob-vb.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
</div>
<p>And then there's the operation which .loads the db4o blob into a new file. </p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">blob.WriteTo(file);</pre>
<div class="codesnippet-meta">BlobStorage.cs: Load a blob from a db4o-blob
<div class="codedownload"><a href="../../../CodeExamples/typehandling/blob/Example-typehandling-blob-csharp.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
</div>
<div class="codesnippet" MadCap:conditions="Primary.VB.NET">
<pre class="prettyprint lang-vb" MadCap:conditions="Primary.Online" xml:space="preserve">blob.WriteTo(file)</pre>
<div class="codesnippet-meta">BlobStorage.vb: Load a blob from a db4o-blob
<div class="codedownload"><a href="../../../CodeExamples/typehandling/blob/Example-typehandling-blob-vb.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
</div>
<p>The db4o blob-type has a status attached to it. This status tells you if the blob-file all ready has been transferred:</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">while (blob.GetStatus() > Status.Completed)
{
Thread.Sleep(50);
}</pre>
<div class="codesnippet-meta">BlobStorage.cs: wait until the operation is done
<div class="codedownload"><a href="../../../CodeExamples/typehandling/blob/Example-typehandling-blob-csharp.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
</div>
<div class="codesnippet" MadCap:conditions="Primary.VB.NET">
<pre class="prettyprint lang-vb" MadCap:conditions="Primary.Online" xml:space="preserve">While blob.GetStatus() > Status.Completed
Thread.Sleep(50)
End While</pre>
<div class="codesnippet-meta">BlobStorage.vb: wait until the operation is done
<div class="codedownload"><a href="../../../CodeExamples/typehandling/blob/Example-typehandling-blob-vb.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
</div>
<p MadCap:conditions="Primary..NET,Primary.Online">Take a look a the complete example code (<span MadCap:conditions="Primary..NET"><a href="../../../CodeExamples/typehandling/blob/Example-typehandling-blob-csharp.zip">C#</a>, <a href="../../../CodeExamples/typehandling/blob/Example-typehandling-blob-vb.zip">VB.NET</a></span>).</p>
<script type="text/javascript" src="../../../SkinSupport/MadCapBodyEnd.js">
</script>
</body>
</html>
