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<h1>Reading Db4o File</h1><script>
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</script><p>For debugging, learning and teaching
purposes, the db4o file format can be modified to be (nearly ?) human readable.</p>
<p>To do this, simply compile the sources
with Deploy.debug set to true, run an application that creates a db4o database
file and look at the file with any editor.</p>
<p>With the Deploy.debug setting all
pointers in the database file will be readable with their physical address as a
readable number.</p>
<p>All other slots will be identifiable by a
single character at the beginning. An index that explains the character
constants can be found in com.db4o.internal.Const4.</p>
<p>To understand the format best, you may
want to look at the <a href="http://developer.db4o.com/ProjectSpaces/view.aspx/Db4o_Product_Design/Db4o_Core/File_Header">File
Header</a> structure and at the #readThis() methods of classes derived from
PersistentBase, like ClassMetadataRepository for instance.</p>
<p>This functionality proved to be very
useful when db4o was originally written. By marking freespace with XXXXes a bug
in the format could be spotted immediately by visual inspection of a database
file.</p><p>To navigate through a database file in
your favourite editor, it will work best if you write a macro for this editor
that allows you to mark and select a number in the database file and to hit a
button in the editor to jump to the corresponding offset in the database file
(number of characters from the beginning).</p><p>Such macro for Microsoft Word is presented below:</p><div class="FormattedSourceCode"><div class="fscHeader"><span class="fscFileName">OffsetNavigator.Vb</span></div><div class="fscCode"><pre ID="ResourcesReferenceTuningDebugging_Db4oReading_Db4o_FileOffsetNavigator.Vb_1538_32"><div><!--
Code highlighting produced by Actipro CodeHighlighter (freeware)
http://www.CodeHighlighter.com/
--><span style="color: #008080;">1</span><img id="ResourcesReferenceTuningDebugging_Db4oReading_Db4o_FileOffsetNavigator.Vb_1538_32_0_222_Open_Image" src="../../../Utility/ActiPro.CodeHighligher/OutliningIndicators/ExpandedBlockStart.gif" align="top" onClick="this.style.display='none'; document.getElementById('ResourcesReferenceTuningDebugging_Db4oReading_Db4o_FileOffsetNavigator.Vb_1538_32_0_222_Open_Text').style.display='none'; document.getElementById('ResourcesReferenceTuningDebugging_Db4oReading_Db4o_FileOffsetNavigator.Vb_1538_32_0_222_Closed_Image').style.display='inline'; document.getElementById('ResourcesReferenceTuningDebugging_Db4oReading_Db4o_FileOffsetNavigator.Vb_1538_32_0_222_Closed_Text').style.display='inline';"/><img id="ResourcesReferenceTuningDebugging_Db4oReading_Db4o_FileOffsetNavigator.Vb_1538_32_0_222_Closed_Image" src="../../../Utility/ActiPro.CodeHighligher/OutliningIndicators/ContractedBlock.gif" align="top" style="display: none;" onClick="this.style.display='none'; document.getElementById('ResourcesReferenceTuningDebugging_Db4oReading_Db4o_FileOffsetNavigator.Vb_1538_32_0_222_Closed_Text').style.display='none'; document.getElementById('ResourcesReferenceTuningDebugging_Db4oReading_Db4o_FileOffsetNavigator.Vb_1538_32_0_222_Open_Image').style.display='inline'; document.getElementById('ResourcesReferenceTuningDebugging_Db4oReading_Db4o_FileOffsetNavigator.Vb_1538_32_0_222_Open_Text').style.display='inline';"/><span id="ResourcesReferenceTuningDebugging_Db4oReading_Db4o_FileOffsetNavigator.Vb_1538_32_0_222_Closed_Text" style="border: solid 1px #808080; background-color: #FFFFFF; display: none;">Sub SearchOffset()</span><span id="ResourcesReferenceTuningDebugging_Db4oReading_Db4o_FileOffsetNavigator.Vb_1538_32_0_222_Open_Text"><span style="color: #0000FF;">Sub</span><span style="color: #000000;"> SearchOffset()
</span><span style="color: #008080;">2</span><span style="color: #000000;"><img src="../../../Utility/ActiPro.CodeHighligher/OutliningIndicators/InBlock.gif" align="top"/> </span><span style="color: #0000FF;">Dim</span><span style="color: #000000;"> pos </span><span style="color: #0000FF;">As</span><span style="color: #000000;"> </span><span style="color: #0000FF;">Integer</span><span style="color: #000000;">
</span><span style="color: #008080;">3</span><span style="color: #000000;"><img src="../../../Utility/ActiPro.CodeHighligher/OutliningIndicators/InBlock.gif" align="top"/> pos </span><span style="color: #000000;">=</span><span style="color: #000000;"> </span><span style="color: #0000FF;">Val</span><span style="color: #000000;">(Selection.Text)
</span><span style="color: #008080;">4</span><span style="color: #000000;"><img src="../../../Utility/ActiPro.CodeHighligher/OutliningIndicators/InBlock.gif" align="top"/> </span><span style="color: #0000FF;">If</span><span style="color: #000000;"> pos </span><span style="color: #000000;">=</span><span style="color: #000000;"> </span><span style="color: #800080;">0</span><span style="color: #000000;"> </span><span style="color: #0000FF;">Then</span><span style="color: #000000;">
</span><span style="color: #008080;">5</span><span style="color: #000000;"><img src="../../../Utility/ActiPro.CodeHighligher/OutliningIndicators/InBlock.gif" align="top"/> </span><span style="color: #0000FF;">MsgBox</span><span style="color: #000000;"> (</span><span style="color: #800000;">"</span><span style="color: #800000;">The selection is not a number</span><span style="color: #800000;">"</span><span style="color: #000000;">)
</span><span style="color: #008080;">6</span><span style="color: #000000;"><img src="../../../Utility/ActiPro.CodeHighligher/OutliningIndicators/InBlock.gif" align="top"/> </span><span style="color: #0000FF;">Else</span><span style="color: #000000;">
</span><span style="color: #008080;">7</span><span style="color: #000000;"><img src="../../../Utility/ActiPro.CodeHighligher/OutliningIndicators/InBlock.gif" align="top"/> ActiveDocument.Content.Characters(pos).Select
</span><span style="color: #008080;">8</span><span style="color: #000000;"><img src="../../../Utility/ActiPro.CodeHighligher/OutliningIndicators/InBlock.gif" align="top"/> </span><span style="color: #0000FF;">End</span><span style="color: #000000;"> </span><span style="color: #0000FF;">If</span><span style="color: #000000;">
</span><span style="color: #008080;">9</span><span style="color: #000000;"><img src="../../../Utility/ActiPro.CodeHighligher/OutliningIndicators/ExpandedBlockEnd.gif" align="top"/></span><span style="color: #0000FF;">End Sub</span></span></div></pre></div></div><p>To make use of it, open Visual Basic Macro editor within your Word environment, create a new Macro in the Normal template and paste the code above. In order to make its usage easy assign a key sequence to call the macro command:</p><ul><li>open Tools/Customize/Commands/Keyboard;</li><li> select
"Macros" as a Category and the newly-created macro name in the Commands list;</li><li> press
a new key sequence for the command and press "Assign". <br></li></ul><p>Now you can navigate
through the human-readable db4o file using the selected key sequence.</p>
<p><br></p>
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This revision (1) was last Modified 2007-09-15T13:59:47 by Tetyana.
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