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<h1>Reading Db4o File</h1>
<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>
<pre class="prettyprint" xml:space="preserve">OffsetNavigator.Vb
Sub SearchOffset()
Dim pos As Integer
pos = Val(Selection.Text)
If pos = 0 Then
MsgBox ("The selection is not a number")
Else
ActiveDocument.Content.Characters(pos).Select
End If
End Sub</pre>
<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 value="1">open Tools/Customize/Commands/Keyboard;</li>
<li value="2"> select
"Macros" as a Category and the newly-created macro name in the Commands list;</li>
<li value="3"> press
a new key sequence for the command and press "Assign". </li>
</ul>
<p>Now you can navigate
through the human-readable db4o file using the selected key sequence.</p>
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