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<h1>Object Manager Specifics</h1><div id="TOC"><div id="TOCinner"><span class="TOCtitle">Contents</span><div class="TOCcontents"><ul><li><a href ="#Java enumerations">Java enumerations</a></li></ul></li></ul></div></div></div><p><br></p><p>Object Manager can operate on any java or .NET db4o
database, because it does not need class definitions to instantiate database
objects. Instead of real classes ObjectManager in fact instantiates
<a href="../implementation_strategies/db4o_reflection_api/genericreflector.html" class="wikiLink">Generic
Objects</a>, which hold a database object information in an array of fields. This
approach is very powerful, however it introduces some limitations.</p><a name="Java enumerations"></a><h2>Java enumerations</h2>
<p>Java enumerations (java.lang.Enum) hold the information in
<code>name</code> and <code>ordinal</code> fields. However, when an enumeration
is used in a persistent object it is not really necessary to save the whole
enumeration to the database, as it will be available from the classloader in
runtime. That is why db4o only saves the actual enumeration values together
with the object, and the values are bind to the enumeration when the object is
instantiated. For more information about the enumerations see
<a href="../implementation_strategies/type_handling/static_fields_and_enums.html" class="wikiLink">Static Fields And Enums</a>.</p>
<p>This approach allows to save database space and proves to be
efficient. However, if you are looking at an enumeration object using
ObjectManager, the enumeration will be constructed as a generic object,
therefore the binding procedure won't be triggered. This will affect the
following:</p>
<ul><li>enumeration
type fields will show the class name instead of the actual values, for
example "com.examples.Colors" instead of "Red", "Green" etc.;</li><li>you
won't be able to constrain queries on the enumeration field values;</li><li>you
won't see "name" and "ordinal" field values querying for the enumeration
type data.</li></ul>
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This revision (1) was last Modified 2007-08-11T14:57:01 by Tetyana.
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