DataNucleus - Plugins : Identity String Translators

DataNucleus is developed as a plugin-driven framework and one of the components that is pluggable is translation of identities. When you call pm.getObjectById(id) you pass in an object. This object can be the toString() form of an identity. Some other JDO implementations (e.g Xcalia) allowed non-standard String input here including a discriminator. This plugin point allows for such non-standard String input forms to pm.getObjectById(id) and can provide a plugin that translates this String into a valid JDO identity. Alternatively you could do this in your own code, but the facility is provided. This means that in your application you only use your own form of identities.

You can extend DataNucleus's capabilities using the plugin extension org.datanucleus.identity_string_translator .

Plugin extension-point	Key	Description	Location
org.datanucleus.identity_string_translator	xcalia	Translator that allows for {discriminator}:key as well as the usual input, as supported by Xcalia XIC	datanucleus-core

Interface

Any identifier factory plugin will need to implement org.datanucleus.store.IdentifierStringFactory . So you need to implement the following interface

package org.datanucleus.identity;

public interface IdentityStringTranslator
{
    /**
     * Method to translate the string into the identity.
     * @param om ObjectManager
     * @param stringId String form of the identity
     * @return The identity
     */
    Object getIdentity(ObjectManager om, String stringId);
}

Plugin Specification

When we have defined our "IdentityStringTranslator" we just need to make it into a DataNucleus plugin. To do this you simply add a file plugin.xml to your JAR at the root. The file plugin.xml should look like this

<?xml version="1.0"?>
<plugin id="mydomain" name="DataNucleus plug-ins" provider-name="My Company">
    <extension point="org.datanucleus.identity_string_translator">
        <identitystringtranslator name="mytranslator" class-name="mydomain.MyIdStringTranslator"/>
    </extension>
</plugin>

Note that you also require a MANIFEST.MF file as per the Plugins Guide.

Plugin Usage

The only thing remaining is to use your new IdentityStringTranslator plugin. You do this by having your plugin in the CLASSPATH at runtime, and setting the persistence property datanucleus.identityStringTranslatorType to mytranslator (the name you specified in the plugin.xml file).