= Enhancer (DataNucleus)

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A responsibility of all ORMs is lazy loading of related objects (so as not to load all the data in one go), and tracking of objects as they are modified (to flush back to the database).

With JDO, this is accomplished by post-processing -- or _enhancing_ -- the compiled bytecode.

This is typically performed using the `datanucleus:enhance` Maven plugin.
This is defined as the `isis-app-starter-datanucleusenhance` profile in the xref:docs:parent-pom:about.adoc[Parent POM], and is activated by the presence of the `logging-dn-enhance.properties` file.

[source,xml]
.App Starter Parent POM (pom.xml)
----
<profile>
  <id>isis-app-starter-datanucleusenhance</id>
  <activation>
    <file>
	  <exists>${basedir}/logging-dn-enhance.properties</exists>
    </file>
  </activation>
  <build>
    <plugins>
      <plugin>
        <groupId>org.datanucleus</groupId>
        <artifactId>datanucleus-maven-plugin</artifactId>
        ..
      </plugin>
    </plugins>
  </build>
<profile>
----

Some IDEs (notably Eclipse) provide plugins to run the enhancer as part of their compile process.
See xref:setupguide:ROOT:about.adoc[setup guides] for more details.
