samples/mobilewebapp/src/main/java/META-INF/persistence.xml

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.0"
	xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd">
	<persistence-unit name="transactions-optional">
		<provider>org.datanucleus.store.appengine.jpa.DatastorePersistenceProvider</provider>
		<properties>
			<property name="datanucleus.NontransactionalRead" value="true" />
			<property name="datanucleus.NontransactionalWrite" value="true" />
			<property name="datanucleus.ConnectionURL" value="appengine" />
		</properties>
	</persistence-unit>
</persistence>