bikeshed/src/META-INF/persistence.xml

<?xml version="1.0" encoding="UTF-8" ?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
        http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd" version="1.0">

    <persistence-unit name="transactions-optional">
        <provider>org.datanucleus.store.appengine.jpa.DatastorePersistenceProvider</provider>
        <class>com.google.gwt.sample.expenses.server.domain.Employee</class>
        <class>com.google.gwt.sample.expenses.server.domain.Expense</class>
        <class>com.google.gwt.sample.expenses.server.domain.Report</class>
        <class>com.google.gwt.sample.expenses.server.domain.EntityCounter</class>
        <exclude-unlisted-classes>true</exclude-unlisted-classes>
        <properties>
            <property name="datanucleus.NontransactionalRead" value="true"/>
            <property name="datanucleus.NontransactionalWrite" value="true"/>
            <property name="datanucleus.ConnectionURL" value="appengine"/>
        </properties>
    </persistence-unit>

</persistence>