public class EmbeddedTest extends TestCase {
   
   private EntityManagerFactory emf;
   private EntityManager em;
   private EntityTransaction tx;
   
   protected void setUp() throws Exception {
      super.setUp();
      
      emf = Persistence.createEntityManagerFactory("TEST_SE", map);
   }

   protected void tearDown() throws Exception {
   }

   public void testEmbedded() {
      em = emf.createEntityManager();

      tx = em.getTransaction();
      tx.begin();
      Container c = new Container();

      // persist container entity with no containee
      em.persist(c);

      tx.commit();
      
      int id = c.id;
      
      c = em.find(Container.class, id);

      // implicitely detach c by closing and reopening entitymanager
      em.close();
      em = emf.createEntityManager();

      // manipulate detached c
      c.containee = new Containee();
      
      tx = em.getTransaction();
      tx.begin();
      
      // merge c into persistent context
      Container cMerged = em.merge(c);
      
      /*
       * gives:
       *
       *javax.persistence.PersistenceException: org.hibernate.PropertyAccessException: could not get a field value by reflection getter of de.regiogmbh.inecos.framework.Embedee.string
       *
       **/

      tx.commit();

      em.close();
   }
}

@Entity
@AccessType("field")
@Table(
      name="container"
)
public class Container {

   @Id
   @GeneratedValue
   int id;

    @OneToOne(cascade=CascadeType.ALL,fetch=FetchType.EAGER,optional=true)
    Containee containee;

}

@Entity
@Table(
      name="containee"
)
public class Containee {
   
   @SuppressWarnings("unused")
   @Id
   @GeneratedValue
   int id;
   
   @Embedded
   Embedee embedee;

}

@Embeddable
@AccessType("field")
public class Embedee {
   
   String string = "string";

}

<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="TEST_SE" transaction-type="RESOURCE_LOCAL">
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
    <class>Container</class>
    <class>Containee</class>
    <exclude-unlisted-classes>true</exclude-unlisted-classes>
    <properties>
      <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5InnoDBDialect" />
      <property name="hibernate.max_fetch_depth" value="2" />
      <property name="hibernate.show_sql" value="true" />
      <property name="hibernate.use_sql_comments" value="true" />
      <property name="hibernate.hbm2ddl.auto" value="create-drop" />
      <property name="hibernate.ejb.autodetection" value="none" />
      <property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver" />
      <property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/test" />
      <property name="hibernate.connection.username" value="..." />
      <property name="hibernate.connection.password" value="..." />
      <property name="hibernate.connection.provider_class" value="org.hibernate.connection.C3P0ConnectionProvider" />
      <property name="c3p0.acquire_increment" value="3" />
      <property name="c3p0.idle_test_period" value="300" />
      <property name="c3p0.initialPoolSize" value="10" />
      <property name="c3p0.min_size" value="15" />
      <property name="c3p0.max_size" value="50" />
      <property name="c3p0.timeout" value="1800" />
      <!--  -->
      <property name="hibernate.cache.provider_class" value="net.sf.ehcache.hibernate.EhCacheProvider" />
    </properties>
  </persistence-unit>
</persistence>