JPA: Retrieving ID of Recently Persisted Object

Using JPA with an orm.xml, I was having trouble retrieving the primary key (id) of a recently persisted object. The entity in my orm.xml:

<entity class="Foo" name="Foo" access="FIELD">
 <table name="Foo"/>
 <attributes>
   <id name="id">
     <column name="ID" nullable="false"/>
     <generated-value strategy="SEQUENCE"/>
   </id>
   ...
  </table>
</entity>

The relevant MySQL for the table:

CREATE TABLE FOO
(
  ID       INT              NOT NULL AUTO_INCREMENT,
...
  PRIMARY KEY(ID)
)

Regardless of whether or not the id property was null or not, it was not updated after the following call to persist():

Foo foo = new Foo();
getJpaTemplate().persist(foo);
if (logger.isDebugEnabled())
  logger.debug(foo.getId()) // null

Adding a call to flush() however ended up giving me the id:

Foo foo = new Foo();
getJpaTemplate().persist(foo);
getJpaTemplate().flush();
if (logger.isDebugEnabled())
  logger.debug(foo.getId()) // outputs the assigned id

I'm not sure why the flush() was necessary. A similar issue is also discussed here: Spring Forums Post.