can't operate on multiple entity groups in a single transaction.

Caused by: javax.persistence.PersistenceException: Illegal argument
	at org.datanucleus.jpa.NucleusJPAHelper.getJPAExceptionForNucleusException(NucleusJPAHelper.java:260)
	at org.datanucleus.jpa.EntityTransactionImpl.commit(EntityTransactionImpl.java:122)
	at org.datanucleus.store.appengine.jpa.DatastoreEntityTransactionImpl.commit(DatastoreEntityTransactionImpl.java:55)
	at org.springframework.orm.jpa.JpaTransactionManager.doCommit(JpaTransactionManager.java:456)
	... 86 more
Caused by: java.lang.IllegalArgumentException: can't operate on multiple entity groups in a single transaction. found both Element {
  type: "Options"
  id: 36
}
 and Element {
  type: "Options"
  id: 37
}

 因为GAE只支持一个事务操作一个实体.

这里讲到了很多GAE开发中的注意点,值得参考:http://www.cnblogs.com/senzjx/archive/2009/09/20/1570669.html