hibernate笔记，500页

JTA:  With  default  settings,  it’s  also  your  responsibility  to  flush()  each  Session
manually  to  synchronize  it  with  the  database 

Think  about  the  relationship between User and BillingDetails, a one-to-many entity association: If a Credit-
Card is modified, the version of the related User isn’t incremented. If you add or
remove a CreditCard (or BankAccount) from the collection of billing details, the
version of the User is incremented.