title: Replacing existing rows with new ones causes duplicate key exception
body: <p>everyone.
  I have problem replacing existing rows in table with new ones. I use JPA and PostgreSQL DB. I'm trying to delete all existing rows and then create new ones, but receive exception:
  org.postgresql.util.PSQLException: ERROR: duplicate key value violates unique constraint "user_destination_pk". All these actions are inside single JTA transaction. It seems that JPA doesn't delete rows before inserting, but I receive no delete exception... Any help is appreciated.</p>