Updating seam entity causing: "Another user changed the same data, please try again"

[bedek_bedkowski]

Hi,

I've problem executing this piece of code in Stateful seam component:

// create new entity object
Car myCar = new Car();
myCar.setType("van");

// save entity for a first time - entity is save correctly in database
log.debug("Saving car: " + myCar);
entityManager.persist(myCar);

// update entity member parameter
myCar.setType("truck");
log.debug("Changing car type to: " + myCar);

// flush manager - maybe not needed ?
log.debug("Flushing manager");
entityManager.flush();

// saving updated entity - this one is causing exception: "Another user changed the same data, please try again"
log.debug("Saving changed car : " + myCar);
entityManager.persist(myCar);

As result in log file I can find error mesage:

org.hibernate.event.def.AbstractFlushingEventListener: Could not synchronize database state with session

and in the bowser this message appears:

Another user changed the same data, please try again

My question is:
Entity is created in database but updated causes exception - how to perform this action ?