[java] What is the difference between persist() and merge() in JPA and Hibernate?

The most important difference is this:

  • In case of persist method, if the entity that is to be managed in the persistence context, already exists in persistence context, the new one is ignored. (NOTHING happened)

  • But in case of merge method, the entity that is already managed in persistence context will be replaced by the new entity (updated) and a copy of this updated entity will return back. (from now on any changes should be made on this returned entity if you want to reflect your changes in persistence context)

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