What is the difference between save() and merge() in Hibernate?
Save and merge are two methods in Hibernate that are used to persist entities in the database. However, they have different purposes and implications:
1. Save: The save method is used to insert a new entity into the database. It generates a new ID for the entity and sets its state to persistent. If the entity already exists in the database, an exception is thrown.
2. Merge: The merge method is used to update an existing entity in the database or insert a new entity if it does not already exist. Unlike save, merge does not generate a new ID for the entity and does not change its state to persistent. Instead, it returns a managed entity that is in sync with the state of the database.
In summary, save is used for inserting new entities, while the merge is used for updating existing entities or inserting new entities if they do not exist.