How to Resolve Hibernate's NonUniqueObjectException: A Detailed Guide

Hibernate NonUniqueObjectException: Resolving Persistent State Conflicts

Encountering the org.hibernate.NonUniqueObjectException while saving Hibernate objects can be puzzling. This exception occurs when Hibernate detects that an object with the same identifier as the one being persisted is already associated with the current session.

To address this issue, it's crucial to understand Hibernate's persistent state management. Hibernate tracks the persistent state of objects based on their identifier values. If multiple objects have the same identifier, Hibernate considers them to be the same object, even if they are distinct instances. This can lead to conflicts when attempting to save or update objects.

In the provided code snippet, it's evident that userObj1 and userObj2 have the same identifier value. This could be due to cascading saves or manual object manipulation. To resolve this issue, it's essential to trace the code and identify the source of the identifier collision.

One possible cause is the use of the session.save() method without ensuring that the objects are not already attached to the session. Hibernate saves an object only if it's not already persistent. Attempting to save an attached object will result in the exception.

Another potential issue is related to the primary key generator. Specific generators may require manual assignment of identifier values, which can lead to conflicts if not handled correctly.

If you are experiencing this exception, it's recommended to:

• Break down the code and analyze the flow to identify where the identifier collision occurs.
• Check the primary key generator and ensure it assigns unique identifier values.
• Consider using Hibernate's sessionFactory.getCurrentSession() method to obtain the current session, which can help maintain proper session state.
• If possible, cascade saves should be used谨慎行事，以避免意外冲突。

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