How to Solve the Hibernate Error: NonUniqueObjectException?

Hibernate Error: Non-Unique Object Exception

When attempting to save objects using Hibernate, you may encounter the "org.hibernate.NonUniqueObjectException," indicating that an object with the same identifier is already associated with the session.

This error arises when you have two distinct objects with the same primary key. Hibernate identifies objects using their primary key values, and if two objects share the same key, Hibernate assumes they are the same object. However, in this case, they are distinct entities.

The error message often appears when there's a cascading save between two objects, and one of them (Object B) is already associated with the session but not on the same instance as the one on Object A.

Potential Causes:

One possible cause is the use of a database-generated primary key generator. In this scenario, if an object is removed from the database and then recreated with the same primary key, it will conflict with the existing object in the persistent context during saving.

Another potential cause is if you have updated or removed values in a table that is referenced by other objects. Upon attempting to reinsert those objects, the existing objects will throw an exception.

Suggestions for Resolution:

To resolve this error:

• Double-check your code: Review your cascade settings and ensure that objects are attached to the session correctly.
• Confirm your primary key generator: Choose a suitable primary key generation strategy to avoid conflicts with existing database records.
• Consider using pessimistic locking: This can ensure that multiple threads are not modifying the same object concurrently.
• Reset the persistent context: If the error persists, you can try clearing the persistent context by calling session.clear(). However, this may cause unintended side effects.

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