Why Am I Getting a 'org.hibernate.NonUniqueObjectException' in My Hibernate Application?

Exploring Hibernate Error: "org.hibernate.NonUniqueObjectException"

The error encountered, "org.hibernate.NonUniqueObjectException," arises when Hibernate encounters two distinct objects with identical identifiers associated with the same session. This discrepancy often points to a deeper issue in the code.

From the provided code snippet, it seems that two User objects, userObj1 and userObj2, are being saved into the session using rtsession.save(). However, Hibernate is rejecting this operation because it considers the given user object to be already associated with the session.

This error typically occurs due to one of two reasons:

1. Incorrectly Cascading Objects: If there are any cascade relationships defined between object A and object B, this error can arise if object B has been previously associated with the session but is not the same instance as the one being referenced by object A.
2. Primary Key Generator Issue: The error may also be linked to the primary key generator being used. If Hibernate attempts to persist an object that is already persistent, this conflict can trigger the "NonUniqueObjectException."

To resolve this issue, it is recommended to carefully examine the code and identify where the duplication of objects occurs. Breaking down the code, commenting out certain sections until the error disappears, and then gradually reinstating the code until the error recurs can help pinpoint the culprit. Additionally, reviewing the primary key generator and ensuring proper object association can aid in resolving this issue.

Furthermore, consider the following troubleshooting tips:

• Check if you have recently updated or removed any values in a table that is part of a relationship.
• Verify if you are attempting to insert the same objects again after performing a previous update or removal operation.
• Use Hibernate's detach() method to remove the object from the session before re-attaching it with saveOrUpdate().
• If all else fails, refer to Hibernate documentation for more detailed guidance and error-handling strategies.

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