Why am I Getting a org.hibernate.NonUniqueObjectException Despite Using session.clear()?

Non-Unique Objects in Hibernate: Understanding the org.hibernate.NonUniqueObjectException

When saving objects using Hibernate, you may encounter the following error:

Caused by: org.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session:
[com.pojo.rtrequests.User#com.pojo.rtrequests.User@d079b40b]

This error indicates that the session already contains an object with the same identifier (primary key) as the object you are attempting to save. Despite using session.clear(), the problem persists, leaving you wondering why this issue arises.

Root Cause and Solution

The root cause of this error is the presence of two separate objects with the same identifier but as distinct instances. This typically occurs when cascaded saves are involved, where object A has a cascade save relationship with object B, but object B is already associated with the session as a different instance than the one referenced by object A.

To resolve this issue, it's important to identify the primary key generator being used. The error is related to Hibernate's mechanism for determining an object's persistent state. If the generator attempts to persist an object that is already persistent, it will raise this exception.

Additional Considerations

In certain scenarios, the error can be triggered when data has been removed or modified in a table related to the objects being saved. For example, if you attempt to re-insert values that were previously deleted, this can result in a NonUniqueObjectException.

Debugging Tips

To debug and resolve this issue, consider the following steps:

• Break down your code and comment out sections until the error disappears. This will help you isolate the problematic code.
• Check the instances of objects involved in cascaded saves to ensure that they are the same.
• Examine the primary key generation strategy to understand how Hibernate is assigning identifiers.
• If necessary, verify whether any data has been manipulated in related tables that could cause unique key conflicts.

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