Hibernate Exception: \"Same Identifier Value Associated with Session\" - How to Avoid This Common Error?

Hibernate Exception: 'Same Identifier Value Associated with Session'

When attempting to update an entity using the session's SaveOrUpdate method, you may encounter the following exception:

Hibernate: different object with the same identifier value was already associated with the session

This exception indicates that another instance of the same entity, having the same identifier value, has already been associated with the session. This conflict arises when you try to save or update an entity that has previously been modified and saved independently.

To resolve this issue, consider the following options:

1. Using merge() Instead of SaveOrUpdate():

Replacing saveOrUpdate() with merge() will resolve the conflict because merge() assumes the detached entity should be reattached and merged into the session. However, this approach may not work if you want to explicitly save or update the entity.

2. Identifying the Conflicting Instance:

To find the conflicting instance, inspect the code where the entity is assigned or modified. Check for multiple instances of the same entity being associated with different objects or collections.

3. Using a Different Flush Strategy:

If both saveOrUpdate() and merge() cause problems, consider using a different flush strategy. By manipulating the FlushMode of the session or entity manager, you can control when and how the changes are flushed to the database. This may help prevent the conflict.

Example:

In the provided example, when the saveOrUpdate() method is used to save a UserBean instance, the following sequence occurs:

• Group beans and their roles are saved.
• Role beans associated with the user's roles are then saved.

Since role beans are shared between multiple objects, the second save attempt for the same role bean results in the conflict. To resolve this, you could either use merge() to attach the modified role bean or identify the conflicting association and modify it to use a single instance of the role bean.

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