Why am I getting \"different object with the same identifier value was already associated with the session\" error in myHibernate many-to-many mapping?

Hibernate Different Identifier Error in Many-to-Many Mapping

The error "different object with the same identifier value was already associated with the session" occurs when Hibernate tries to save an object that already exists in the session. In this case, it appears to be related to a many-to-many mapping involving UserBean, GroupBean, and RoleBean classes.

In the provided code, the issue seems to arise when the saveOrUpdate method is used within the save function. saveOrUpdate attempts to both save and update objects, and in this case, it's encountering a duplicate rolebean#1 object.

The error suggests two possible solutions:

• Use session.merge(e) instead of session.saveOrUpdate(e): This method merges the detached object with the persistent object, avoiding the identifier conflict. However, it also has the potential to overwrite existing data.
• Identify the cause of the duplicate rolebean#1 object: Inspect the code where the role bean is assigned to both the user and the group and determine if there's an issue with how the instances are being created or assigned.

The exception message indicates that the rolebean#1 object has been saved twice in the session, which could occur if the same object is assigned to multiple collections (userbean.groups and userbean.roles) without being marked as a new instance in each case.

By understanding the Hibernate behavior and examining the code where the objects are assigned, it's possible to resolve the issue and ensure that the objects are saved and associated correctly within the session.

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