How to Fix Hibernate's PersistentObjectException with Detached Entities?

Correcting PersistentObjectException in Hibernate with Detached Entities

When dealing with JPA-persisted object models, certain operations may result in the PersistentObjectException, particularly when managing relationships. For instance, in the case of a many-to-one relationship between an Account and multiple Transactions, an attempt to persist a Transaction with an already persisted Account may trigger this exception.

Understanding the underlying issue is crucial. When you create a Transaction and specify an existing Account, the Account is considered detached from the entity manager. This occurs because you are retrieving the Account from a different context than the one where the Transaction is being persisted.

To resolve this issue, adjust the cascade type in the Transaction's annotation to CascadeType.MERGE. This ensures that when the Transaction is persisted, the associated Account will be merged into the current entity manager context, resolving the detachment issue.

Here's an updated code snippet:

@Entity
public class Transaction {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @ManyToOne(cascade = {CascadeType.MERGE}, fetch = FetchType.EAGER)
    private Account fromAccount;
}

By implementing these changes, you will be able to successfully persist Transactions with already persisted Accounts, eliminating the PersistentObjectException.

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