How to Resolve Hibernate's MultipleBagFetchException?

MultipleBagFetchException in Hibernate

When attempting to create a SessionFactory in Hibernate, users may encounter the exception:

org.hibernate.loader.MultipleBagFetchException: cannot simultaneously fetch multiple bags

This error arises when trying to simultaneously fetch multiple collections of entities that are mapped with FetchType.EAGER.

To resolve this issue, consider the following:

1. Check Hierarchical Entity Relationships: If the entities have a hierarchical relationship, such as a parent entity referencing multiple child entities, ensure that the fetch type is set correctly for each level. Avoid eager fetching for both parent and child collections as it can lead to performance issues and exceptions.
2. Use @LazyCollection Annotation: An alternative solution is to utilize the @LazyCollection(LazyCollectionOption.FALSE) annotation on the collection field, which effectively overrides the fetch type. Remember to remove the fetchType attribute from the @OneToMany or @ManyToMany annotations.
3. Set Data Structures: Consider using a Set instead of List, as sets typically provide better performance and avoid duplicates.

Caution:

Using sets does not eliminate the risk of Cartesian products, as eagerly fetching collections can still lead to excessive data retrieval.

The above is the detailed content of How to Resolve Hibernate's MultipleBagFetchException?. For more information, please follow other related articles on the PHP Chinese website!