Hibernate throws MultipleBagFetchException - cannot simultaneously fetch multiple bags

2025-01-26 (Last Modified: 2025-01-26)

Fetching aggregate collections from a database tin beryllium a tough concern, particularly once utilizing an Entity-Relational Mapping (ORM) implement similar Hibernate. 1 communal pitfall that builders brush is the dreaded MultipleBagFetchException. This objection happens once Hibernate makes an attempt to burden aggregate “luggage” (unindexed collections, similar Database) from the aforesaid entity successful a azygous question. Knowing wherefore this occurs and however to resoluteness it is important for businesslike information retrieval and a creaseless-moving exertion. This article dives heavy into the causes of the MultipleBagFetchException, gives applicable options, and provides champion practices to debar this content altogether.

Knowing the MultipleBagFetchException

Hibernate makes use of anxious loading by default for collections, which means it tries to retrieve each associated information astatine erstwhile. Piece handy, this tin pb to the MultipleBagFetchException once an entity has aggregate postulation-valued properties, specified arsenic 2 oregon much Database fields. The underlying job is that SQL doesn’t person a cleanable manner to correspond aggregate collections successful a azygous consequence fit, inflicting Hibernate to battle with mapping the information backmost to the accurate objects.

Ideate querying for a Buyer entity with 2 lists: orders and addresses. Hibernate makes an attempt to harvester the outcomes into a azygous question, which leads to Cartesian merchandise points, wherever all command is related with all code, ensuing successful an incorrect and frequently monolithic dataset. This is wherefore Hibernate throws the MultipleBagFetchException, defending you from surprising and possibly dangerous behaviour.

This content arises about generally with older variations of Hibernate, although equal successful the newest variations, knowing the underlying ideas is cardinal for optimum show.

Options and Workarounds

Respective methods tin aid you flooded the MultipleBagFetchException. Selecting the correct attack relies upon connected your circumstantial wants and the complexity of your information exemplary. 1 communal resolution is to control from anxious loading to lazy loading for 1 oregon much of the collections. This tells Hibernate to lone burden the postulation once it’s explicitly accessed.

Lazy Loading: Adhd fetch = FetchType.LAZY to the problematic postulation mappings successful your entity people. This delays the loading of the postulation till it’s really wanted.
HQL/JPQL Joins: Usage express joins successful your HQL oregon JPQL queries to power which collections are fetched. This gives much granular power complete the information retrieval procedure.

Different effectual attack is to usage subqueries oregon abstracted queries to fetch all postulation individually. This whitethorn addition the figure of database queries however avoids the Cartesian merchandise job and ensures close outcomes.

Fetch the chief entity archetypal.
Past, execute abstracted queries for all postulation, utilizing the ID of the chief entity to filter the outcomes.

Champion Practices for Fetching Collections

Selecting the correct fetching scheme is important for show. Complete-anxious fetching tin pb to the MultipleBagFetchException and show bottlenecks, piece extreme lazy loading tin consequence successful the N+1 job. Cautiously see your entree patterns and take the attack that champion balances show and information consistency.

For case, if you about ever demand some collections once retrieving the chief entity, utilizing abstracted queries oregon HQL joins mightiness beryllium the about businesslike action. Nevertheless, if 1 postulation is seldom accessed, lazy loading is the most well-liked attack.

Utilizing DTOs (Information Transportation Objects) tin besides beryllium generous. DTOs let you to retrieve lone the essential information, minimizing the overhead related with fetching full entities and their related collections. This attack is particularly utile successful analyzable situations wherever you demand to harvester information from aggregate entities and collections.

Hibernate Tuning and Optimization

Optimizing your Hibernate configuration tin importantly better show and aid debar points similar the MultipleBagFetchException. See utilizing a 2nd-flat cache to trim database hits and better consequence instances. Moreover, configuring batch fetching permits Hibernate to retrieve aggregate entities oregon collections successful a azygous question, minimizing the figure of circular journeys to the database.

Batch fetching tin beryllium peculiarly effectual once dealing with ample collections, arsenic it importantly reduces the overhead of idiosyncratic queries. Nevertheless, beryllium aware of the batch dimension; overly ample batches tin devour extreme representation and negatively contact show. Experimentation and profiling are cardinal to uncovering the optimum equilibrium for your circumstantial usage lawsuit.

FAQ

Q: What’s the chief origin of the MultipleBagFetchException?

A: Making an attempt to eagerly fetch aggregate unordered collections (similar Database) for a azygous entity successful 1 question. SQL’s limitations successful dealing with aggregate collections successful a azygous consequence fit lend to this.

By knowing the underlying causes of the MultipleBagFetchException and implementing the options outlined supra, you tin efficaciously negociate collections successful your Hibernate entities and physique businesslike, advanced-performing purposes. See your entree patterns, optimize your queries, and tune your Hibernate configuration for the champion outcomes. Retrieve to prioritize lazy loading once imaginable and strategically make the most of HQL joins oregon abstracted queries for much analyzable situations. This proactive attack not lone avoids irritating exceptions however besides ensures optimum information retrieval and a creaseless person education. Research further assets connected Hibernate champion practices and show tuning to additional heighten your abilities.

Additional investigation into Hibernate’s fetching methods, HQL optimization, and the effectual usage of DTOs volition supply a deeper knowing of managing analyzable entity relationships. Dive deeper into these subjects to refine your Hibernate experience and physique sturdy, performant functions.

Question & Answer :
Hibernate throws this objection throughout SessionFactory instauration:

org.hibernate.loader.MultipleBagFetchException: can’t concurrently fetch aggregate baggage

This is my trial lawsuit:

Genitor.java

@Entity national Genitor { @Id @GeneratedValue(scheme=GenerationType.Individuality) backstage Agelong id; @OneToMany(mappedBy="genitor", fetch=FetchType.Anxious) // @IndexColumn(sanction="INDEX_COL") if I had this the job lick however I retrieve much kids than I person, 1 kid is null. backstage Database<Kid> youngsters; }

Kid.java

@Entity national Kid { @Id @GeneratedValue(scheme=GenerationType.Individuality) backstage Agelong id; @ManyToOne backstage Genitor genitor; }

However astir this job? What tin I bash?

EDIT

Fine, the job I person is that different “genitor” entity is wrong my genitor, my existent behaviour is this:

Genitor.java

@Entity national Genitor { @Id @GeneratedValue(scheme=GenerationType.Individuality) backstage Agelong id; @ManyToOne backstage AnotherParent anotherParent; @OneToMany(mappedBy="genitor", fetch=FetchType.Anxious) backstage Database<Kid> kids; }

AnotherParent.java

@Entity national AnotherParent { @Id @GeneratedValue(scheme=GenerationType.Individuality) backstage Agelong id; @OneToMany(mappedBy="genitor", fetch=FetchType.Anxious) backstage Database<AnotherChild> anotherChildren; }

Hibernate doesn’t similar 2 collections with FetchType.Anxious, however this appears to beryllium a bug, I’m not doing different issues…

Deleting FetchType.Anxious from Genitor oregon AnotherParent solves the job, however I demand it, truthful existent resolution is to usage @LazyCollection(LazyCollectionOption.Mendacious) alternatively of FetchType (acknowledgment to Bozho for the resolution).

I deliberation a newer interpretation of hibernate (supporting JPA 2.zero) ought to grip this. However other you tin activity it about by annotating the postulation fields with:

@LazyCollection(LazyCollectionOption.Mendacious)

Retrieve to distance the fetchType property from the @*ToMany annotation.

However line that successful about circumstances a Fit<Kid> is much due than Database<Kid>, truthful until you truly demand a Database - spell for Fit

Usage with warning

Retrieve that utilizing a Fit gained’t destroy the underlying Cartesian Merchandise arsenic described by Vlad Mihalcea successful his reply, featured arsenic “The worst resolution”!