How do I fix MultipleBagFetchException?
Option 1: Use a Set instead of a List. The easiest approach to fix the MultipleBagFetchException is to change the type of the attributes that map your to-many associations to a java. util. Set.
Why MultipleBagFetchException?
Cause of MultipleBagFetchException Fetching two or more Bags at the same time on an Entity could form a Cartesian Product. Since a Bag doesn’t have an order, Hibernate would not be able to map the right columns to the right entities. Hence, in this case, it throws a MultipleBagFetchException.
What is fetch in Hibernate?
In general, FetchMode defines how Hibernate will fetch the data (by select, join or subselect). FetchType, on the other hand, defines whether Hibernate will load data eagerly or lazily.
What is @LazyCollection?
We use the @LazyCollection annotation when we need to take care of the performance in our application. Starting from Hibernate 3.0, @LazyCollection is enabled by default. The main idea of using the @LazyCollection is to control whether the fetching of data should be using the lazy approach or the eager one.
What is @OrderColumn?
@OrderColumn annotation specifies a column that should maintain the persistent order of a list. The persistence provider maintains the order and also updates the ordering on insertion, deletion, or reordering of the list. This annotation can be used on @OneToMany or @ManyToMany relationship or on @ElementCollection .
What is lazy true in hibernate?
lazy=”true“ attribute , Meaning : “true” value , is enable lazy loading of the parent and child collections. lazy=false, and hibernate will load the child when parent is loaded from the database.
What is the use of @OrderColumn?
Annotation Type OrderColumn. Specifies a column that is used to maintain the persistent order of a list. The persistence provider is responsible for maintaining the order upon retrieval and in the database.
What is @OrderColumn in hibernate?
@OrderColumn is used to store list index. As list is ordered collection, so to maintain the list index there can be a column in database and while inserting the data, list index will be stored in that column. For this the property in entity should be annotated with. @OrderColumn (name=”column-name”)
What is the multiplebagfetchexception in hibernate?
Hibernate also struggles to differentiate between information that is supposed to be duplicated and information that was duplicated because of the cartesian product. Because of that, Hibernate throws a MultipleBagFetchException. You can find lots of questions about this exception and various solutions to avoid it.
What are some examples of multiplebagfetchexception in Java?
Let’s have some concrete examples that lead to MultipleBagFetchException. For the first example, let’s try to create a simple entity that has 2 bags and both with eager fetch type. An Artist might be a good example. It can have a collection of songs and offers.
Why can’t I fetch more than one bag at a time?
Hibernate doesn’t allow fetching more than one bag because that would generate a Cartesian product. The worst “solution” Now, you will find lots of answers, blog posts, videos, or other resources telling you to use a Setinstead of a Listfor your collections.
Can hibernate fetch multiple collections simultaneously?
Similar to the previous section, this would also generate a cartesian product, which could lead to performance issues. Again, there’s nothing wrong with using a List, Set, or Bag for the data type. The purpose of this section is to demonstrate further that Hibernate can fetch collections simultaneously given there’s no more than one of type Bag.