What is fetch in JPA?

JPA FetchType A JPA association can be fetched lazily or eagerly. The fetching strategy is controlled via the fetch attribute of the @OneToMany , @OneToOne , @ManyToOne , or @ManyToMany . The fetch attribute can be either FetchType. LAZY or FetchType.

What is Criteria query in Java?

The Criteria API is used to define queries for entities and their persistent state by creating query-defining objects. Criteria queries are written using Java programming language APIs, are typesafe, and are portable. Such queries work regardless of the underlying data store.

How do you use JPA criteria?

Let’s see it step by step:

  1. Create an instance of Session from the SessionFactory object.
  2. Create an instance of CriteriaBuilder by calling the getCriteriaBuilder() method.
  3. Create an instance of CriteriaQuery by calling the CriteriaBuilder createQuery() method.

What is fetch type?

The FetchType defines when Hibernate gets the related entities from the database, and it is one of the crucial elements for a fast persistence tier. In general, you want to fetch the entities you use in your business tier as efficiently as possible.

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 Criteria query in Hibernate?

The Hibernate Criteria Query Language (HCQL) is used to fetch the records based on the specific criteria. The Criteria interface provides methods to apply criteria such as retreiving all the records of table whose salary is greater than 50000 etc.

What is the difference between query and criteria in Hibernate?

HQL is suitable for executing Static Queries, where as Criteria is suitable for executing Dynamic Queries. HQL is to perform both select and non-select operations on the data, Criteria is only for selecting the data, we cannot perform non-select operations using criteria.

What are the two types of fetch strategies in JPA do you know?

Both FetchType. LAZY and FetchType. EAGER are used to define the default fetch plan.

What is eager fetch?

Eager fetching is the ability to efficiently load subclass data and related objects along with the base instances being queried.

What is fetch select?

fetch-“select” (default) = Load all the collections and entities in a separate query from the parent entity. With eager loading, this will result in N+1 queries being issued for N entities; with lazy loading, the query to load each collection will be issued later, when the collection is accessed.

What is fetch strategy?

Hibernate uses a fetching strategy to retrieve associated objects if the application needs to navigate the association. Fetch strategies can be declared in the O/R mapping metadata, or over-ridden by a particular HQL or Criteria query.