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| Jakarta Persistence Query Language | |
|---|---|
| OS | Cross-platform |
| Website | eclipse-ee4j |
| Influenced by | |
| SQL,Hibernate | |
TheJakarta Persistence Query Language (JPQL; formerly Java Persistence Query Language) is a platform-independentobject-orientedquery language[1]: 284, §12 defined as part of theJakarta Persistence (JPA; formerly Java Persistence API) specification.
JPQL is used to make queries against entities stored in a relational database. It is heavily inspired bySQL, and its queries resemble SQL queries in syntax,[1]: 17, §1.3 but operate against JPA entity objects rather than directly with database tables.[1]: 26, §2.2.3
In addition to retrieving objects (SELECT queries), JPQL supports set basedUPDATE andDELETE queries.
Example JPA Classes, getters and setters omitted for simplicity.
@EntitypublicclassAuthor{@IdprivateIntegerid;privateStringfirstName;privateStringlastName;@ManyToManyprivateList<Book>books;}@EntitypublicclassBook{@IdprivateIntegerid;privateStringtitle;privateStringisbn;@ManyToOneprivatePublisherpublisher;@ManyToManyprivateList<Author>authors;}@EntitypublicclassPublisher{@IdprivateIntegerid;privateStringname;privateStringaddress;@OneToMany(mappedBy="publisher")privateList<Book>books;}
Then a simple query to retrieve the list of all authors, ordered alphabetically, would be:
SELECTaFROMAuthoraORDERBYa.firstName,a.lastName
To retrieve the list of authors that have ever been published by XYZ Press:
SELECTDISTINCTaFROMAuthoraINNERJOINa.booksbWHEREb.publisher.name='XYZ Press'
JPQL supports named parameters, which begin with the colon (:). We could write a function returning a list of authors with the given last name as follows:
importjavax.persistence.EntityManager;importjavax.persistence.TypedQuery;...publicList<Author>getAuthorsByLastName(StringlastName){StringqueryString="SELECT a FROM Author a "+"WHERE a.lastName IS NULL OR LOWER(a.lastName) = LOWER(:lastName)";TypedQuery<Author>query=getEntityManager().createQuery(queryString,Author.class);query.setParameter("lastName",lastName);returnquery.getResultList();}
JPQL is based on theHibernate Query Language (HQL), an earlier non-standard query language included in theHibernateobject-relational mapping library.
Hibernate and the HQL were created before the JPA specification.As of Hibernate 3 JPQL is a subset of HQL.
