Jakarta Persistence Query Language: Difference between revisions

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{{norefinline|date=June 2010}}

{{Infobox programming language

| name = JavaJakarta Persistence Query Language

| logo =

| paradigm =

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| latest_test_version =

| latest_test_date =

| turing-complete = No

| typing =

| implementations =

| dialects =

| influenced_by = [[SQL]], [[Hibernate (Java)#Hibernate Query Language (HQL)|Hibernate]]

| influenced =

| operating_system = [[Cross-platform]]

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| website =

}}

The '''JavaJakarta Persistence Query Language''' ('''JPQL'''; formerly Java Persistence Query Language) is a platform-independent [[Object-oriented programming|object-oriented]] [[query language]]{{sfn|Bauer|King|Gregory|2016}}{{rp|loc=§12|p=284}} defined as part of the [[JavaJakarta Persistence API]] (JPA; formerly Java Persistence API) specification.

JPQL is used to make queries against entities stored in a relational database. It is heavily inspired by [[SQL]], and its queries resemble SQL queries in syntax,{{sfn|Bauer|King|Gregory|2016}}{{rp|loc=§1.3|p=17}} but operate against JPA entity objects rather than directly with database tables.{{sfn|Bauer|King|Gregory|2016}}{{rp|loc=§2.2.3|p=26}}

In addition to retrieving objects (<code>SELECT</code> queries), JPQL supports set based <code>UPDATE</code> and <code>DELETE</code> queries.

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Example JPA Classes, getters and setters omitted for simplicity.

<sourcesyntaxhighlight lang="java">

@Entity

public class Author {

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private List<Book> books;

}

</syntaxhighlight>

</source>

Then a simple query to retrieve the list of all authors, ordered alphabetically, would be:

<sourcesyntaxhighlight lang="sql">

SELECT a FROM Author a ORDER BY a.firstName, a.lastName

</syntaxhighlight>

</source>

To retrieve the list of authors that have ever been published by XYZ Press:

<sourcesyntaxhighlight lang="sql">

SELECT DISTINCT a FROM Author a INNER JOIN a.books b WHERE b.publisher.name = 'XYZ Press'

</syntaxhighlight>

</source>

JPQL supports named parameters, which begin with the colon (<code>:</code>). We could write a function returning a list of authors with the given last name as follows:

<sourcesyntaxhighlight lang="java">

import javax.persistence.EntityManager;

import javax.persistence.QueryTypedQuery;

import org.apache.commons.lang.StringUtils;

...

@SuppressWarnings("unchecked")

public List<Author> getAuthorsByLastName(String lastName) {

String queryString = "SELECT a FROM Author a " +

"WHERE :a.lastName IS NULL OR LOWER(a.lastName) = LOWER(:lastName)";

QueryTypedQuery<Author> query = getEntityManager().createQuery(queryString, Author.class);

query.setParameter("lastName", StringUtils.lowerCase(lastName));

return query.getResultList();

}

</syntaxhighlight>

</source>

==Hibernate Query Language==

JPQL is based on the [[Hibernate_Hibernate (Java)#Hibernate_Query_Language_Hibernate Query Language (HQL)|Hibernate Query Language]] (HQL), an earlier non-standard query language included in the [[Hibernate (Java)|Hibernate]] [[object-relational mapping]] library.

Hibernate and the HQL were created before the JPA specification.

As of Hibernate 3 JPQL is a subset of HQL.

==Citations==

{{Reflist}}

==References==

*{{citation

|last1 = Bauer

|first1 = Christian

|last2 = King

|first2 = Gavin

|last3 = Gregory

|first3 = Gary

| year = 2016

| title = Java Persistence with Hibernate

| edition = Second

| publisher = [[Manning Publications]]

| isbn = 978-1617290459

| url =

}}

==See also==

* [[Object-relational mapping]]

* [[Hibernate (Javaframework)]]

* [[JavaJakarta Persistence API]]

== External links ==

* {{official website}}

** [httphttps://docseclipse-ee4j.oraclegithub.com/javaee/6io/jakartaee-tutorial/doc/bnbuf.html#full-query-language-syntax Full Query Language Syntax from The JavaJakarta EE 68 Tutorial]

* [httphttps://www.objectdb.com/java/jpa/query JPA Queries and JPQL - a chapter of the ObjectDB Manual]

* [httphttps://torpedoquery.org/ Type safe Hibernate (HQL) query engine - TorpedoQuery]

{{JavaJakarta Persistence API}}

[[Category:Query languages]]