Java Persistence Query Language

Java Persistence Query Language
Класс языка	язык запросов
Появился в	2009
Испытал влияние	SQL
Сайт	eclipse-ee4j.github.io/j…

Java Persistence Query Language (JPQL) — платформо-независимый объектно-ориентированный язык запросов defined as part of the 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, but operate against JPA entity objects rather than directly with database tables.

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

Примеры

Suppose we have JPA entity classes defined like this (getter and setter methods omitted for simplicity):

@Entity
public class Author {
    @Id
    private Integer id;
    private String firstName;
    private String lastName;
    
    @ManyToMany
    private List<Book> books;
}

@Entity
public class Book {
    @Id
    private Integer id;
    private String title;
    private String isbn;
    
    @ManyToOne
    private Publisher publisher;
    
    @ManyToMany
    private List<Author> authors;
}

@Entity
public class Publisher {
    @Id
    private Integer id;
    private String name;
    private String address;

    @OneToMany(mappedBy = "publisher")
    private List<Book> books;
}

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

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

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

SELECT DISTINCT a FROM Author a INNER JOIN a.books b WHERE b.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:

import javax.persistence.EntityManager;
import javax.persistence.Query;
import org.apache.commons.lang.StringUtils;

...

@SuppressWarnings("unchecked")
public List<Author> getAuthorsByLastName(String lastName) {
    String queryString = "SELECT a FROM Author a " +
                         "WHERE :lastName IS NULL OR LOWER(a.lastName) = :lastName";
    Query query = getEntityManager().createQuery(queryString);
    
    query.setParameter("lastName", StringUtils.lowerCase(lastName));
    return query.getResultList();
}

Hibernate Query Language

JPQL is based on the Hibernate Query Language (HQL), an earlier non-standard query language included in the 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.

См. также

• Object-relational mapping
• Hibernate (Java)
• Java Persistence API

Ссылки

• Full Query Language Syntax from The Java EE 5 Tutorial  (англ.)
• JPA Queries and JPQL — a chapter of the ObjectDB Manual  (англ.)
• Type safe Hibernate (HQL) query engine — TorpedoQuery  (англ.)

Категория:Информационные языки Категория:Data modeling languages Категория:Java Enterprise Edition