JPQL

With the Java Persistence Query Language the persistence objects graph can be queried, in a similar way to querying a database by using SQL, and it looks just like that.

SELECT c FROM Customer c JOIN c.orders o WHERE c.status = 1 AND o.totalPrice > 10000

Values Placeholders

Queries can contain variables, which are swapped by actual values when executing the query.

In this example there is a variable named id:

SELECT entity FROM SimpleEntity entity WHERE entity.id = :id

Executing queries

A query can be executed with a javax.persistence.EntityManager.

String query = "SELECT entity FROM SimpleEntity entity WHERE entity.id = :id";
Query query = entityManager.createQuery(query);

query.setParameter("id", id);

// Returns the entity
query.getSingleResult();

Integration

JPQL can be used by any JPA implementation, replacing other query languages.

Differences Between Implementations

Note that some implementations may give problems with certain operations. Changing from one JPA provider to another, or switching from a JDBC to another may cause unexpected issues.

For example this query works with Eclipselink:

SELECT entity FROM CollectionEntity entity WHERE :value IN (entity.values)

But will fail with Hibernate, which requires this one:

SELECT entity FROM CollectionEntity entity WHERE :value IN ELEMENTS(entity.values)

More Information

• JPQL Language Reference

• JPA Queries

• Ultimate Guide to JPQL Queries with JPA and Hibernate