JPA Queries

Queries are represented in JPA by the Query and TypedQuery interfaces:

• javax.persistence.Query - JPA Interface
• javax.persistence.TypedQuery - JPA Interface

The JPA Query API section (in chapter 4 of the ObjectDB manual) provides detailed explanation of how exactly to use these interfaces to build and run JPQL queries.

The TypedQueryjavax.persistence.TypedQuery - JPA InterfaceInterface used to control the execution of typed queries. interface (or alternatively the older Queryjavax.persistence.Query - JPA InterfaceInterface used to control query execution.javax.jdo.Query - JDO InterfaceThe Query interface allows applications to obtain persistent instances, values, and aggregate data from the data store. interface) is the only neccessary interface for defining and running string based JPQL queries (e.g. "SELECT c FROM Country").

Criteria Query API

Building dynamic queries with a structure that is known only at runtime (e.g. depending on which fields are filled by a user in a form) can be done by concatenating JPQL strings into a valid complete JPQL query. JPA 2 introduced the JPA Criteria Query API, as a cleaner alternative that enables building a dynamic query by using instances of special types, representing query elements. Running criteria queries, however, still requires a TypedQueryjavax.persistence.TypedQuery - JPA InterfaceInterface used to control the execution of typed queries. or a Queryjavax.persistence.Query - JPA InterfaceInterface used to control query execution.javax.jdo.Query - JDO InterfaceThe Query interface allows applications to obtain persistent instances, values, and aggregate data from the data store. instance.

Building a dynamic query using the criteria API is managed by the CriteriaQuery interface:

• javax.persistence.criteria.CriteriaQuery - JPA Interface

As noted above, eventually every criteria query is managed by an ordinary TypedQueryjavax.persistence.TypedQuery - JPA InterfaceInterface used to control the execution of typed queries. instance. The CriteriaQueryjavax.persistence.criteria.CriteriaQuery - JPA InterfaceThe CriteriaQuery interface defines functionality that is specific to top-level queries. instance merely represents the query during its building, and is equivalent to a JPQL query string (i.e. to a String instance containing JPQL).

An essential interface for using the criteria API is the CriteriaBuilder interface:

• javax.persistence.criteria.CriteriaBuilder - JPA Interface

A CriteriaBuilderjavax.persistence.criteria.CriteriaBuilder - JPA InterfaceUsed to construct criteria queries, compound selections, expressions, predicates, orderings. instance is the factory of criteria queries as well as of criteria query elements. It can be obtained either by the EntityManagerFactoryjavax.persistence.EntityManagerFactory - JPA InterfaceInterface used to interact with the entity manager factory for the persistence unit.'s getCriteriaBuilderEntityManagerFactory.getCriteriaBuilder() - JPA MethodReturn an instance of CriteriaBuilder for the creation of CriteriaQuery objects. method or by the EntityManagerjavax.persistence.EntityManager - JPA InterfaceInterface used to interact with the persistence context.'s getCriteriaBuilderEntityManager.getCriteriaBuilder() - JPA MethodReturn an instance of CriteriaBuilder for the creation of CriteriaQuery objects. method (both methods are equivalent).

Criteria Query Elements

Criteria query elements are organized in this reference into three groups.

SELECT and ORDER BY elements (including tuples):

• Criteria Query Selection and Results

FROM clause elements (representing range variables, join and fetch):

• Criteria Query From Elements

Other criteria query expressions (for all the query clauses):

• Criteria Query Expressions