JPA Queries
Queries are represented in JPA by the Query and TypedQuery interfaces:
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 TypedQueryjakarta.persistence.TypedQueryInterface used to control the execution of typed queries. interface (or alternatively the older Queryjakarta.persistence.QueryInterface used to control query execution. 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 TypedQueryjakarta.persistence.TypedQueryInterface used to control the execution of typed queries. or a Queryjakarta.persistence.QueryInterface used to control query execution. instance.
Building a dynamic query using the criteria API is managed by the CriteriaQuery interface:
As noted above, eventually every criteria query is managed by an ordinary TypedQueryjakarta.persistence.TypedQueryInterface used to control the execution of typed queries. instance. The CriteriaQueryjakarta.persistence.criteria.CriteriaQueryThe 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:
A CriteriaBuilderjakarta.persistence.criteria.CriteriaBuilderUsed 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 EntityManagerFactoryjakarta.persistence.EntityManagerFactoryInterface used to interact with the persistence unit, and to create new instances of EntityManager.'s getCriteriaBuilderjakarta.persistence.EntityManagerFactory.getCriteriaBuilder()Return an instance of CriteriaBuilder which may be used to construct CriteriaQuery<T> objects. method or by the EntityManagerjakarta.persistence.EntityManagerInterface used to interact with the persistence context.'s getCriteriaBuilderjakarta.persistence.EntityManager.getCriteriaBuilder()Obtain an instance of CriteriaBuilder which may be used to construct CriteriaQuery<T> 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):
FROM clause elements (representing range variables, join and fetch):
Other criteria query expressions (for all the query clauses):