hibernate - How to use Criteria Queries in Spring Boot Data Jpa Application

Question

I have an application that uses Spring Boot Data jpa . So far i am using a repository like this

public interface StudentRepository extends CrudRepository<StudentEntity, Integer>{
    @Query(value = "" 
        + "SELECT s.studentname "
        + "FROM   studententity s, "
        + "       courseentity c "
        + "WHERE  s.courseid = c.courseid "
        + "       AND s.courseid IN (SELECT c.courseid "
        + "                          FROM   courseentity c "
        + "                          WHERE  c.coursename = ?1)")
    List<String> nameByCourse(String coursename);
}

How can i make use of Criteria Query that Hibernate provides for such cases in a Spring Boot Application

Answer 1

From the docs

To enrich a repository with custom functionality you first define an interface and an implementation for the custom functionality. Use the repository interface you provided to extend the custom interface.

Define an interface like so

public interface StudentRepositoryCustom {

    List<String> nameByCourse(String coursename);

}

Then define a custom implementation of this interface like so

@Service
class StudentRepositoryImpl implements StudentRepositoryCustom {

    @PersistenceContext

    private EntityManager em;

    public List<String> nameByCourse(String coursename) {            
        CriteriaBuilder cb = em.getCriteriaBuilder();
        //Using criteria builder you can build your criteria queries.
    }

}

Now you can extend this custom repository implementaion in your JPA repository like so.

public interface StudentRepository extends CrudRepository<StudentEntity, Integer>, StudentRepositoryCustom {

}

Learn more about criteria query and criteria builder here