Post date: Mar 08, 2012 11:37:29 PM
Suppose there are entity classes
@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 HQL will be look like:
SELECT DISTINCT a FROM Author a INNER JOIN a.books b WHERE b.publisher.name = 'XYZ Press'
Another way to write java using HDL will be look like:
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();
}