onetomanytestsessionbean.java

有关EJB3的实体BEAN的一对多关系的实例

package OneToManySessionBean;

import javax.ejb.Stateless;
import OneToManyEntityBean.*;
import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.Query;

@Stateless
public class OneToManyTestSessionBean implements OneToManyTestSessionBeanRemote {

	@PersistenceContext
	protected EntityManager em;

	public void insertClasses() {
		Classes classes = new Classes();
		classes.setCollege("软件学院");
		classes.setSpecialty("软件工程");
		classes.setClassesName("0504班");
		classes.addStudent(new Student("李天翔"));
		classes.addStudent(new Student("李小胖"));
		em.persist(classes);
	}

	public Classes getClassesByID(Integer classesid) {
		Classes classes = em.find(Classes.class, classesid);
		classes.getStudents().size();
		// 因为是延迟加载，通过执行size()这种方式获取订单下的所有订单项
		return classes;
	}

	public List getAllClasses() {
		Query query = em
				.createQuery("select DISTINCT c from Classes c inner join fetch c.students order by c.classesid");
		List result = query.getResultList();
		return result;
	}
}