Hibernate限制ManyToMany

Question

我有一个包含课程列表的Teacher课程，现在我不知道如何使用hibernate criteria和限制对这个课程列表进行过滤？

public class Teacher extends BaseEntity implements Serializable {
   @ManyToMany(targetEntity = Course.class, fetch = FetchType.EAGER)
   private Set<Course> courses;
}

public class TeacherSearchCriteria extends Criteria { 
    private Course course; 
}

这是我提供限制逻辑的服务类：

    EntityManager em = getEntityManager();
    CriteriaBuilder builder = em.getCriteriaBuilder();
    List<Teacher> result = Collections.EMPTY_LIST;

    CriteriaQuery<Teacher> criteria = builder.createQuery(Teacher.class);
    Root<Teacher> from = criteria.from(Teacher.class);

    if (searchCriteria != null) {
        List<Predicate> restrictions = new ArrayList<Predicate>();

        if (searchCriteria.getCourse() != null) {
            //Here I don't know how to make the restrictions on Set of 
            //courses
            restrictions.add(builder.equal(from.get("courses"), 
            searchCriteria.getCourse()));
        }
        addRestrictionsToCriteria(restrictions, criteria, builder);
    } 

Answer 1

您需要为您的收藏集创建alias。然后，您可以对集合中的属性添加限制。别名的创建告诉hibernate在构造sql时执行对表的连接。

EntityManager em = getEntityManager();
CriteriaBuilder builder = em.getCriteriaBuilder();
List<Teacher> result = Collections.EMPTY_LIST;

CriteriaQuery<Teacher> criteria = builder.createQuery(Teacher.class);
criteria.createAlias("courses", "c")
       .add(Restrictions.eq("c", searchCriteria.getCourse());