当使用@ElementCollection时,加载全部正在加载对象的多个实例.更具体地说,它正在为collectionOfStrings中的每个元素加载一个实例.
例如,具有单个实例MyClass的数据库与collectOfStrings.size()== 4,调用加载所有MyClass值将返回一个大小为4的列表(所有相同的对象),而不是只有1个对象.
// Parent class is a @MappedSuperclass which may or may not be relevant to the issue
@Entity
public class MyClass extends ParentClass {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private long id;
@ElementCollection(fetch=FetchType.EAGER)
@IndexColumn(name="indexColumn")
private List<String> collectionOfStrings;
// other instance variables,constructors,getters,setters,toString,hashcode and equals
}
public class MyClassDAO_Hibernate extends GenericHibernateDAO<MyClass,Long> implements MyClassDAO {
@Override
public List<MyClass> loadAll() {
List<MyClass> entityList = null;
Session session = getSession();
Transaction trans = session.beginTransaction();
entityList = findByCriteria(session);
trans.commit();
return entityList;
}
}
protected List<T> findByCriteria(Session session,Criterion... criterion) {
Criteria crit = session.createCriteria(getPersistentClass());
for (Criterion c : criterion) {
crit.add(c);
}
return crit.list();
}
MyClassDAO myClassDAO = new MyClassDAO_Hibernate(); // in reality,implementation type is determined with a Factory
...
List<MyClass> myClassInstances = myClassDAO.loadAll();
谢谢,
HeavyE
解决方法
我不知道这是否是一个错误或合法的行为,但可以通过应用DISTINCT_ROOT_ENTITY结果变量来修复：
protected List<T> findByCriteria(Session session,Criterion... criterion) {
Criteria crit = session.createCriteria(getPersistentClass());
for (Criterion c : criterion) {
crit.add(c);
}
crit.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);
return crit.list();
}
