[英]Hibernate (JPA) how to do an eager query, loading all child objects
[英]How do I use eager Instantiation in Hibernate?
<!-- Clasa Proiect-->
<class catalog="tema3" name="com.tema3.tables.Proiect" table="proiect" lazy="false">
<id column="proiect_id" name="id">
<generator class="native"/>
</id>
<property name="nume" type="text" />
<set name="itemList" table="proiect_item" fetch="select">
<key column="proiect_id"/>
<many-to-many column="item_id" unique="true" class="com.tema3.tables.Item"/>
</set>
</class> </class>
那是我的映射 class。
我稱之為實例化的代碼是:
Session session = HibernateUtil.getSessionFactory().getCurrentSession();
session.beginTransaction();
Query q = session.createQuery("from Proiect");
List<Proiect> lists = HibernateUtil.listAndCast(q);
session.getTransaction().commit();
obj = lists;
這是listandCastMethod:
public static <T> List<T> listAndCast(Query q) {
@SuppressWarnings("unchecked")
List list = q.list();
return list;
}
我不斷得到一個:
May 2, 2011 4:38:03 PM org.hibernate.LazyInitializationException <init>
SEVERE: failed to lazily initialize a collection of role: com.tema3.tables.Proiect.itemList, no session or session was closed
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.tema3.tables.Proiect.itemList, no session or session was closed
at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:358)
但問題是 Proiet class 的字段已填充,但我得到此異常的項目集除外,但我希望填充項目集。我該怎么做?
在返回或調用transaction.commit()
之前初始化listAndCast(Query q)
方法中的項目集。 這可以通過調用項目集中的元素上的任何訪問器來完成。 這將強制 hibernate 初始化項目集,而不是返回代理列表。
編輯
Session session = HibernateUtil.getSessionFactory().getCurrentSession();
session.beginTransaction();
Query q = session.createQuery("from Proiect");
List<Project> lists = HibernateUtil.listAndCast(q);
if(lists != null && lists.size() > 0) {
Set<Item> s = lists.get(0).getItemList();
Iterator iter = s.iterator();
while(iter.hasNext()) {
Item item = iter.next();
item.getSomething();
break;
}
}
session.getTransaction().commit();
obj = lists;
我找到了答案。它需要在 XML 的集合聲明中添加屬性lazy="false"
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