复制实体集合并坚持在Hibernate / JPA中(Duplicate a collection of entities and persist in Hibernate/JPA)

 我想要复制数据库中的实体集合。 我通过以下方式检索收藏： 
 
CategoryHistory chNew = new CategoryHistory();
CategoryHistory chLast =  (CategoryHistory)em.createQuery("SELECT ch from CategoryHistory ch WHERE ch.date = MAX(date)").getSingleResult;
List<Category> categories = chLast.getCategories();
chNew.addCategories(categories)// Should be a copy of the categories: OneToMany
 
 现在我想复制'类别'的列表并将其与EntityManager一起保存。 我正在使用JPA / Hibernate。 UPDATE 
 
 知道如何分离我的实体后，我需要知道要分离的内容：当前代码： 
 
    CategoryHistory chLast =  (CategoryHistory)em.createQuery("SELECT ch from CategoryHistory ch WHERE ch.date=(SELECT MAX(date) from CategoryHistory)").getSingleResult();
    Set<Category> categories =chLast.getCategories();

    //detach
    org.hibernate.Session session = ((org.hibernate.ejb.EntityManagerImpl) em.getDelegate()).getSession();
    session.evict(chLast);//detaches also its child-entities?       

    //set the realations
    chNew.setCategories(categories);
    for (Category category : categories) {
        category.setCategoryHistory(chNew);
    }
    //set now create date
    chNew.setDate(Calendar.getInstance().getTime());

    //persist
    em.persist(chNew);
 
 这会抛出一个failed to lazily initialize a collection of role: entities.CategoryHistory.categories, no session or session was closed异常。 
 
 我认为他想要再次加载类别，因为我让它们分离。 我现在应该怎么做？ 

I want to duplicate a collection of entities in my database. I retreive the collection with:
 
CategoryHistory chNew = new CategoryHistory();
CategoryHistory chLast =  (CategoryHistory)em.createQuery("SELECT ch from CategoryHistory ch WHERE ch.date = MAX(date)").getSingleResult;
List<Category> categories = chLast.getCategories();
chNew.addCategories(categories)// Should be a copy of the categories: OneToMany
 
Now i want to duplicate a list of 'categories' and persist it with EntityManager. I'm using JPA/Hibernate. UPDATE
 
After knowing how to detach my entities, i need to know what to detach: current code:
 
    CategoryHistory chLast =  (CategoryHistory)em.createQuery("SELECT ch from CategoryHistory ch WHERE ch.date=(SELECT MAX(date) from CategoryHistory)").getSingleResult();
    Set<Category> categories =chLast.getCategories();

    //detach
    org.hibernate.Session session = ((org.hibernate.ejb.EntityManagerImpl) em.getDelegate()).getSession();
    session.evict(chLast);//detaches also its child-entities?       

    //set the realations
    chNew.setCategories(categories);
    for (Category category : categories) {
        category.setCategoryHistory(chNew);
    }
    //set now create date
    chNew.setDate(Calendar.getInstance().getTime());

    //persist
    em.persist(chNew);
 
This throws a failed to lazily initialize a collection of role: entities.CategoryHistory.categories, no session or session was closed exception.
 
I think he wants to lazy load the categories again, as i have them detached. What should i do now?

原文：https://stackoverflow.com/questions/1973877