JPA、刷新和实体管理器同步

Question

我正在使用 Java EE、Netbeans 和外观会话 bean 来实现 JPA 层 (eclipselink)。

例如，我有两张桌子：花园 (1) ---> 树 (n)。

（脚本A）现在，我执行这个sn-p：

Garden mGarden = new Garden();
.....
gardenFacade.create(garden)

（脚本 B）然后：

Tree oneTree = new Tree();
oneTree.setGarden(mGarden);
treeFacade.create(oneTree);

这样，实体Tree就正确添加到我的数据库中了，外键也对了。

（脚本 C）当我调用时：

Garden findGarden = gardenFacade.find(gardenId);
int count = findGarden.getTreeCollection().size();

我数过 = 0 !!! 如果我重新启动 glassfish 或重新加载我的应用程序并执行这些 sn-ps，我的计数 = 1。

所以，我认为这是持久性上下文同步的问题，因为如果我将脚本 B 更改为：

Tree oneTree = new Tree();
oneTree.setGarden(mGarden);
treeFacade.create(oneTree);

mGarden.getTreeCollection().add(oneTree);
gardenFacade.edit(mGarden);

一切正常！ 我该如何解决这个问题？

编辑：

create --> getEntityManager().persist(entity);
edit ----> getEntityManager().merge(entity);
find ----> getEntityManager().find(entityClass, id);

Answer 1

看起来所有这些调用都使用相同的休眠会话，并且由于您未能正确初始化集合的两侧，当然您在集合中没有得到任何东西：

Garden mGarden = new Garden(); // create a new Garden instance
session.persist(mGarden); // now this Garden instance is persistent. 
                          // Its state will be written to the database at the 
                          // next flush
Tree oneTree = new Tree(); // create a new Tree instance
oneTree.setGarden(mGarden); // set the garden of the tree. This is a basic, simple 
                            // Java method call. Nothing will magically add the tree
                            // to the garden collection of trees if you don't do 
                            // it explicitely
session.persist(oneTree); // now this Tree instance is persistent. 
                          // Its state will be written to the database at the 
                          // next flush. 
Garden findGarden = session.get(Garden.class, gardenId); 
    // returns the garden that has the specific ID. It's already in the session: 
    // you created and attached it to the session at the beginning. And you 
    // never added anything to its collection of trees