Question

我正在使用Java EE，Netbeans和Facade会话bean来实现JPA层（eclipselink）。

我有一张两张桌子例如：Garden（1）---＆gt;树（n）。

（脚本A）现在，我执行这个片段：

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

（剧本B）然后：

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

通过这种方式，实体树被正确添加到我的数据库中，外键是正确的。

（脚本C）当我调用时：

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

我算了= 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片段，我会计算= 1。

所以，我认为这是持久性上下文同步的问题，因为如果我改变我的脚本B：

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hibernate会话，并且你无法正确初始化集合的两面，当然你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

JPA，flush和Entity Manager同步

1 个答案: