JDO拥有的一对多子实体没有持久化

Question

我试图按照https://groups.google.com/forum/?fromgroups#!topic/google-appengine-java/KNnDuZ3yXkM中描述的方式，在GAE中使用JDO将子实体保持在双向一对多拥有的关系中，这表示新的孩子需要简单地添加到父对象的“子列表”成员作为事务的一部分。但是，我的子对象不会保留在数据存储区中。

我正在使用GWT 2.5.1，google appengine 1.8.0，主要在开发模式下尝试。

我的父类是UserData，子类是Category2。 以下是父类的相关部分：

@PersistenceCapable(identityType = IdentityType.APPLICATION, detachable = "true")
public class UserData implements IsSerializable {
    @NotPersistent
    public static final int CURRENT_EPOCH = 1;

    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Long key;

    @Persistent(mappedBy = "userData")
    @Order(extensions = @Extension(vendorName="datanucleus",
                key="list-ordering", value="category asc"))
    public List<Category2> categories;

    ...

    public UserData() {
        this.categories = new LinkedList<Category2>();
        ...
    }
}

和子类：

@PersistenceCapable(identityType = IdentityType.APPLICATION, detachable = "true")
public class Category2 implements IsSerializable {

    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    @Extension(vendorName="datanucleus", key="gae.encoded-pk", value="true")
    private String key;
    @Persistent
    private UserData userData;

    @Persistent
    private String category;
    @Persistent
    private String subcategory;
    @Persistent
    private boolean obsolete;

    public Category2() {
    }

    public Category2(String cat, String subcat, boolean obsolete) {
        this.category = cat;
        this.subcategory = subcat;
        this.obsolete = obsolete;
    }
    ...
}

我正在执行的代码是：

PersistenceManager pm = PMF.get().getPersistenceManager();

// Get the UserData object for this user
UserData userData;
Query q = pm.newQuery(UserData.class);
List<UserData> list = (List<UserData>) q.execute();
if (list.size() == 1) {
    userData = list.get(0);
} else {
    throw new BasileException("Found " + list.size() +
            " UserData objects");
}

Category2 cat = new Category2("MyCat", "MySubcat", false);
LOG.log(Level.INFO, "Adding category. Current num cats: " + 
        userData.categories.size());
Transaction tx = null;
tx = pm.currentTransaction();
try {
    tx.begin();
    q = pm.newQuery(Category2.class,
            "category == cat && subcategory == subcat");
    q.declareParameters("String cat, String subcat");
    List<Category2> cats = (List<Category2>) q.execute(
            cat.getCategory(), cat.getSubcategory());
    assert(cats.size() <= 1);
    if (cats.size() == 1)
        LOG.log(Level.INFO, "Category " + cat + " already exists!");
    else
        LOG.log(Level.INFO, "Category did not exist");

    userData.categories.add(cat);
    tx.commit();
    LOG.log(Level.INFO, "Num cats now: " + userData.categories.size());
} finally {
    if (tx.isActive()) {
        LOG.log(Level.INFO, "Transaction aborted!");
        tx.rollback();
    }
    pm.close();
}

每次运行代码时我得到的输出（在GWT devmode中）是：

[java] 05-Jun-2013 14:31:41 com.appspot.basileexp.server.BasileServiceImpl2 runRepro
[java] INFO: Adding category. Current num cats: 0
[java] 05-Jun-2013 14:31:42 com.appspot.basileexp.server.BasileServiceImpl2 runRepro
[java] INFO: Category did not exist
[java] 05-Jun-2013 14:31:42 com.appspot.basileexp.server.BasileServiceImpl2 runRepro
[java] INFO: Num cats now: 1

并在管理控制台中检查数据存储区显示数据存储区中没有Category2实体。

这是我的jdoconfig.xml以防万一：

<?xml version="1.0" encoding="utf-8"?>
    <jdoconfig xmlns="http://java.sun.com/xml/ns/jdo/jdoconfig"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:noNamespaceSchemaLocation="http://java.sun.com/xml/ns/jdo/jdoconfig">
      <persistence-manager-factory name="xg-transactions">
        <property name="javax.jdo.PersistenceManagerFactoryClass" value="org.datanucleus.store.appengine.jdo.DatastoreJDOPersistenceManagerFactory"/>
        <property name="javax.jdo.option.ConnectionURL" value="appengine"/>
        <property name="javax.jdo.option.NontransactionalRead" value="true"/>
        <property name="javax.jdo.option.NontransactionalWrite" value="true"/>
        <property name="javax.jdo.option.RetainValues" value="true"/>
        <property name="datanucleus.appengine.autoCreateDatastoreTxns" value="true"/>
      </persistence-manager-factory>
    </jdoconfig>

知道我在这里做错了吗？