使用 GAE/J DataNucleus 插件版本 2.1.2 无法获取新创建的 JDO 持久实体的 ID

Question

我的问题

我正在使用新的 1.7.5 GAE/J SDK 将我的应用程序从 1.x 版移植到 GAE/J 的 DataNucleus 插件 2.0 版。这将我的 JDO 版本从 2.3 更改为 3.0.1。我的持久实体类有一个编码字符串类型的主键，以及对对象数字 ID 的只读访问权限。每个实例都是其实体组的唯一成员（子级和父级仅通过数字 ID 链接）。

以前，我能够创建并持久化一个新的 MyEntity 实例，然后立即访问其数字 ID 以存储在父 MyEntity 实例的子 ID 列表中。

现在我发现新实例的数字 ID 在持久化后并不能立即使用——即使它是生成和存储的并且稍后可用。

我的问题

我可以做些什么来在对象创建和持久化后立即恢复对数字 ID 的访问？

“jdoconfig.xml”配置提取

<persistence-manager-factory name="big-table">
  <property
   name="javax.jdo.PersistenceManagerFactoryClass"
   value="org.datanucleus.api.jdo.JDOPersistenceManagerFactory"
  />
  <property name="datanucleus.DetachAllOnCommit" value="true"/>
  <property name="javax.jdo.option.NontransactionalRead" value="true"/>
  <property name="javax.jdo.option.NontransactionalWrite" value="true"/>
  <property
   name="datanucleus.appengine.autoCreateDatastoreTxns"
   value="true"
  />
  [...]
</persistence-manager-factory>

持久化实体类代码提取

@PersistenceCapable(identityType = IdentityType.APPLICATION, detachable = "true")
public class MyEntity implements Serializable
{
  private static final long serialVersionUID = 1L;

  // No setter for this read-only data member
  @PrimaryKey
  @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
  @Extension(vendorName="datanucleus", key="gae.encoded-pk", value="true")
  private String sEncodedKey;

  // No setter for this read-only data member
  @Persistent
  @Extension(vendorName="datanucleus", key="gae.pk-id", value="true")
  private Long loID;

  @Persistent
  private Long loParentID;

  //
  // Other persistent data members
  //

  public Long getID()
  {
    return loID;
  }

  //
  // Other getters and setters
  //
}

包含 3 个日志记录点的持久性代码

/**
 * Create a new entity.
 * @param loParentID
 *   The ID of the entity,
 *   a new child of which is to be created.
 * @param sChildName
 *   The name of the new child to be created.
 * @return
 *   The created entity child,
 *   or <code>null</code> if the operation was carried out unsuccessfully.
 */
public static MyEntity createEntityChild(Long loParentID, String sChildName)
{
  MyEntity meResult = null;
  MyEntity mePersistedChild = null;

  PersistenceManagerFactory pmf =
   DataExchange.getPersistenceManagerFactory();    // My own method
  PersistenceManager pm = pmf.getPersistenceManager();
  Transaction tx = pm.currentTransaction();
  try
  {
    tx.begin();

    MyEntity meChild = new MyEntity();
    meChild.setParentID(loParentID);
    meChild.setName(sChildName);
    meChild.setActive(true);
    mePersistedChild = pm.makePersistent(meChild);

    // "Touch" data member not in the default fetch group
    ArrayList<Long> liChildIDs = mePersistedChild.getChildIDs();
    if (liChildIDs != null)
      liChildIDs.size();

    if (mePersistedChild != null)
      g_logger.log(Level.FINE, String.format(
       "Pre-commit: mePersistedChild.getID() = %d,"
       + " mePersistedChild.getEncodedKey() = \"%s\".",
       mePersistedChild.getID(), mePersistedChild.getEncodedKey()));

    tx.commit();

    if (mePersistedChild != null)
      g_logger.log(Level.FINE, String.format(
       "Post-commit: mePersistedChild.getID() = %d,"
       + " mePersistedChild.getEncodedKey() = \"%s\".",
       mePersistedChild.getID(), mePersistedChild.getEncodedKey()));
  }
  finally
  {
    try
    {
      if (tx.isActive())    // Because of an exception, say
        tx.rollback();
    }
    finally
    {
      pm.close();
    }
  }

  if (mePersistedChild != null)
    g_logger.log(Level.FINE, String.format(
     "Post-pm-close: mePersistedChild.getID() = %d,"
     + " mePersistedChild.getEncodedKey() = \"%s\".",
     mePersistedChild.getID(), mePersistedChild.getEncodedKey()));

  [...]

  return meResult;
}

开发服务器日志输出

24-Feb-2013 13:28:02 [...].MyEntityBusiness createMyEntityChild
FINE: Pre-commit: mePersistedChild.getID() = null, mePersistedChild.getEncodedKey() = "agttYXJrZXQtdHJlZXISCxIMSXRlbUNhdGVnb3J5GAUM".

24-Feb-2013 13:28:03 [...].MyEntityBusiness createMyEntityChild
FINE: Post-commit: mePersistedChild.getID() = null, mePersistedChild.getEncodedKey() = "agttYXJrZXQtdHJlZXISCxIMSXRlbUNhdGVnb3J5GAUM".

24-Feb-2013 13:28:03 [...].MyEntityBusiness createMyEntityChild
FINE: Post-pm-close: mePersistedChild.getID() = null, mePersistedChild.getEncodedKey() = "agttYXJrZXQtdHJlZXISCxIMSXRlbUNhdGVnb3J5GAUM".

24-Feb-2013 13:28:07 com.google.appengine.api.datastore.dev.LocalDatastoreService$PersistDatastore persist
INFO: Time to persist datastore: 141 ms

JDO 增强版本验证

构建过程成功，输出片段：

datanucleusenhancer:
09:33:00,531 (main) INFO  [DataNucleus.Enhancer] - DataNucleus Enhancer for API "JDO"
09:33:01,125 (main) INFO  [DataNucleus.Enhancer] - DataNucleus Enhancer (version 3.1.1) : Enhancement of classes
DataNucleus Enhancer (version 3.1.1) : Enhancement of classes
09:33:03,281 (main) INFO  [DataNucleus.Enhancer] - Writing class file "[Path]\MyEntity.class" with enhanced definition
[... (N entries in all)]
09:33:04,046 (main) INFO  [DataNucleus.Enhancer] - DataNucleus Enhancer completed with success for [N] classes. Timings : input=1922 ms, enhance=984 ms, total=2906 ms. Consult the log for full details
DataNucleus Enhancer completed with success for [N] classes. Timings : input=1922 ms, enhance=984 ms, total=2906 ms. Consult the log for full details

软件环境

• Web 服务器：Google App Engine for Java 1.7.5 版
• Web 框架：Apache Wicket 6.5.0
• Java 版本：1.6.0_39； Java HotSpot(TM) 客户端虚拟机 20.14-b01
• GAE/J DataNucleus 插件版本：2.1.2
• DataNucleus 访问平台版本：3.1.3
• JDO 版本：3.0.1
• 操作系统：在 x86 上运行的 Microsoft Windows XP 5.1 版
• IDE：NetBeans 7.2（内部版本 201207171143）

Answer 1

GAE JDO 插件仅在从数据存储区读取标有该字段的字段时设置“gae.pk-id”/“gae.pk-name”字段（只需在 SVN 主干中进行搜索，FetchFieldManager 是加载它的唯一位置 - 它在执行 PUT 时不会设置它）。不知道它在 1.x 中做了什么，但 GAE 自己的所有测试在 2.x 中都通过了，就像在 1.x 中一样。但是那个“特性”无论如何都不是标准的 JDO，所以我对它没什么兴趣。

JDO 提供lifecycle listener，您可以轻松设置 postStore 回调并在其中设置对象中的某些字段（并且不依赖于 AppEngine 特定的“功能”）。

Answer 2

受到@DataNucleus 的 cmets 的启发，我以一种类似的精神进行了解决。下面列出的解决方法对我有用，但我发现我的根本问题仍然存在。

使用编码键字符串的（只读）数字 ID 的所有持久实体都需要更改其 getID() 方法才能使用解决方法。

Java 代码

我将我的 ID getter 方法（前面给出）修改如下：

public Long getID()
{
  Long loResult = DataExchange.getIDFromEKSIfIDIsNull(loID, sEncodedKey);
  return loResult;
}

我的DataExchange 类有新方法：

import com.google.appengine.api.datastore.Key;
import com.google.appengine.api.datastore.KeyFactory;

/**
 * Get the ID supplied, or get it from the encoded key string if the ID is
 * <code>null</code>.
 * <br/>
 * This method is necessary since JDO version 3.0.1 introduces a long delay
 * between entity first persistence and ID availability using the DataNucleus
 * GAE primary key ID plug-in.
 * @param loID
 *   The persistent entity ID.
 *   This may be <code>null</code> if the entity has been persisted for the
 *   first time but its generation is delayed (a big hello to JDO version
 *   3.0.1).
 * @param sEncodedKey
 *   The persistent entity encoded key string.
 *   This should be not <code>null</code> if the entity has been persisted.
 * @return
 *   <ul>
 *     <li>
 *       If the persistent entity ID supplied is not <code>null</code>
 *       then return it
 *     </li>
 *     <li>
 *       else if the encoded key string is not <code>null</code> then extract
 *       the ID and return it
 *     </li>
 *     <li>
 *       else return <code>null</code>.
 *     </li>
 *   </ul>
 */
public static Long getIDFromEKSIfIDIsNull(Long loID, String sEncodedKey)
{
  Long loResult = null;

  if (loID != null)
    loResult = loID;
  else if (sEncodedKey != null)
  {
    Key key = KeyFactory.stringToKey(sEncodedKey);
    if (key != null)
    {
      long loIDFromEKS = key.getId();
      loResult = Long.valueOf(loIDFromEKS);
    }
  }

  return loResult;
}