JDO 1：N问题（检索数据）

Question

我上课要学习PDF

@PersistenceCapable
public class GoogleDrivePDF {

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

        @Persistent
        private String pdfName;

       ... geter, seter...

}

为了写入和读取数据，我喜欢这样：

GoogleDrivePDF pdf = new GoogleDrivePDF();
 key=KeyFactory.createKey(GoogleDrivePDF.class.getSimpleName(),"0B1IQEoiXFg3IWHhJNEtlMzlvQWs");
 pdf.setKey(key);           
 pdf.setPdfName("NAME");
 pm.makePersistent(pdf); 

并且为了阅读：

 pdf  = pm.getObjectById(GoogleDrivePDF.class,  "0B1IQEoiXFg3IWHhJNEtlMzlvQWs1");

一切正常！

现在我将创建 One：Many realationship。

    @PersistenceCapable
    public class UsersPDFDocuments {

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

        @Persistent
        private List<GoogleDrivePDF> pdfs;

        ... seter, geter...
}

我写信给数据库：

         List <GoogleDrivePDF> pdfFilesDao=...
         GoogleDrivePDF pdf = new GoogleDrivePDF();
         Key key= KeyFactory.createKey(GoogleDrivePDF.class.getSimpleName(), "0B1IQEoiXFg3IWHhJNEtlMzlvQWs1");
         pdf.setKey(key);
         pdf.setVerifyed(false);
         pdf.setPdfName("mari123");
         pdfFilesDao.add(pdf);  

         key= KeyFactory.createKey(UsersPDFDocuments.class.getSimpleName(), "mail@mail");
         UsersPDFDocuments userData = new UsersPDFDocuments();
         userData.setKey(key);
         userData.setPdfs(pdfFilesDao);

         pm.makePersistent(userData); 

确定一切正常！ 但我现在无法阅读PDF数据

我有错误：

HTTP ERROR 500

Problem accessing /test. Reason:


     Could not retrieve entity of kind GoogleDrivePDF with key GoogleDrivePDF("0B1IQEoiXFg3IWHhJNEtlMzlvQWs1")
    Caused by:

    javax.jdo.JDOObjectNotFoundException: Could not retrieve entity of kind GoogleDrivePDF with key GoogleDrivePDF("0B1IQEoiXFg3IWHhJNEtlMzlvQWs1")

但我做同样的事，就像我做的那样：

 Key key = KeyFactory.createKey(GoogleDrivePDF.class.getSimpleName(), "0B1IQEoiXFg3IWHhJNEtlMzlvQWs1");
         GoogleDrivePDF pdf = pm.getObjectById(GoogleDrivePDF.class,    key);

当我测试时，为了得到这个值，我需要一个enycrypted String of key。 （见图）agtsdHYtY2hlY2tlcnJoCxIRVXNlcnNQREZEb2N1bWVudHMiIXZha2h0YW5nLmtvcm9naGxpc2h2aWxpQGdtYWlsLmNvbQwLEg5Hb29nbGVEcml2ZVBERiIcMEIxSVFFb2lYRmczSVdIaEpORXRsTXpsdlFXcww

当我添加Unowned时，它有效！为什么？！

@Unowned
    @Persistent
    private List<GoogleDrivePDF> pdfs;