I don't have much idea.
I saved list in database and I was not able to read list back.
You can read solution to my problem at
http://groups.google.com/group/google-appengine-java/browse_thread/thread/2047db275a9014a4/20cabaf1b113963c#20cabaf1b113963c
You have IdentityType.APPLICATION,detachable = "true"
So I am not sure whether my reply would help you.
Regards
Sahil Mahajan
On Jan 14, 6:13 am, drdbuck <[email protected]> wrote:
> Max Ross said...
> ...Please post your question on the Google Group for GAE Java (the
> link is in the App Engine Links section on the right) along with your
> model objects and the code you're using to query for the child
> objects....
> ================================================================
>
> I have been attempting to do an owned one-to-many and have followed
> the example here. I have also tried for more than 10 hours
> experimenting with sight variations (looking at other examples) and
> using the debugger. I save the parent with a long list of children
> with no erros. No matter what I do it when I query and get the parent,
> the child list comes back empty. My datastore now has 10s of parent
> records.
>
> One difference is that my fields are public. Is that the problem?
> I don't think it could be.
>
> Another difference is that when I use:
> public List chapters = new ArrayList();
>
> When I try not using generics on the ArrayList I get the following
> runtime error:
> Jan 12, 2010 8:56:59 PM
> com.google.appengine.tools.development.ApiProxyLocalImpl log
> SEVERE: [1263329819732000] javax.servlet.ServletContext log:
> Exception while dispatching incoming RPC call
> com.google.gwt.user.server.rpc.UnexpectedException: Service method
> 'public abstract java.lang.String lt.client.GreetingService.greetServer
> (java.lang.String)' threw an unexpected exception:
> org.datanucleus.jdo.exceptions.ClassNotPersistenceCapableException:
> The class "The class "lt.server.Book" is not persistable. This means
> that it either hasnt been enhanced, or that the enhanced version of
> the file is not in the CLASSPATH (or is hidden by an unenhanced
> version), or the Meta-Data/annotations for the class are not found."
> is not persistable. This means that it either hasnt been enhanced, or
> that the enhanced version of the file is not in the CLASSPATH (or is
> hidden by an unenhanced version), or the Meta-Data for the class is
> not found.
>
> I don't get the ClassNotPersistenceCapableException runtime error if I
> declare the list as:
> public List⟨Chapter⟩ chapters = new ArrayList〈Chapter〉
> ();
> However, I am unable to query and get back any of the items that were
> in the list.
>
> I have also tried
> @Persistent (defaultFetchGroup = "true")
> private Book theBook;
> in the child, and that gets this warning:
> Jan 12, 2010 8:06:34 PM
> org.datanucleus.store.appengine.MetaDataValidator warn
> WARNING: Meta-data warning for lt.server.Lyric.theBook: The
> datastore does not support joins and therefore cannot honor requests
> to place child objects in the default fetch group. The field will be
> fetched lazily on first access. You can modify this warning by setting
> the datanucleus.appengine.ignorableMetaDataBehavior property in your
> config. A value of NONE will silence the warning. A value of ERROR
> will turn the warning into an exception.
>
> To clarify the above, I think I have tried everything except private
> fields and a non-generic ArrayList. I have never been able to get the
> child records back, although I get the parent.
>
> (I have edited the above to change from Song to Book and Lyric to
> Chapter to agree with your example)
>
> Here is my query code:
> public lt.client.Song getSong(String input) {
> lt.client.Song result = null;
> Song theSong = null;
> PersistenceManager pm = pmfInstance.getPersistenceManager();
> try {
> String query = "select from " + Song.class.getName()
> + " where name == lastNameParam "
> + " parameters String lastNameParam ";
> List<Song> songs = (List<Song>)
> pm.newQuery(query).execute(input);
> for (Song aSong : songs)
> theSong = aSong;
> List<lt.client.Lyric> ll = new
> ArrayList<lt.client.Lyric>();
> if (theSong != null) {
> if (theSong.lyrics != null)
> for (Lyric l :
> (List<Lyric>)theSong.lyrics) {
> ll.add(new
> lt.client.Lyric(l.measure, l.words));
> }
> if (ll.size() == 0) {
> List<String> emptyLyric = new
> ArrayList<String>();
> emptyLyric.add("emptyLyric");
> ll.add(new
> lt.client.Lyric("EmptyMeasure", emptyLyric));
> }
> result = new lt.client.Song(theSong.name, ll);
> }
> } finally {
> pm.close();
> }
> if (result != null)
> return result;
> return new lt.client.Song("Song not found",
> new ArrayList<lt.client.Lyric>());
> }
>
> }
>
> Here are my classes:
>
> package lt.server;
>
> import java.io.*;
> import java.util.*;
>
> import javax.jdo.annotations.*;
> import javax.jdo.*;
> import javax.persistence.Entity;
>
> import com.google.appengine.api.datastore.Key;
>
> @PersistenceCapable(identityType = IdentityType.APPLICATION,
> detachable = "true")
> public class Song implements Serializable {
> @SuppressWarnings("unused")
> @PrimaryKey
> @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
> private com.google.appengine.api.datastore.Key key;
>
> @Persistent
> public String name;
>
> @Persistent(mappedBy = "theSong")
> @Element(dependent = "true")
> //public List<Lyric> lyrics = new ArrayList<Lyric>();
> public List lyrics = new ArrayList();
>
> public void initSong(PersistenceManager pm, Reader input) {
> StreamTokenizer st = new StreamTokenizer(input);
> name = "";
> st.resetSyntax();
> st.wordChars('\u0021', '\u00FE');
> st.whitespaceChars('\u0000', '\u0020');
> st.eolIsSignificant(true);
> st.slashSlashComments(false);
> List<String> words = new ArrayList<String>();
> String measure = "";
> try {
> while (st.nextToken() != StreamTokenizer.TT_EOL
> && st.ttype !=
> StreamTokenizer.TT_EOF) {
> name += (st.sval + " ");
> }
> if (st.ttype != StreamTokenizer.TT_EOF) {
> while (st.nextToken() ==
> StreamTokenizer.TT_EOL)
> ;
> if (st.ttype != StreamTokenizer.TT_EOF) {
> if (st.sval.substring(0,
> 1).equals("|")) {
> if (st.sval.length() > 1)
> measure =
> st.sval.substring(1);
> else {
> while (st.nextToken()
> == StreamTokenizer.TT_EOL)
> ;
> if (st.ttype !=
> StreamTokenizer.TT_EOF) {
> measure =
> st.sval;
> }
> }
> } else {
> st.pushBack();
> measure = "";
> }
> if (st.ttype !=
> StreamTokenizer.TT_EOF) {
> boolean pendingLyric = false;
> while (st.nextToken() !=
> StreamTokenizer.TT_EOF) {
> if (st.ttype ==
> StreamTokenizer.TT_EOL) {
> pendingLyric
> = true;
> while
> (st.nextToken() == StreamTokenizer.TT_EOL)
> ;
> }
> if (st.ttype !=
> StreamTokenizer.TT_EOF) {
> if
> (st.sval.substring(0, 1).equals("|")) {
>
> pendingLyric = false;
>
> lyrics.add(new Lyric(pm, this, measure,
>
> words));
> words
> = new ArrayList<String>();
> if
> (st.sval.length() > 1)
>
> measure = st.sval.substring(1);
> else {
>
> while (st.nextToken() == StreamTokenizer.TT_EOL)
>
> ;
>
> if (st.ttype != StreamTokenizer.TT_EOF) {
>
> measure = st.sval;
>
> }
> }
> } else {
> if
> (pendingLyric) {
>
> pendingLyric = false;
>
> lyrics.add(new Lyric(pm, this, measure,
>
> words));
>
> words = new ArrayList<String>();
>
> measure = "";
> }
>
> words.add(st.sval);
> }
> }
> }
> }
> }
> }
> } catch (IOException ioe) {
> }
> if (words.size() > 0)
> lyrics.add(new Lyric(pm, this, measure, words));
> }
>
> }
>
> package lt.server;
>
> import java.io.Serializable;
> import java.util.*;
>
> import javax.jdo.annotations.*;
> import javax.jdo.*;
>
> @PersistenceCapable(identityType = IdentityType.APPLICATION,
> detachable = "true")
> public class Lyric implements Serializable {
> @SuppressWarnings("unused")
> @PrimaryKey
> @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
> private com.google.appengine.api.datastore.Key key;
>
> @SuppressWarnings("unused")
> //@Persistent (defaultFetchGroup = "true")
> @Persistent
> private Song theSong;
> @Persistent
> public List<String> words;
> @Persistent
> public String measure;
>
> public Lyric(PersistenceManager pm, Song theSong, String measure,
> List<String> words) {
> //pm.makePersistent(this);
> //this.theSong = theSong;
> this.measure = measure;
> this.words = words;
> //pm.makePersistent(this);
> }
>
> }
>
> The things that are commented out are left over from variations I have
> tried in the past. As I said I have done well over 10 hours of
> experimenting. I'm a professor of computer science and constantly
> find the errors in my students' code, but I can't seem to crack this
> one.--
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