Hi Lars,
Try to annotate your relationship as follows:
@Persistent(mappedBy="parent", default-fetch-group="true")
public List<Child> childs;
On Tue, Oct 20, 2009 at 12:19 AM, Lars <[email protected]> wrote:
>
> Hi,
> I am failing to retrieve child-objects in a one-to-many JDO relation
> in the datastore. The case is as follows;
>
> I have two classes (Parent & Child, code-snippet below) with a defined
> one-to-many relation.
> It is no problem storing the structure with the 'store'-operation
> defined below. This is easily verified by web-browsing the datastore.
>
> However, when retrievning the parent-object from the datastore
> ('fetchParents'), the ''childs' attribute is always null. What must be
> done to (auto-)populate this attribute from the datastore?
> Also, the 'parent'-attribute of the Child-objects will also be null if
> they are fetched in a similar way.
>
> All clues appreciated...
>
> Lars
>
> - - - - - - - Code samples below - - - - - -
>
> @PersistenceCapable(identityType = IdentityType.APPLICATION)
> public class ParentDTO {
> @PrimaryKey
> @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
> @Extension(vendorName="datanucleus", key="gae.encoded-pk",
> value="true")
> private String encodedKey;
>
> @Persistent
> public String name;
>
> @Persistent(mappedBy="parent")
> public List<Child> childs;
>
> public ParentDTO()
> {
>
> }
>
> public void add(Child c)
> {
> if (childs == null)
> childs = new ArrayList<Child>();
> kids.add(c);
> }
> }
>
> - - - -
>
> @PersistenceCapable(identityType = IdentityType.APPLICATION)
> public class Child {
> @PrimaryKey
> @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
> @Extension(vendorName="datanucleus", key="gae.encoded-pk",
> value="true")
> public String encodedKey;
> @Persistent
> public String name;
>
> @Persistent
> public Parent parent;
>
> public Child()
> {
> }
>
> public String getEncodedKey() {
> return encodedKey;
> }
> }
>
> - - - - -
>
> Storing to datastore (works perfectly)
>
> public void store()
> {
> Parent p = new Parent();
> p.navn = "nils";
>
> Child c = new Child();
> c.name = "jim";
> p.add(c);
>
> c = new ChildDTO();
> c.name = "anne";
> p.add(c);
>
> PersistenceManager pm =
> PMF.get().getPersistenceManager();
> try {
> pm.makePersistent(p);
> } catch (Exception ee) {
> res = ee.getMessage();
> } finally {
> pm.close();
> }
> }
>
> - - - - - - Fetching data (not working)
>
> public String fetchParents()
> {
> String res = "";
> PersistenceManager pm =
> PMF.get().getPersistenceManager();
>
> javax.jdo.Query query = pm.newQuery(Parent.class);
> List<Parent> parents = (List<Parent>) query.execute();
> Iterator<Parent> iterF = parents.iterator();
> while (iterF.hasNext()) {
> Parent f = iterF.next();
> res = res + ":" + f.name;
> if (f.childs != null) { // this is the
> problem - 'this.childs' is
> always null
> Iterator<Child> iterI =
> f.childs.iterator();
> while (iterI.hasNext()) {
> Child idto = iterI.next();
> res = res + ">" + idto.name
> ;
> }
> }
> }
> pm.close();
> }
>
> >
>
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