Max is right, although there's a small issue with the syntax:
@Persistent(mappedBy="parent", defaultFetchGroup = "true")
public List<Child> childs;
- Jason
On Mon, Oct 19, 2009 at 10:26 PM, Max Zhu <thebb...@gmail.com> wrote:
> 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 <lsor...@gmail.com> 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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