Re: re[eclipselink-users] cursive parent-children relationship cached in

[James Sutherland <jamesssss@xxxxxxxxx>]

Nothing complex, just meant setting the children directly.  If you set the
ones from the shared cache (session), there is no dirty issue, just set them
up before registering them in a UnitOfWork / em.  If you want to set the
children in a UnitOfWork, if you are using change tracking (default in JPA),
you can set them through reflection, or set the variable directly, if using
deferred (default outside JPA) you would need to set the value in the clone
and the backup clone (which you can get from the uow.getBackupClone()).


Jason Kinzer wrote:
> 
> Thanks very much for the response James. This is probably a RTFM, but I'd
> really appreciate a pointer on where to start with that. Were you me would
> you consider a custom indirection container and an checking the onBuild
> (or
> whatever it is) event? Or does EclipseLink have some sort of 'custom
> populator' infrastructure I can tie into? Or am I making this too hard - I
> assumed doing the dumbest thing and setting the children doesn't really
> work
> well since it 'dirties' the object?
> 
> On Wed, Dec 17, 2008 at 3:12 PM, James Sutherland
> <jamesssss@xxxxxxxxx>wrote:
> 
>>
>> This is definitely not supported, and I'm not sure it would be possible,
>> as
>> you have to assume you have all of the children, which the where clause
>> may
>> filter out, and you also need to figure out which parent each child
>> belongs
>> to.  Perhaps #3.
>>
>> Using batch reading on the children relationship is probably the best
>> option, you will get n=depth selects, which should be close to optimal.
>>
>> If you really need the single select, you might try matching up the
>> children
>> in memory yourself, and setting the children directly.
>>
>>
>>
>> Jason Kinzer wrote:
>> >
>> > Hi,
>> >
>> > I have a  self-referential/recursive parent-children relationship (i.e.
>> > hierarchy) that I'm fumbling around with and would greatly appreciate
>> > suggestions.
>> >
>> > My naive attempt (snippet at the bottom) works merrily, but performance
>> is
>> > not all I'd hoped for. The entire hierarchy is guaranteed to get
>> > traversed,
>> > is very heavily used, and is read-only - so what I'd like to accomplish
>> is
>> > to eagerly read in the entire hierarchy in one fell swoop [to get it
>> fully
>> > cached]. I have tried to using batching on the 'children' collection or
>> > inner join on them and walking the hierarchy manually in code, but this
>> > generates far too many fetches - in principle only *one* fetch is
>> required
>> > here.
>> >
>> > Most fortunately I'm on Oracle and Eclipselink has connect-by support.
>> > This
>> > gets me *almost* exactly what I want (a single fetch). And there was
>> much
>> > rejoicing:
>> >
>> >                     ReadAllQuery hquery = new ReadAllQuery();
>> >                     ExpressionBuilder eb = new ExpressionBuilder();
>> >                     Expression startWith =
>> >
>> eb.get("id").equal(root.getId()).and(eb.get("sceId").equal(root.getSceId()));
>> >                     Expression connectBy = eb.get("children");
>> >                     Vector order = new Vector();
>> > order.addElement(eb.get("id"));
>> >                     hquery.setHierarchicalQueryClause(startWith,
>> > connectBy,
>> > order);
>> >                     hquery.setReferenceClass(Node.class);
>> >                     session.executeQuery(hquery);
>> >
>> > Unfortunately while this caches all the nodes, it does not cache the
>> > "children" collection. So, if my perform my "walk" over the hierarchy
>> it
>> > still fetches for each node to build the "children" collection. Much
>> > sadness.
>> >
>> > Now, with any other sort of query where the collection is not
>> > joined/batched, I can understand this: it can't t know who belongs in
>> the
>> > collection so even though the members are present it will have to build
>> it
>> > anyway.  However, in a connect-by query like this it *does* know the
>> > children.
>> >
>> > So basically, my feeling is that when I give it "Expression connectBy =
>> > eb.get("children")" this should be a hint to EclipseLink to go ahead
>> and
>> > populate the collection that denotes. So I'd like to know which one of
>> the
>> > following hold:
>> > 1. It should in fact populate the collection and I'm screwing something
>> up
>> > 2. There's some fundamentaly reason it can't correctly work the way I
>> want
>> > 3. This is a feature enhancement
>> >
> 
> 


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