IMHO auto-retrieve should be set to true only for table's reference (and not
in every cases). So by default my preconisation is to set auto-retrieve to
true in particulars cases well identified...
For the prefetched relationships as far as I know there is some restrictions
:
- only works if your objects are in the cache.
- it's not possible to retrieve instances farther than the first "layer" :
for example to stay with the model I introduce in my previous post I can't
directly prefetch listeC (a collection of C objects) from an instance of A.
I need to do this :
A result = (A)broker.getObjectByQuery(query);
broker.retrieveReference(result.getB(), "listeA");
broker.retrieveReference(result.getB(), "listeC");
And if I want to retrieve de D instance available on each C object I need
the to add the following code :
while (iter.hasNext()) {
C c = (C)iter.next();
broker.retrieveReference(c, "d");
}
I have the feeling that the use of the DeepRetrieve utility make the graph
object retrieving easier ...
Thanx for your feedback :-)
JB
-----Message d'origine-----
De: Jakob Braeuchi
A: OJB Users List
Date: 29/11/2004 18:48
Objet: Re: Deep retrieve : a proposal
hi jean-baptiste,
ojb already offers auto-retrieve = true in the collection-descriptor to
load
related objects automatically. an additional feature are the prefetched
relationships that allow you to load related object in a single query
instead of
executing one query for each parent object.
what is the additional benefit of DeepRetrieve ?
jakob
CLARAMONTE Jean-Baptiste schrieb:
> I've noticed that OJB doesn't offer a deep retrieve reference service,
so I
> have developped an utility for retrieving from one reference all the
deep
> references (and back references).
> Example :
> we have the following model :
> [A]<(*)listeA-----(1)b>[B]<(1)b-----(*)listeC>[C]-----(1)d>[D]
> /\
> (*)listeB
> ||
> (*)listeE
> \/
> [E]
>
> Supposing we already have retrieved a reference on [A] and now we
would like
> to retrieve all the references associated from this instance. Using
the
> DeepRerieve utility the following code will do the job for you :
>
> Criteria crit = new Criteria();
> crit.addEqualTo("idA", new Long(0));
>
> QueryByCriteria query = QueryFactory.newQuery(A.class, crit);
>
> A result = (A)broker.getObjectByQuery(query);
>
> DeepRetrieve deepRetrieve = new DeepRetrieve(broker);
> deepRetrieve.addRetrieveRef("b(listeA).listeC(b).d");
> deepRetrieve.addRetrieveRef("b.listeE(listeB)");
> deepRetrieve.retrieve(result);
>
> Without the DeepRetrieve utility the following code should have been
used :
>
> Criteria crit = new Criteria();
> crit.addEqualTo("idA", new Long(0));
>
> QueryByCriteria query = QueryFactory.newQuery(A.class, crit);
> query.addPrefetchedRelationship("b");
>
> A result = (A)broker.getObjectByQuery(query);
>
> broker.retrieveReference(result.getB(), "listeA");
> broker.retrieveReference(result.getB(), "listeC");
> Iterator iter = result.getB().getListeC().iterator();
> while (iter.hasNext()) {
> C c = (C)iter.next();
> broker.retrieveReference(c, "d");
> broker.retrieveReference(c, "b");
> }
>
> broker.retrieveReference(result.getB(), "listeE");
> iter = result.getB().getListeE().iterator();
> while (iter.hasNext()) {
> E e = (E)iter.next();
> broker.retrieveReference(e, "listeB");
> }
>
>
>>From my first tests this DeepRetrive leads to the same amount of sql
query.
> The code is easier to read. (well from my point of view...)
>
> regards,
>
> JB
>
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