JPQL Eager Fetch Plan Configuration Question

krawling · **Posted:** Thu Jan 25, 2007 7:28 pm

Hello All,

I am currently evaluating ORM solutions, including Hibernate 3.2 and KODO 4.1 running in Glassfish v1.

I have the following scenario where I have 2 entities with a lazy one-to-one bi-directional relationship : AC <-- AP

I have written a query to return a list of AC objects and want to fetch the related AP objects as well :

@NamedQuery(name="AC.findACListByValueWithFetchJoin3",
query="SELECT DISTINCT c FROM AC c JOIN FETCH
c.ap " + "WHERE c.value = :value")

Hibernate will fetch in a list of all of the AC and AP objects and totally resolve both ends of the relationship; however, if will run n+1 queries. It appears that the n queries are to resolve the inverse side of the relationship.

In the corresponding Kodo test, it will eventually execute the n+1 but only when the inverse relationship is accessed.

Is it possible in Hibernate to setup a fetching strategy to load all of the objects but lazily resolve the inverse relationships?

Thanks for the time.

Regards,
Kurt

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

Are you remembering to put the constrained="true" attribute in your inverse one-to-one element? If you skip it, then the relationship cannot be proxied, and the original objects will be eagerly loaded. If you loaded the objects first, then inflated the associated objects, you wouldn't see the n queries, because they'd all be in the session cache already.

krawling · **Posted:** Fri Jan 26, 2007 9:30 am

Thanks for the reply!

I am using annotations but I think the following definition of the inverse relationship would be equivalent to specifying constrained="true" in the xml :

Code:

// AC inverse relationship
@OneToOne(mappedBy="ap", optional=false, fetch=FetchType.LAZY)
private AC ac;

It appears that all the eagerly fetched objects are inflated with the exception of the inverse relationship which is proxied and then resolved with n queries.

Regards,
Kurt

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

I can't see anything in the annotations documentation that corresponds to the constrained="true" attribute. You many be out of luck. I'd experiment with many-to-one for the inverse association, but I can't see the equivalent of unique="true" in annoations.

krawling · **Posted:** Sat Feb 03, 2007 3:27 pm

Hello,

I did experiment with the @OneToMany on the inverse side and it looks like that may be a workaround for my scenario. I can eager fetch the entities on both sides of the relationship and the inverse association is fetched after on demand.

Thanks again for the replies.

Regards,
Kurt