Hello @,

we have db bottleneck after migration from Hibernate to JPA (3.2.5.ga
and Jboss 4.0.5 GA)

Scenario:



When Order instance is loaded using em.find than 2 select's are executed:

select * from Order
select * from Address where id = ? // order.addressid

The same is done when I have query which returns X orders (select on Adrress table is executed only one per address instance, e.g. order1 and order2 references same addressA object than only one select is executed to retrieve the addressA)

The same behaviour is in bidirectional scenario.

In original pure hibernate code join is executed immediately. The order's hbm file contains

<many-to-one
name="address"
column="addressId"
class="Address"
cascade="all"
unique="false"/>

I tried also to use hibernate specific @Fetch(SELECT) - without success

I would also like to avoid db schema change unless really neccesary

Thanks for any hint

Hi,

have you tried @Fetch(JOIN)? That should use a SQL join to load the data. However, I would have expected this to be the default.

--Hardy

Hello,

also tried JOIN. Without success.

Thx

Hello,

I realized that

em.find(Order.class, id)

will execute select where ORDER and ADDRESS tables are joined.

So it does not work for query like (given the val field is defined for order and there is exactly one instance with value val = val ==> no Exception thrown):



Only in this case correct order/address is retrieved but 2 statements are executed in database.

In case you have lot of records in database this is not very nice solution.

I have also tried "select o from Order join o.address where o.val = :val"

Thanks

Ok - finally fetch join solved the problem