When retrieving entity, hibernate first selects all primitive fields and ids for non-primitive fields in a select statement, then starting to select non-primitive fields using other statements. The problem is, if Class A has 100 non-primitive fields, then they will at least 100 statements used for only retriving a single A instance. Is there any way to optimize it to few selects?

I know fetch strategies could be configured, but after reading related document, still cannot figure out how to optimize it.

Thanks

The most important thing is to make sure that proxies are enabled for all classes. This is done on a class-by-class basis with <class ... lazy="true">.

If you want to override this for some associations you can specify <many-to-one ... fetch="join">. Hibernate will use a single query with join statements to also load the associated objects.

You may also consider using the second-level cache.

A lot of information about this can be found in the Hibernate documentation: http://www.hibernate.org/hib_docs/v3/re ... rmance.htm

It is kind of hard to answer questions about optimization without knowing anything about the data model, use cases, etc. Optimizing one use case may turn out to be very bad for something else. It is very often a matter of trying to find an acceptable average performance.

I've configured second-level cache. But it always miss hiting. Everytime I find the same entity, HB always logs the following log. I guess that means the entity is not loaded from cache.

2008-08-26 15:18:36,859 INFO [STDOUT] Hibernate: /* select m from Medium m */ select medium0_.medium_id as medium1_16_, medium0_.medium_desc as medium2_16_ from medium_lu medium0_

...

2008-08-26 15:18:40,375 DEBUG [org.hibernate.engine.TwoPhaseLoad] adding entity to second-level cache: [com.my.Medium#8]
2008-08-26 15:18:40,375 DEBUG [org.hibernate.cache.ReadOnlyCache] Caching: com.my.Medium#8
2008-08-26 15:18:40,375 DEBUG [org.hibernate.engine.TwoPhaseLoad] done materializing entity [com.my.Medium#8]

look down

how do you retrieve your entity? hql? try "left join fetch" then.

for example, if your class a has class b and class c, you could fetch all data at once by querying

from class a left join fetch a.b left join fetch a.c