Hi,

we are developing an application with a quite complex object graph. An extract of our domain model looks like this:

Organsiation --1 ------- 1 -- User
Organisation --1 ------- n -- OrganisationalUnit
Organisation --1 ------- 1 -- OrganisationalUnit (root unit)
Organisation --1 ------- n -- CampaignType
Organisation --1 ------- n -- Campaign
Campaign --1 ------- 1 -- Campaign (parent/child dependency)
Campaign --n ------- 1 -- CampaignType

There are much more objects an dependencies but this should be enough to clearify my problem.
All dependencies have the default fetch types: LAZY for to-n dependencies and EAGER for to-1 dependencies.

If I use an HQL query to load a list of campaigns Hibernate generates one SQL statement to load these campaings. After that several SQLs are generated to load the eagerly fetched associations. In the above example it would be: CampaignType, Organisation, OrganisationalUnit (root unit) and User.

As our domain model is much more complex one single HQL leads to 30 SQLs or more sometimes. One of our customers is complaining about this much SQL statements. For that reason we have to optimize the amount of SQL statements executed. Now we are thinking about how to do this.
One possibility is to use explicit fetch joins in the HQL statement so that all to-1 dependencies are fetched in one single SQL, but that leads to very unreadable HQL statements. Another possibility is to make some to-1 dependecies LAZY so that they are not loaded at all. Or we can use @Fetch annotations, but we have to switch to Criteria API then which has some other disadvantages.
Are there any other possibilities? Which is the best fetching strategy for such a domain model?

Regards,
Ole

For the collections, use batch size , and sub select fetching. have lazy=extra.

Hmm, my problem aren't the collections, but the eager loaded to-1 relations like Campaign-to-Organisation.
My collections are all lazy and are only loaded when accessed. But the entities are eager and therefore automatically loaded by Hibernate. So if I do something like

Hibernate will generate a few sql statements which

1. loads the Campaign
2. loads the CampaignType
3. loads the Organisation
4. loads the User
5. loads the root OrganisationalUnit
6. loads the parent Campaign
7. loads the parent campaigns to-one entities

Hope my problems is described understandable now?