I have a query where I have three objects, and I want to load all three objects eagerly. I've choosen to mark all objects lazy in the annotations just as recommended. So here are my objects:

Device ----> NIC ----> DNS Name

Where Device has many NICs and a NIC has many to one DNS Names.

I can do a query to eagerly load the nics, but I don't know how to specify to load the DNS Names that go with the NICs as well.

from Device d left join fetch d.nics left fetch join d.nics.dns

Unfortunately the above query doesn't work because nics is a set and not a NIC instance. How do I specify that I want join the NIC instances with their DNS Name?

As of right now I see the DNS names being loaded one by one resulting in the N+1 query problem.

Thanks
Charlie

Why don't you leave everything LAZY and query at the NIC level instead of pulling from the top-down?

This is pretty common w/ large hierarchies. You could pull NIC and then left join fetch to Device & DNS Name.

I hadn't thought about that. That's pretty creative. I'm not positive that would work since my view wants the devices displayed along with their NICs and DNS. I can see if it works or not.

So is this to say I can't do this type of deep query joins? I am just curious if it's possible. This has got to be a common thing as you said with large hierarchies. It would only make sense that Hibernate/EJB provide assistance in this matter. You can do it with SQL pretty easy at least.

Charlie

I'm pretty sure (though I haven't read to confirm) that the JPA spec doesn't support joins at that level, though Hibernate *can* handle it, it only seems to work if you're not chaining out through a collection.

Again, don't take my word for it...I'm just recalling from memory...I could be wrong.

I know this query works for me but I'm joining 2 levels deeper through single entities:



Anyhow, w/ some fenagling (sp?) you should be able to just approach the model from the middle and get the same data....I do the same trick when I want the app to perform a little better.